[RFC,v3,11/12] firmware: arm_scmi: Add virtio transport

Commit Message

Peter Hilber May 11, 2021, 12:20 a.m. UTC

From: Igor Skalkin <[e-mail]>

This transport enables accessing an SCMI platform as a virtio device.

Implement an SCMI virtio driver according to the virtio SCMI device spec
[1]. Virtio device id 32 has been reserved for the SCMI device [2].

The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
at most one Rx channel (virtio eventq, P2A channel).

The following feature bit defined in [1] is not implemented:
VIRTIO_SCMI_F_SHARED_MEMORY.

After the preparatory patches, this implements the virtio transport as
paraphrased:

Only support a single arm-scmi device (which is consistent with the SCMI
spec). scmi-virtio init is called from arm-scmi module init. During the
arm-scmi probing, link to the first probed scmi-virtio device. Defer
arm-scmi probing if no scmi-virtio device is bound yet.

For simplicity, restrict the number of messages which can be pending
simultaneously according to the virtqueue capacity. (The virtqueue sizes
are negotiated with the virtio device.)

As soon as Rx channel message buffers are allocated or have been read
out by the arm-scmi driver, feed them to the virtio device.

Since some virtio devices may not have the short response time exhibited
by SCMI platforms using other transports, set a generous response
timeout.

Limitations:

- Polling is not supported.

- The timeout for delayed responses has not been adjusted.

[1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
[2] https://www.oasis-open.org/committees/ballot.php?id=3496

Signed-off-by: Igor Skalkin <[e-mail]>
[ Peter: Adapted patch for submission to upstream. ]
Co-developed-by: Peter Hilber <[e-mail]>
Signed-off-by: Peter Hilber <[e-mail]>
---
 MAINTAINERS                        |   1 +
 drivers/firmware/Kconfig           |  12 +
 drivers/firmware/arm_scmi/Makefile |   1 +
 drivers/firmware/arm_scmi/common.h |   3 +
 drivers/firmware/arm_scmi/driver.c |   3 +
 drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
 include/uapi/linux/virtio_ids.h    |   1 +
 include/uapi/linux/virtio_scmi.h   |  25 ++
 8 files changed, 569 insertions(+)
 create mode 100644 drivers/firmware/arm_scmi/virtio.c
 create mode 100644 include/uapi/linux/virtio_scmi.h

Comments

Cristian Marussi May 18, 2021, 8:08 a.m. UTC | #1

Hi Peter,

On Tue, May 11, 2021 at 02:20:39AM +0200, Peter Hilber wrote:
> From: Igor Skalkin <[e-mail]>
> 
> This transport enables accessing an SCMI platform as a virtio device.
> 
> Implement an SCMI virtio driver according to the virtio SCMI device spec
> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
> 
> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> at most one Rx channel (virtio eventq, P2A channel).
> 
> The following feature bit defined in [1] is not implemented:
> VIRTIO_SCMI_F_SHARED_MEMORY.
> 
> After the preparatory patches, this implements the virtio transport as
> paraphrased:
> 
> Only support a single arm-scmi device (which is consistent with the SCMI
> spec). scmi-virtio init is called from arm-scmi module init. During the
> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> arm-scmi probing if no scmi-virtio device is bound yet.
> 
> For simplicity, restrict the number of messages which can be pending
> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> are negotiated with the virtio device.)
> 
> As soon as Rx channel message buffers are allocated or have been read
> out by the arm-scmi driver, feed them to the virtio device.
> 
> Since some virtio devices may not have the short response time exhibited
> by SCMI platforms using other transports, set a generous response
> timeout.
> 
> Limitations:
> 
> - Polling is not supported.
> 
> - The timeout for delayed responses has not been adjusted.
> 

I want to give you some feedback/update while I'm reworking this series.

My main concerns currently arise from the logic of the interaction with
the core transport layer and the race resolution logic that you added in
the final patch, but I understand that, as said, this stems from the
current assumptions built into the core about transports.

So I tried to radically simplify this interactions modifying the core
accordingly and I now have something working (even though still a bit
dirty): so my plan would be in the next days to post an updated RFC V4 with
some core changes upfront, plus your V3 with patches 7,8,12 dropped and a
cumulative patch on virtio transport patch 11 (to better highlight the
differences) and get some feedback at first. (and tessing if you can :D)

I'm fine with the message abstractions introduced in patch 09.

I still have not addressed the probing sequence issues (as discussed),
nor included some work I'm doing on atomicity and polling of the transport
(and I've just seen Rob email about DT), so such RFC V4 will be anyway
somehow transitional, in order to share and get your feedback and see if
I missed something along the way.

Anyway, in a nutshell, I think that the main issues mentioned above derive
from the fact that the virtio transport is forced to cope with the assumption,
currently present in the core model, that a transport needs to handle msg
payloads and hdrs in two different steps, while virtio clearly is ready
to go as soon as the resp/notif/dresp msg are received from the vqueues
and this leads to the need of passing back and forth transport specific
ancillary data (like msg_handle) and complicates the handling and syncing
of the states of the inflight messages between the core and the virtio
transport.

So...I'm making fetch_response/notification optional to the core :D, such
that if a transport like virtio does not offer such ops, the new assumption
in the core is that, when scmi_rx_callback(cinfo, msg_hdr) is called,
a transport like virtio would have already completely filled up the xfer
and there's no need to call fetch_* since all is ready to go; in order to
do that, I added a couple of helpers in the core for the transport to be
able to grab, based only in msg_hdr, the proper pending xfer (for resp/
dresp since they are tied uniquely to the seq/token in the hdr matching the
original sent cmd) or have a freshly allocated xfer assigned (for notif):
this way the transport RX callback (like vio_complete) can now effectively
fillup completely the xfer and release the vqueue message before even
calling scmi_rx_callback. (and also I added a bit of additional sync logic
in and around xfer to avoid races against stale and possibly reused xfers.)

This seemed to me a bit less complicated and with fewer core/transport sync
issue sthan the actual solution so I gave it a try.

As of now it works for me in my minimal emulated setup for cmd/resp/dresp/
notif using sensors proto via scmi_iio/hwmon as a testbed (like it was
working indeed with your V3 original series, so this is conforting :D),
but I want to make more test on a real virtio backend and cleanup a bit
the series before posting an intermediate V4 RFC as said.

Thanks,
Cristian

> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
> 
> Signed-off-by: Igor Skalkin <[e-mail]>
> [ Peter: Adapted patch for submission to upstream. ]
> Co-developed-by: Peter Hilber <[e-mail]>
> Signed-off-by: Peter Hilber <[e-mail]>
> ---
>  MAINTAINERS                        |   1 +
>  drivers/firmware/Kconfig           |  12 +
>  drivers/firmware/arm_scmi/Makefile |   1 +
>  drivers/firmware/arm_scmi/common.h |   3 +
>  drivers/firmware/arm_scmi/driver.c |   3 +
>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_scmi.h   |  25 ++
>  8 files changed, 569 insertions(+)
>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>  create mode 100644 include/uapi/linux/virtio_scmi.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index bd7aff0c120f..449c336872f3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17705,6 +17705,7 @@ F:	drivers/regulator/scmi-regulator.c
>  F:	drivers/reset/reset-scmi.c
>  F:	include/linux/sc[mp]i_protocol.h
>  F:	include/trace/events/scmi.h
> +F:	include/uapi/linux/virtio_scmi.h
>  
>  SYSTEM RESET/SHUTDOWN DRIVERS
>  M:	Sebastian Reichel <[e-mail]>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index e8377b12e4d0..7e9eafdd9b63 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>  	  This declares whether a message passing based transport for SCMI is
>  	  available.
>  
> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
> +# this config doesn't show up when SCMI wouldn't be available.
> +config VIRTIO_SCMI
> +	bool "Virtio transport for SCMI"
> +	select ARM_SCMI_HAVE_MSG
> +	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
> +	help
> +	  This enables the virtio based transport for SCMI.
> +
> +	  If you want to use the ARM SCMI protocol between the virtio guest and
> +	  a host providing a virtio SCMI device, answer Y.
> +
>  config ARM_SCMI_POWER_DOMAIN
>  	tristate "SCMI power domain driver"
>  	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> index f6b4acb8abdb..db1787606fb2 100644
> --- a/drivers/firmware/arm_scmi/Makefile
> +++ b/drivers/firmware/arm_scmi/Makefile
> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>  		    $(scmi-transport-y)
> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> index 4cb6571c7aaf..bada06cfd33d 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>  #ifdef CONFIG_HAVE_ARM_SMCCC
>  extern const struct scmi_desc scmi_smc_desc;
>  #endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +extern const struct scmi_desc scmi_virtio_desc;
> +#endif
>  
>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>  void *scmi_get_transport_info(struct device *dev);
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index e04e7c8e6928..a31187385470 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>  #endif
>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>  	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> +#endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>  #endif
>  	{ /* Sentinel */ },
>  };
> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> new file mode 100644
> index 000000000000..20972adf6dc7
> --- /dev/null
> +++ b/drivers/firmware/arm_scmi/virtio.c
> @@ -0,0 +1,523 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Virtio Transport driver for Arm System Control and Management Interface
> + * (SCMI).
> + *
> + * Copyright (C) 2020 OpenSynergy.
> + */
> +
> +/**
> + * DOC: Theory of Operation
> + *
> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
> + *
> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
> + * virtqueue. Access to each virtqueue is protected by spinlocks.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_scmi.h>
> +
> +#include "common.h"
> +
> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
> +	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
> +#define DESCRIPTORS_PER_TX_MSG 2
> +
> +/**
> + * struct scmi_vio_channel - Transport channel information
> + *
> + * @lock: Protects access to all members except ready.
> + * @ready_lock: Protects access to ready. If required, it must be taken before
> + *              lock.
> + * @vqueue: Associated virtqueue
> + * @cinfo: SCMI Tx or Rx channel
> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> + * @is_rx: Whether channel is an Rx channel
> + * @ready: Whether transport user is ready to hear about channel
> + */
> +struct scmi_vio_channel {
> +	spinlock_t lock;
> +	spinlock_t ready_lock;
> +	struct virtqueue *vqueue;
> +	struct scmi_chan_info *cinfo;
> +	struct list_head free_list;
> +	u8 is_rx;
> +	u8 ready;
> +};
> +
> +/**
> + * struct scmi_vio_msg - Transport PDU information
> + *
> + * @request: SDU used for commands
> + * @input: SDU used for (delayed) responses and notifications
> + * @list: List which scmi_vio_msg may be part of
> + * @rx_len: Input SDU size in bytes, once input has been received
> + */
> +struct scmi_vio_msg {
> +	struct scmi_msg_payld *request;
> +	struct scmi_msg_payld *input;
> +	struct list_head list;
> +	unsigned int rx_len;
> +};
> +
> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> +{
> +	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> +}
> +
> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> +			       struct scmi_vio_msg *msg)
> +{
> +	struct scatterlist sg_in;
> +	int rc;
> +	unsigned long flags;
> +
> +	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +
> +	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
> +	if (rc)
> +		dev_err_once(vioch->cinfo->dev,
> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> +			     rc);
> +	else
> +		virtqueue_kick(vioch->vqueue);
> +
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	return rc;
> +}
> +
> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> +{
> +	unsigned long ready_flags;
> +	unsigned long flags;
> +	unsigned int length;
> +	struct scmi_vio_channel *vioch;
> +	struct scmi_vio_msg *msg;
> +	bool cb_enabled = true;
> +
> +	if (WARN_ON_ONCE(!vqueue->vdev->priv))
> +		return;
> +	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
> +
> +	for (;;) {
> +		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
> +
> +		if (!vioch->ready) {
> +			if (!cb_enabled)
> +				(void)virtqueue_enable_cb(vqueue);
> +			goto unlock_ready_out;
> +		}
> +
> +		spin_lock_irqsave(&vioch->lock, flags);
> +		if (cb_enabled) {
> +			virtqueue_disable_cb(vqueue);
> +			cb_enabled = false;
> +		}
> +		msg = virtqueue_get_buf(vqueue, &length);
> +		if (!msg) {
> +			if (virtqueue_enable_cb(vqueue))
> +				goto unlock_out;
> +			else
> +				cb_enabled = true;
> +		}
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +		if (msg) {
> +			msg->rx_len = length;
> +
> +			/*
> +			 * Hold the ready_lock during the callback to avoid
> +			 * races when the arm-scmi driver is unbinding while
> +			 * the virtio device is not quiesced yet.
> +			 */
> +			scmi_rx_callback(vioch->cinfo,
> +					 msg_read_header(msg->input), msg);
> +		}
> +		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +	}
> +
> +unlock_out:
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +unlock_ready_out:
> +	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +}
> +
> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
> +
> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
> +	scmi_vio_complete_cb,
> +	scmi_vio_complete_cb
> +};
> +
> +static unsigned int virtio_get_max_msg(bool tx,
> +				       struct scmi_chan_info *base_cinfo)
> +{
> +	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> +	unsigned int ret;
> +
> +	ret = virtqueue_get_vring_size(vioch->vqueue);
> +
> +	/* Tx messages need multiple descriptors. */
> +	if (tx)
> +		ret /= DESCRIPTORS_PER_TX_MSG;
> +
> +	if (ret > MSG_TOKEN_MAX) {
> +		dev_info_once(
> +			base_cinfo->dev,
> +			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> +			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> +		ret = MSG_TOKEN_MAX;
> +	}
> +
> +	return ret;
> +}
> +
> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> +{
> +	return 1;
> +}
> +
> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> +
> +static int virtio_link_supplier(struct device *dev)
> +{
> +	struct device *vdev = driver_find_device(
> +		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> +
> +	if (!vdev) {
> +		dev_notice_once(
> +			dev,
> +			"Deferring probe after not finding a bound scmi-virtio device\n");
> +		return -EPROBE_DEFER;
> +	}
> +
> +	/* Add device link for remove order and sysfs link. */
> +	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> +		put_device(vdev);
> +		dev_err(dev, "Adding link to supplier virtio device failed\n");
> +		return -ECANCELED;
> +	}
> +
> +	put_device(vdev);
> +	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> +}
> +
> +static bool virtio_chan_available(struct device *dev, int idx)
> +{
> +	struct virtio_device *vdev;
> +
> +	/* scmi-virtio doesn't support per-protocol channels */
> +	if (is_scmi_protocol_device(dev))
> +		return false;
> +
> +	vdev = scmi_get_transport_info(dev);
> +	if (!vdev)
> +		return false;
> +
> +	switch (idx) {
> +	case VIRTIO_SCMI_VQ_TX:
> +		return true;
> +	case VIRTIO_SCMI_VQ_RX:
> +		return scmi_vio_have_vq_rx(vdev);
> +	default:
> +		return false;
> +	}
> +}
> +
> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> +			     bool tx)
> +{
> +	unsigned long flags;
> +	struct virtio_device *vdev;
> +	struct scmi_vio_channel *vioch;
> +	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> +	int max_msg;
> +	int i;
> +
> +	if (!virtio_chan_available(dev, index))
> +		return -ENODEV;
> +
> +	vdev = scmi_get_transport_info(dev);
> +	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +	cinfo->transport_info = vioch;
> +	vioch->cinfo = cinfo;
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	max_msg = virtio_get_max_msg(tx, cinfo);
> +
> +	for (i = 0; i < max_msg; i++) {
> +		struct scmi_vio_msg *msg;
> +
> +		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> +		if (!msg)
> +			return -ENOMEM;
> +
> +		if (tx) {
> +			msg->request = devm_kzalloc(cinfo->dev,
> +						    VIRTIO_SCMI_MAX_PDU_SIZE,
> +						    GFP_KERNEL);
> +			if (!msg->request)
> +				return -ENOMEM;
> +		}
> +
> +		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> +					  GFP_KERNEL);
> +		if (!msg->input)
> +			return -ENOMEM;
> +
> +		if (tx) {
> +			spin_lock_irqsave(&vioch->lock, flags);
> +			list_add_tail(&msg->list, &vioch->free_list);
> +			spin_unlock_irqrestore(&vioch->lock, flags);
> +		} else {
> +			scmi_vio_feed_vq_rx(vioch, msg);
> +		}
> +	}
> +
> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> +	vioch->ready = true;
> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +	return 0;
> +}
> +
> +static int virtio_chan_free(int id, void *p, void *data)
> +{
> +	unsigned long flags;
> +	struct scmi_chan_info *cinfo = p;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> +	vioch->ready = false;
> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +	scmi_free_channel(cinfo, data, id);
> +	return 0;
> +}
> +
> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> +			       struct scmi_xfer *xfer)
> +{
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +	struct scatterlist sg_out;
> +	struct scatterlist sg_in;
> +	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> +	unsigned long flags;
> +	int rc;
> +	struct scmi_vio_msg *msg;
> +
> +	/*
> +	 * TODO: For now, we don't support polling. But it should not be
> +	 * difficult to add support.
> +	 */
> +	if (xfer->hdr.poll_completion)
> +		return -EINVAL;
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +
> +	if (list_empty(&vioch->free_list)) {
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +		return -EBUSY;
> +	}
> +
> +	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> +	list_del(&msg->list);
> +
> +	msg_tx_prepare(msg->request, xfer);
> +
> +	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> +	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> +
> +	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> +	if (rc) {
> +		list_add(&msg->list, &vioch->free_list);
> +		dev_err_once(vioch->cinfo->dev,
> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> +			     rc);
> +	} else {
> +		virtqueue_kick(vioch->vqueue);
> +	}
> +
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	return rc;
> +}
> +
> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> +				  struct scmi_xfer *xfer, void *msg_handle)
> +{
> +	struct scmi_vio_msg *msg = msg_handle;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	msg_fetch_response(msg->input, msg->rx_len, xfer);
> +}
> +
> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> +				      size_t max_len, struct scmi_xfer *xfer,
> +				      void *msg_handle)
> +{
> +	struct scmi_vio_msg *msg = msg_handle;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> +}
> +
> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> +{
> +}
> +
> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> +			    struct scmi_xfer *xfer)
> +{
> +	return false;
> +}
> +
> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> +{
> +	unsigned long flags;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +	struct scmi_vio_msg *msg = msg_handle;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	if (vioch->is_rx) {
> +		scmi_vio_feed_vq_rx(vioch, msg);
> +	} else {
> +		spin_lock_irqsave(&vioch->lock, flags);
> +		list_add(&msg->list, &vioch->free_list);
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +	}
> +}
> +
> +static const struct scmi_transport_ops scmi_virtio_ops = {
> +	.link_supplier = virtio_link_supplier,
> +	.chan_available = virtio_chan_available,
> +	.chan_setup = virtio_chan_setup,
> +	.chan_free = virtio_chan_free,
> +	.get_max_msg = virtio_get_max_msg,
> +	.send_message = virtio_send_message,
> +	.fetch_response = virtio_fetch_response,
> +	.fetch_notification = virtio_fetch_notification,
> +	.clear_channel = dummy_clear_channel,
> +	.poll_done = dummy_poll_done,
> +	.drop_message = virtio_drop_message,
> +};
> +
> +static int scmi_vio_probe(struct virtio_device *vdev)
> +{
> +	struct device *dev = &vdev->dev;
> +	struct scmi_vio_channel *channels;
> +	bool have_vq_rx;
> +	int vq_cnt;
> +	int i;
> +	int ret;
> +	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> +
> +	have_vq_rx = scmi_vio_have_vq_rx(vdev);
> +	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> +
> +	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> +	if (!channels)
> +		return -ENOMEM;
> +
> +	if (have_vq_rx)
> +		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> +
> +	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> +			      scmi_vio_vqueue_names, NULL);
> +	if (ret) {
> +		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> +		return ret;
> +	}
> +	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> +
> +	for (i = 0; i < vq_cnt; i++) {
> +		spin_lock_init(&channels[i].lock);
> +		spin_lock_init(&channels[i].ready_lock);
> +		INIT_LIST_HEAD(&channels[i].free_list);
> +		channels[i].vqueue = vqs[i];
> +	}
> +
> +	vdev->priv = channels;
> +
> +	return 0;
> +}
> +
> +static void scmi_vio_remove(struct virtio_device *vdev)
> +{
> +	vdev->config->reset(vdev);
> +	vdev->config->del_vqs(vdev);
> +}
> +
> +static unsigned int features[] = {
> +	VIRTIO_SCMI_F_P2A_CHANNELS,
> +};
> +
> +static const struct virtio_device_id id_table[] = {
> +	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> +	{ 0 }
> +};
> +
> +static struct virtio_driver virtio_scmi_driver = {
> +	.driver.name = "scmi-virtio",
> +	.driver.owner = THIS_MODULE,
> +	.feature_table = features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.id_table = id_table,
> +	.probe = scmi_vio_probe,
> +	.remove = scmi_vio_remove,
> +};
> +
> +static int __init virtio_scmi_init(void)
> +{
> +	return register_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +static void __exit virtio_scmi_exit(void)
> +{
> +	unregister_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +const struct scmi_desc scmi_virtio_desc = {
> +	.init = virtio_scmi_init,
> +	.exit = virtio_scmi_exit,
> +	.ops = &scmi_virtio_ops,
> +	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> +	.max_msg = 0, /* overridden by virtio_get_max_msg() */
> +	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> +};
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index f0c35ce8628c..c146fe30e589 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -56,5 +56,6 @@
>  #define VIRTIO_ID_PMEM			27 /* virtio pmem */
>  #define VIRTIO_ID_BT			28 /* virtio bluetooth */
>  #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
> +#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
>  
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> new file mode 100644
> index 000000000000..732b01504c35
> --- /dev/null
> +++ b/include/uapi/linux/virtio_scmi.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> +/*
> + * Copyright (C) 2020 OpenSynergy GmbH
> + */
> +
> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> +
> +#include <linux/virtio_types.h>
> +
> +/* Feature bits */
> +
> +/* Device implements some SCMI notifications, or delayed responses. */
> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> +
> +/* Device implements any SCMI statistics shared memory region */
> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> +
> +/* Virtqueues */
> +
> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> +
> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> -- 
> 2.25.1
> 
>

Cristian Marussi May 26, 2021, 2:40 p.m. UTC | #2

Hi Peter,

as anticipated I'm adding some new SCMI core mechanisms that should help
simplyfying virtio-scmi series.

Such core work is still in progress (and to be properly reviewed) and it
is at:

https://lore.kernel.org/linux-arm-kernel/[e-mail]/

but in the meantime I have an initial but working (for me at least :D)
rework of your V3 virtio-scmi series; rework is still in progress and to be
cleaned up (nor I have addressed probing sequence or polling mode), and I am
anyway holding it for now since Rob asked about DT txt-to-yaml conversion
too, BUT if you can or want to have a look in the meantime, you can find the
whole V4 transitional series rebased on top of my core changes with some
changes on top at:

https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_virtio_trans_V4_rework/

where:

 - I dropped V3 patches 7,8,12
 - the virtio changes I applied to make use of my core changes are all
   embedded in the last patch (just for now):
   
 	[RFC] firmware: arm_scmi: make virtio-scmi use delegated xfers

Definitely not the final version, so you may want to just wait for a
real V4, but just to give an idea of the direction I'm trying to follow
if you want.

Thanks,
Cristian

On Tue, May 11, 2021 at 02:20:39AM +0200, Peter Hilber wrote:
> From: Igor Skalkin <[e-mail]>
> 
> This transport enables accessing an SCMI platform as a virtio device.
> 
> Implement an SCMI virtio driver according to the virtio SCMI device spec
> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
> 
> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> at most one Rx channel (virtio eventq, P2A channel).
> 
> The following feature bit defined in [1] is not implemented:
> VIRTIO_SCMI_F_SHARED_MEMORY.
> 
> After the preparatory patches, this implements the virtio transport as
> paraphrased:
> 
> Only support a single arm-scmi device (which is consistent with the SCMI
> spec). scmi-virtio init is called from arm-scmi module init. During the
> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> arm-scmi probing if no scmi-virtio device is bound yet.
> 
> For simplicity, restrict the number of messages which can be pending
> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> are negotiated with the virtio device.)
> 
> As soon as Rx channel message buffers are allocated or have been read
> out by the arm-scmi driver, feed them to the virtio device.
> 
> Since some virtio devices may not have the short response time exhibited
> by SCMI platforms using other transports, set a generous response
> timeout.
> 
> Limitations:
> 
> - Polling is not supported.
> 
> - The timeout for delayed responses has not been adjusted.
> 
> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
> 
> Signed-off-by: Igor Skalkin <[e-mail]>
> [ Peter: Adapted patch for submission to upstream. ]
> Co-developed-by: Peter Hilber <[e-mail]>
> Signed-off-by: Peter Hilber <[e-mail]>
> ---
>  MAINTAINERS                        |   1 +
>  drivers/firmware/Kconfig           |  12 +
>  drivers/firmware/arm_scmi/Makefile |   1 +
>  drivers/firmware/arm_scmi/common.h |   3 +
>  drivers/firmware/arm_scmi/driver.c |   3 +
>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_scmi.h   |  25 ++
>  8 files changed, 569 insertions(+)
>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>  create mode 100644 include/uapi/linux/virtio_scmi.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index bd7aff0c120f..449c336872f3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17705,6 +17705,7 @@ F:	drivers/regulator/scmi-regulator.c
>  F:	drivers/reset/reset-scmi.c
>  F:	include/linux/sc[mp]i_protocol.h
>  F:	include/trace/events/scmi.h
> +F:	include/uapi/linux/virtio_scmi.h
>  
>  SYSTEM RESET/SHUTDOWN DRIVERS
>  M:	Sebastian Reichel <[e-mail]>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index e8377b12e4d0..7e9eafdd9b63 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>  	  This declares whether a message passing based transport for SCMI is
>  	  available.
>  
> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
> +# this config doesn't show up when SCMI wouldn't be available.
> +config VIRTIO_SCMI
> +	bool "Virtio transport for SCMI"
> +	select ARM_SCMI_HAVE_MSG
> +	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
> +	help
> +	  This enables the virtio based transport for SCMI.
> +
> +	  If you want to use the ARM SCMI protocol between the virtio guest and
> +	  a host providing a virtio SCMI device, answer Y.
> +
>  config ARM_SCMI_POWER_DOMAIN
>  	tristate "SCMI power domain driver"
>  	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> index f6b4acb8abdb..db1787606fb2 100644
> --- a/drivers/firmware/arm_scmi/Makefile
> +++ b/drivers/firmware/arm_scmi/Makefile
> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>  		    $(scmi-transport-y)
> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> index 4cb6571c7aaf..bada06cfd33d 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>  #ifdef CONFIG_HAVE_ARM_SMCCC
>  extern const struct scmi_desc scmi_smc_desc;
>  #endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +extern const struct scmi_desc scmi_virtio_desc;
> +#endif
>  
>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>  void *scmi_get_transport_info(struct device *dev);
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index e04e7c8e6928..a31187385470 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>  #endif
>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>  	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> +#endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>  #endif
>  	{ /* Sentinel */ },
>  };
> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> new file mode 100644
> index 000000000000..20972adf6dc7
> --- /dev/null
> +++ b/drivers/firmware/arm_scmi/virtio.c
> @@ -0,0 +1,523 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Virtio Transport driver for Arm System Control and Management Interface
> + * (SCMI).
> + *
> + * Copyright (C) 2020 OpenSynergy.
> + */
> +
> +/**
> + * DOC: Theory of Operation
> + *
> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
> + *
> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
> + * virtqueue. Access to each virtqueue is protected by spinlocks.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_scmi.h>
> +
> +#include "common.h"
> +
> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
> +	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
> +#define DESCRIPTORS_PER_TX_MSG 2
> +
> +/**
> + * struct scmi_vio_channel - Transport channel information
> + *
> + * @lock: Protects access to all members except ready.
> + * @ready_lock: Protects access to ready. If required, it must be taken before
> + *              lock.
> + * @vqueue: Associated virtqueue
> + * @cinfo: SCMI Tx or Rx channel
> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> + * @is_rx: Whether channel is an Rx channel
> + * @ready: Whether transport user is ready to hear about channel
> + */
> +struct scmi_vio_channel {
> +	spinlock_t lock;
> +	spinlock_t ready_lock;
> +	struct virtqueue *vqueue;
> +	struct scmi_chan_info *cinfo;
> +	struct list_head free_list;
> +	u8 is_rx;
> +	u8 ready;
> +};
> +
> +/**
> + * struct scmi_vio_msg - Transport PDU information
> + *
> + * @request: SDU used for commands
> + * @input: SDU used for (delayed) responses and notifications
> + * @list: List which scmi_vio_msg may be part of
> + * @rx_len: Input SDU size in bytes, once input has been received
> + */
> +struct scmi_vio_msg {
> +	struct scmi_msg_payld *request;
> +	struct scmi_msg_payld *input;
> +	struct list_head list;
> +	unsigned int rx_len;
> +};
> +
> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> +{
> +	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> +}
> +
> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> +			       struct scmi_vio_msg *msg)
> +{
> +	struct scatterlist sg_in;
> +	int rc;
> +	unsigned long flags;
> +
> +	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +
> +	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
> +	if (rc)
> +		dev_err_once(vioch->cinfo->dev,
> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> +			     rc);
> +	else
> +		virtqueue_kick(vioch->vqueue);
> +
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	return rc;
> +}
> +
> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> +{
> +	unsigned long ready_flags;
> +	unsigned long flags;
> +	unsigned int length;
> +	struct scmi_vio_channel *vioch;
> +	struct scmi_vio_msg *msg;
> +	bool cb_enabled = true;
> +
> +	if (WARN_ON_ONCE(!vqueue->vdev->priv))
> +		return;
> +	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
> +
> +	for (;;) {
> +		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
> +
> +		if (!vioch->ready) {
> +			if (!cb_enabled)
> +				(void)virtqueue_enable_cb(vqueue);
> +			goto unlock_ready_out;
> +		}
> +
> +		spin_lock_irqsave(&vioch->lock, flags);
> +		if (cb_enabled) {
> +			virtqueue_disable_cb(vqueue);
> +			cb_enabled = false;
> +		}
> +		msg = virtqueue_get_buf(vqueue, &length);
> +		if (!msg) {
> +			if (virtqueue_enable_cb(vqueue))
> +				goto unlock_out;
> +			else
> +				cb_enabled = true;
> +		}
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +		if (msg) {
> +			msg->rx_len = length;
> +
> +			/*
> +			 * Hold the ready_lock during the callback to avoid
> +			 * races when the arm-scmi driver is unbinding while
> +			 * the virtio device is not quiesced yet.
> +			 */
> +			scmi_rx_callback(vioch->cinfo,
> +					 msg_read_header(msg->input), msg);
> +		}
> +		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +	}
> +
> +unlock_out:
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +unlock_ready_out:
> +	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +}
> +
> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
> +
> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
> +	scmi_vio_complete_cb,
> +	scmi_vio_complete_cb
> +};
> +
> +static unsigned int virtio_get_max_msg(bool tx,
> +				       struct scmi_chan_info *base_cinfo)
> +{
> +	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> +	unsigned int ret;
> +
> +	ret = virtqueue_get_vring_size(vioch->vqueue);
> +
> +	/* Tx messages need multiple descriptors. */
> +	if (tx)
> +		ret /= DESCRIPTORS_PER_TX_MSG;
> +
> +	if (ret > MSG_TOKEN_MAX) {
> +		dev_info_once(
> +			base_cinfo->dev,
> +			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> +			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> +		ret = MSG_TOKEN_MAX;
> +	}
> +
> +	return ret;
> +}
> +
> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> +{
> +	return 1;
> +}
> +
> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> +
> +static int virtio_link_supplier(struct device *dev)
> +{
> +	struct device *vdev = driver_find_device(
> +		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> +
> +	if (!vdev) {
> +		dev_notice_once(
> +			dev,
> +			"Deferring probe after not finding a bound scmi-virtio device\n");
> +		return -EPROBE_DEFER;
> +	}
> +
> +	/* Add device link for remove order and sysfs link. */
> +	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> +		put_device(vdev);
> +		dev_err(dev, "Adding link to supplier virtio device failed\n");
> +		return -ECANCELED;
> +	}
> +
> +	put_device(vdev);
> +	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> +}
> +
> +static bool virtio_chan_available(struct device *dev, int idx)
> +{
> +	struct virtio_device *vdev;
> +
> +	/* scmi-virtio doesn't support per-protocol channels */
> +	if (is_scmi_protocol_device(dev))
> +		return false;
> +
> +	vdev = scmi_get_transport_info(dev);
> +	if (!vdev)
> +		return false;
> +
> +	switch (idx) {
> +	case VIRTIO_SCMI_VQ_TX:
> +		return true;
> +	case VIRTIO_SCMI_VQ_RX:
> +		return scmi_vio_have_vq_rx(vdev);
> +	default:
> +		return false;
> +	}
> +}
> +
> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> +			     bool tx)
> +{
> +	unsigned long flags;
> +	struct virtio_device *vdev;
> +	struct scmi_vio_channel *vioch;
> +	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> +	int max_msg;
> +	int i;
> +
> +	if (!virtio_chan_available(dev, index))
> +		return -ENODEV;
> +
> +	vdev = scmi_get_transport_info(dev);
> +	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +	cinfo->transport_info = vioch;
> +	vioch->cinfo = cinfo;
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	max_msg = virtio_get_max_msg(tx, cinfo);
> +
> +	for (i = 0; i < max_msg; i++) {
> +		struct scmi_vio_msg *msg;
> +
> +		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> +		if (!msg)
> +			return -ENOMEM;
> +
> +		if (tx) {
> +			msg->request = devm_kzalloc(cinfo->dev,
> +						    VIRTIO_SCMI_MAX_PDU_SIZE,
> +						    GFP_KERNEL);
> +			if (!msg->request)
> +				return -ENOMEM;
> +		}
> +
> +		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> +					  GFP_KERNEL);
> +		if (!msg->input)
> +			return -ENOMEM;
> +
> +		if (tx) {
> +			spin_lock_irqsave(&vioch->lock, flags);
> +			list_add_tail(&msg->list, &vioch->free_list);
> +			spin_unlock_irqrestore(&vioch->lock, flags);
> +		} else {
> +			scmi_vio_feed_vq_rx(vioch, msg);
> +		}
> +	}
> +
> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> +	vioch->ready = true;
> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +	return 0;
> +}
> +
> +static int virtio_chan_free(int id, void *p, void *data)
> +{
> +	unsigned long flags;
> +	struct scmi_chan_info *cinfo = p;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> +	vioch->ready = false;
> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +	scmi_free_channel(cinfo, data, id);
> +	return 0;
> +}
> +
> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> +			       struct scmi_xfer *xfer)
> +{
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +	struct scatterlist sg_out;
> +	struct scatterlist sg_in;
> +	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> +	unsigned long flags;
> +	int rc;
> +	struct scmi_vio_msg *msg;
> +
> +	/*
> +	 * TODO: For now, we don't support polling. But it should not be
> +	 * difficult to add support.
> +	 */
> +	if (xfer->hdr.poll_completion)
> +		return -EINVAL;
> +
> +	spin_lock_irqsave(&vioch->lock, flags);
> +
> +	if (list_empty(&vioch->free_list)) {
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +		return -EBUSY;
> +	}
> +
> +	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> +	list_del(&msg->list);
> +
> +	msg_tx_prepare(msg->request, xfer);
> +
> +	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> +	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> +
> +	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> +	if (rc) {
> +		list_add(&msg->list, &vioch->free_list);
> +		dev_err_once(vioch->cinfo->dev,
> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> +			     rc);
> +	} else {
> +		virtqueue_kick(vioch->vqueue);
> +	}
> +
> +	spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +	return rc;
> +}
> +
> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> +				  struct scmi_xfer *xfer, void *msg_handle)
> +{
> +	struct scmi_vio_msg *msg = msg_handle;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	msg_fetch_response(msg->input, msg->rx_len, xfer);
> +}
> +
> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> +				      size_t max_len, struct scmi_xfer *xfer,
> +				      void *msg_handle)
> +{
> +	struct scmi_vio_msg *msg = msg_handle;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> +}
> +
> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> +{
> +}
> +
> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> +			    struct scmi_xfer *xfer)
> +{
> +	return false;
> +}
> +
> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> +{
> +	unsigned long flags;
> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> +	struct scmi_vio_msg *msg = msg_handle;
> +
> +	if (!msg) {
> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> +			     "Ignoring %s() call with NULL msg_handle\n",
> +			     __func__);
> +		return;
> +	}
> +
> +	if (vioch->is_rx) {
> +		scmi_vio_feed_vq_rx(vioch, msg);
> +	} else {
> +		spin_lock_irqsave(&vioch->lock, flags);
> +		list_add(&msg->list, &vioch->free_list);
> +		spin_unlock_irqrestore(&vioch->lock, flags);
> +	}
> +}
> +
> +static const struct scmi_transport_ops scmi_virtio_ops = {
> +	.link_supplier = virtio_link_supplier,
> +	.chan_available = virtio_chan_available,
> +	.chan_setup = virtio_chan_setup,
> +	.chan_free = virtio_chan_free,
> +	.get_max_msg = virtio_get_max_msg,
> +	.send_message = virtio_send_message,
> +	.fetch_response = virtio_fetch_response,
> +	.fetch_notification = virtio_fetch_notification,
> +	.clear_channel = dummy_clear_channel,
> +	.poll_done = dummy_poll_done,
> +	.drop_message = virtio_drop_message,
> +};
> +
> +static int scmi_vio_probe(struct virtio_device *vdev)
> +{
> +	struct device *dev = &vdev->dev;
> +	struct scmi_vio_channel *channels;
> +	bool have_vq_rx;
> +	int vq_cnt;
> +	int i;
> +	int ret;
> +	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> +
> +	have_vq_rx = scmi_vio_have_vq_rx(vdev);
> +	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> +
> +	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> +	if (!channels)
> +		return -ENOMEM;
> +
> +	if (have_vq_rx)
> +		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> +
> +	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> +			      scmi_vio_vqueue_names, NULL);
> +	if (ret) {
> +		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> +		return ret;
> +	}
> +	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> +
> +	for (i = 0; i < vq_cnt; i++) {
> +		spin_lock_init(&channels[i].lock);
> +		spin_lock_init(&channels[i].ready_lock);
> +		INIT_LIST_HEAD(&channels[i].free_list);
> +		channels[i].vqueue = vqs[i];
> +	}
> +
> +	vdev->priv = channels;
> +
> +	return 0;
> +}
> +
> +static void scmi_vio_remove(struct virtio_device *vdev)
> +{
> +	vdev->config->reset(vdev);
> +	vdev->config->del_vqs(vdev);
> +}
> +
> +static unsigned int features[] = {
> +	VIRTIO_SCMI_F_P2A_CHANNELS,
> +};
> +
> +static const struct virtio_device_id id_table[] = {
> +	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> +	{ 0 }
> +};
> +
> +static struct virtio_driver virtio_scmi_driver = {
> +	.driver.name = "scmi-virtio",
> +	.driver.owner = THIS_MODULE,
> +	.feature_table = features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.id_table = id_table,
> +	.probe = scmi_vio_probe,
> +	.remove = scmi_vio_remove,
> +};
> +
> +static int __init virtio_scmi_init(void)
> +{
> +	return register_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +static void __exit virtio_scmi_exit(void)
> +{
> +	unregister_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +const struct scmi_desc scmi_virtio_desc = {
> +	.init = virtio_scmi_init,
> +	.exit = virtio_scmi_exit,
> +	.ops = &scmi_virtio_ops,
> +	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> +	.max_msg = 0, /* overridden by virtio_get_max_msg() */
> +	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> +};
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index f0c35ce8628c..c146fe30e589 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -56,5 +56,6 @@
>  #define VIRTIO_ID_PMEM			27 /* virtio pmem */
>  #define VIRTIO_ID_BT			28 /* virtio bluetooth */
>  #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
> +#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
>  
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> new file mode 100644
> index 000000000000..732b01504c35
> --- /dev/null
> +++ b/include/uapi/linux/virtio_scmi.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> +/*
> + * Copyright (C) 2020 OpenSynergy GmbH
> + */
> +
> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> +
> +#include <linux/virtio_types.h>
> +
> +/* Feature bits */
> +
> +/* Device implements some SCMI notifications, or delayed responses. */
> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> +
> +/* Device implements any SCMI statistics shared memory region */
> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> +
> +/* Virtqueues */
> +
> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> +
> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> -- 
> 2.25.1
> 
>

Vincent Guittot June 1, 2021, 2:53 p.m. UTC | #3

On Tue, 11 May 2021 at 02:28, Peter Hilber <[e-mail]> wrote:
>
> From: Igor Skalkin <[e-mail]>
>
> This transport enables accessing an SCMI platform as a virtio device.
>
> Implement an SCMI virtio driver according to the virtio SCMI device spec
> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
>
> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> at most one Rx channel (virtio eventq, P2A channel).
>
> The following feature bit defined in [1] is not implemented:
> VIRTIO_SCMI_F_SHARED_MEMORY.
>
> After the preparatory patches, this implements the virtio transport as
> paraphrased:
>
> Only support a single arm-scmi device (which is consistent with the SCMI
> spec). scmi-virtio init is called from arm-scmi module init. During the
> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> arm-scmi probing if no scmi-virtio device is bound yet.
>
> For simplicity, restrict the number of messages which can be pending
> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> are negotiated with the virtio device.)
>
> As soon as Rx channel message buffers are allocated or have been read
> out by the arm-scmi driver, feed them to the virtio device.
>
> Since some virtio devices may not have the short response time exhibited
> by SCMI platforms using other transports, set a generous response
> timeout.
>
> Limitations:
>
> - Polling is not supported.
>
> - The timeout for delayed responses has not been adjusted.
>
> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
>
> Signed-off-by: Igor Skalkin <[e-mail]>
> [ Peter: Adapted patch for submission to upstream. ]
> Co-developed-by: Peter Hilber <[e-mail]>
> Signed-off-by: Peter Hilber <[e-mail]>
> ---
>  MAINTAINERS                        |   1 +
>  drivers/firmware/Kconfig           |  12 +
>  drivers/firmware/arm_scmi/Makefile |   1 +
>  drivers/firmware/arm_scmi/common.h |   3 +
>  drivers/firmware/arm_scmi/driver.c |   3 +
>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>  include/uapi/linux/virtio_ids.h    |   1 +
>  include/uapi/linux/virtio_scmi.h   |  25 ++
>  8 files changed, 569 insertions(+)
>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>  create mode 100644 include/uapi/linux/virtio_scmi.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index bd7aff0c120f..449c336872f3 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -17705,6 +17705,7 @@ F:      drivers/regulator/scmi-regulator.c
>  F:     drivers/reset/reset-scmi.c
>  F:     include/linux/sc[mp]i_protocol.h
>  F:     include/trace/events/scmi.h
> +F:     include/uapi/linux/virtio_scmi.h
>
>  SYSTEM RESET/SHUTDOWN DRIVERS
>  M:     Sebastian Reichel <[e-mail]>
> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> index e8377b12e4d0..7e9eafdd9b63 100644
> --- a/drivers/firmware/Kconfig
> +++ b/drivers/firmware/Kconfig
> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>           This declares whether a message passing based transport for SCMI is
>           available.
>
> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
> +# this config doesn't show up when SCMI wouldn't be available.
> +config VIRTIO_SCMI
> +       bool "Virtio transport for SCMI"
> +       select ARM_SCMI_HAVE_MSG
> +       depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
> +       help
> +         This enables the virtio based transport for SCMI.
> +
> +         If you want to use the ARM SCMI protocol between the virtio guest and
> +         a host providing a virtio SCMI device, answer Y.
> +
>  config ARM_SCMI_POWER_DOMAIN
>         tristate "SCMI power domain driver"
>         depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> index f6b4acb8abdb..db1787606fb2 100644
> --- a/drivers/firmware/arm_scmi/Makefile
> +++ b/drivers/firmware/arm_scmi/Makefile
> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>                     $(scmi-transport-y)
> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> index 4cb6571c7aaf..bada06cfd33d 100644
> --- a/drivers/firmware/arm_scmi/common.h
> +++ b/drivers/firmware/arm_scmi/common.h
> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>  #ifdef CONFIG_HAVE_ARM_SMCCC
>  extern const struct scmi_desc scmi_smc_desc;
>  #endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +extern const struct scmi_desc scmi_virtio_desc;
> +#endif
>
>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>  void *scmi_get_transport_info(struct device *dev);
> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> index e04e7c8e6928..a31187385470 100644
> --- a/drivers/firmware/arm_scmi/driver.c
> +++ b/drivers/firmware/arm_scmi/driver.c
> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>  #endif
>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>         { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> +#endif
> +#ifdef CONFIG_VIRTIO_SCMI
> +       { .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>  #endif
>         { /* Sentinel */ },
>  };
> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> new file mode 100644
> index 000000000000..20972adf6dc7
> --- /dev/null
> +++ b/drivers/firmware/arm_scmi/virtio.c
> @@ -0,0 +1,523 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Virtio Transport driver for Arm System Control and Management Interface
> + * (SCMI).
> + *
> + * Copyright (C) 2020 OpenSynergy.
> + */
> +
> +/**
> + * DOC: Theory of Operation
> + *
> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
> + *
> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
> + * virtqueue. Access to each virtqueue is protected by spinlocks.
> + */
> +
> +#include <linux/errno.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_config.h>
> +#include <uapi/linux/virtio_ids.h>
> +#include <uapi/linux/virtio_scmi.h>
> +
> +#include "common.h"
> +
> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
> +       (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
> +#define DESCRIPTORS_PER_TX_MSG 2
> +
> +/**
> + * struct scmi_vio_channel - Transport channel information
> + *
> + * @lock: Protects access to all members except ready.
> + * @ready_lock: Protects access to ready. If required, it must be taken before
> + *              lock.
> + * @vqueue: Associated virtqueue
> + * @cinfo: SCMI Tx or Rx channel
> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> + * @is_rx: Whether channel is an Rx channel
> + * @ready: Whether transport user is ready to hear about channel
> + */
> +struct scmi_vio_channel {
> +       spinlock_t lock;
> +       spinlock_t ready_lock;
> +       struct virtqueue *vqueue;
> +       struct scmi_chan_info *cinfo;
> +       struct list_head free_list;
> +       u8 is_rx;
> +       u8 ready;
> +};
> +
> +/**
> + * struct scmi_vio_msg - Transport PDU information
> + *
> + * @request: SDU used for commands
> + * @input: SDU used for (delayed) responses and notifications
> + * @list: List which scmi_vio_msg may be part of
> + * @rx_len: Input SDU size in bytes, once input has been received
> + */
> +struct scmi_vio_msg {
> +       struct scmi_msg_payld *request;
> +       struct scmi_msg_payld *input;
> +       struct list_head list;
> +       unsigned int rx_len;
> +};
> +
> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> +{
> +       return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> +}
> +
> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> +                              struct scmi_vio_msg *msg)
> +{
> +       struct scatterlist sg_in;
> +       int rc;
> +       unsigned long flags;
> +
> +       sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
> +
> +       spin_lock_irqsave(&vioch->lock, flags);
> +
> +       rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
> +       if (rc)
> +               dev_err_once(vioch->cinfo->dev,
> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
> +                            rc);
> +       else
> +               virtqueue_kick(vioch->vqueue);
> +
> +       spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +       return rc;
> +}
> +
> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> +{
> +       unsigned long ready_flags;
> +       unsigned long flags;
> +       unsigned int length;
> +       struct scmi_vio_channel *vioch;
> +       struct scmi_vio_msg *msg;
> +       bool cb_enabled = true;
> +
> +       if (WARN_ON_ONCE(!vqueue->vdev->priv))
> +               return;
> +       vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
> +
> +       for (;;) {
> +               spin_lock_irqsave(&vioch->ready_lock, ready_flags);
> +
> +               if (!vioch->ready) {
> +                       if (!cb_enabled)
> +                               (void)virtqueue_enable_cb(vqueue);
> +                       goto unlock_ready_out;
> +               }
> +
> +               spin_lock_irqsave(&vioch->lock, flags);
> +               if (cb_enabled) {
> +                       virtqueue_disable_cb(vqueue);
> +                       cb_enabled = false;
> +               }
> +               msg = virtqueue_get_buf(vqueue, &length);
> +               if (!msg) {
> +                       if (virtqueue_enable_cb(vqueue))
> +                               goto unlock_out;
> +                       else
> +                               cb_enabled = true;
> +               }
> +               spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +               if (msg) {
> +                       msg->rx_len = length;
> +
> +                       /*
> +                        * Hold the ready_lock during the callback to avoid
> +                        * races when the arm-scmi driver is unbinding while
> +                        * the virtio device is not quiesced yet.
> +                        */
> +                       scmi_rx_callback(vioch->cinfo,
> +                                        msg_read_header(msg->input), msg);
> +               }
> +               spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +       }
> +
> +unlock_out:
> +       spin_unlock_irqrestore(&vioch->lock, flags);
> +unlock_ready_out:
> +       spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> +}
> +
> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
> +
> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
> +       scmi_vio_complete_cb,
> +       scmi_vio_complete_cb
> +};
> +
> +static unsigned int virtio_get_max_msg(bool tx,
> +                                      struct scmi_chan_info *base_cinfo)
> +{
> +       struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> +       unsigned int ret;
> +
> +       ret = virtqueue_get_vring_size(vioch->vqueue);
> +
> +       /* Tx messages need multiple descriptors. */()
> +       if (tx)
> +               ret /= DESCRIPTORS_PER_TX_MSG;
> +
> +       if (ret > MSG_TOKEN_MAX) {

__scmi_xfer_info_init() returns error for info->max_msg >=
MSG_TOKEN_MAX so it should be (ret >= MSG_TOKEN_MAX


> +               dev_info_once(
> +                       base_cinfo->dev,
> +                       "Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> +                       MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> +               ret = MSG_TOKEN_MAX;

should be ret = MSG_TOKEN_MAX-1;

> +       }
> +
> +       return ret;
> +}
> +
> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> +{
> +       return 1;
> +}
> +
> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> +
> +static int virtio_link_supplier(struct device *dev)
> +{
> +       struct device *vdev = driver_find_device(
> +               &virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> +
> +       if (!vdev) {
> +               dev_notice_once(
> +                       dev,
> +                       "Deferring probe after not finding a bound scmi-virtio device\n");
> +               return -EPROBE_DEFER;
> +       }
> +
> +       /* Add device link for remove order and sysfs link. */
> +       if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> +               put_device(vdev);
> +               dev_err(dev, "Adding link to supplier virtio device failed\n");
> +               return -ECANCELED;
> +       }
> +
> +       put_device(vdev);
> +       return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> +}
> +
> +static bool virtio_chan_available(struct device *dev, int idx)
> +{
> +       struct virtio_device *vdev;
> +
> +       /* scmi-virtio doesn't support per-protocol channels */
> +       if (is_scmi_protocol_device(dev))
> +               return false;
> +
> +       vdev = scmi_get_transport_info(dev);
> +       if (!vdev)
> +               return false;
> +
> +       switch (idx) {
> +       case VIRTIO_SCMI_VQ_TX:
> +               return true;
> +       case VIRTIO_SCMI_VQ_RX:
> +               return scmi_vio_have_vq_rx(vdev);
> +       default:
> +               return false;
> +       }
> +}
> +
> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> +                            bool tx)
> +{
> +       unsigned long flags;
> +       struct virtio_device *vdev;
> +       struct scmi_vio_channel *vioch;
> +       int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> +       int max_msg;
> +       int i;
> +
> +       if (!virtio_chan_available(dev, index))
> +               return -ENODEV;
> +
> +       vdev = scmi_get_transport_info(dev);
> +       vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> +
> +       spin_lock_irqsave(&vioch->lock, flags);
> +       cinfo->transport_info = vioch;
> +       vioch->cinfo = cinfo;
> +       spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +       max_msg = virtio_get_max_msg(tx, cinfo);
> +
> +       for (i = 0; i < max_msg; i++) {
> +               struct scmi_vio_msg *msg;
> +
> +               msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> +               if (!msg)
> +                       return -ENOMEM;
> +
> +               if (tx) {
> +                       msg->request = devm_kzalloc(cinfo->dev,
> +                                                   VIRTIO_SCMI_MAX_PDU_SIZE,
> +                                                   GFP_KERNEL);
> +                       if (!msg->request)
> +                               return -ENOMEM;
> +               }
> +
> +               msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> +                                         GFP_KERNEL);
> +               if (!msg->input)
> +                       return -ENOMEM;
> +
> +               if (tx) {
> +                       spin_lock_irqsave(&vioch->lock, flags);
> +                       list_add_tail(&msg->list, &vioch->free_list);
> +                       spin_unlock_irqrestore(&vioch->lock, flags);
> +               } else {
> +                       scmi_vio_feed_vq_rx(vioch, msg);
> +               }
> +       }
> +
> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> +       vioch->ready = true;
> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +       return 0;
> +}
> +
> +static int virtio_chan_free(int id, void *p, void *data)
> +{
> +       unsigned long flags;
> +       struct scmi_chan_info *cinfo = p;
> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> +       vioch->ready = false;
> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> +
> +       scmi_free_channel(cinfo, data, id);
> +       return 0;
> +}
> +
> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> +                              struct scmi_xfer *xfer)
> +{
> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> +       struct scatterlist sg_out;
> +       struct scatterlist sg_in;
> +       struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> +       unsigned long flags;
> +       int rc;
> +       struct scmi_vio_msg *msg;
> +
> +       /*
> +        * TODO: For now, we don't support polling. But it should not be
> +        * difficult to add support.
> +        */
> +       if (xfer->hdr.poll_completion)
> +               return -EINVAL;
> +
> +       spin_lock_irqsave(&vioch->lock, flags);
> +
> +       if (list_empty(&vioch->free_list)) {
> +               spin_unlock_irqrestore(&vioch->lock, flags);
> +               return -EBUSY;
> +       }
> +
> +       msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> +       list_del(&msg->list);
> +
> +       msg_tx_prepare(msg->request, xfer);
> +
> +       sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> +       sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> +
> +       rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> +       if (rc) {
> +               list_add(&msg->list, &vioch->free_list);
> +               dev_err_once(vioch->cinfo->dev,
> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
> +                            rc);
> +       } else {
> +               virtqueue_kick(vioch->vqueue);
> +       }
> +
> +       spin_unlock_irqrestore(&vioch->lock, flags);
> +
> +       return rc;
> +}
> +
> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> +                                 struct scmi_xfer *xfer, void *msg_handle)
> +{
> +       struct scmi_vio_msg *msg = msg_handle;
> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +       if (!msg) {
> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> +                            "Ignoring %s() call with NULL msg_handle\n",
> +                            __func__);
> +               return;
> +       }
> +
> +       msg_fetch_response(msg->input, msg->rx_len, xfer);
> +}
> +
> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> +                                     size_t max_len, struct scmi_xfer *xfer,
> +                                     void *msg_handle)
> +{
> +       struct scmi_vio_msg *msg = msg_handle;
> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> +
> +       if (!msg) {
> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> +                            "Ignoring %s() call with NULL msg_handle\n",
> +                            __func__);
> +               return;
> +       }
> +
> +       msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> +}
> +
> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> +{
> +}
> +
> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> +                           struct scmi_xfer *xfer)
> +{
> +       return false;
> +}
> +
> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> +{
> +       unsigned long flags;
> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> +       struct scmi_vio_msg *msg = msg_handle;
> +
> +       if (!msg) {
> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> +                            "Ignoring %s() call with NULL msg_handle\n",
> +                            __func__);
> +               return;
> +       }
> +
> +       if (vioch->is_rx) {
> +               scmi_vio_feed_vq_rx(vioch, msg);
> +       } else {
> +               spin_lock_irqsave(&vioch->lock, flags);
> +               list_add(&msg->list, &vioch->free_list);
> +               spin_unlock_irqrestore(&vioch->lock, flags);
> +       }
> +}
> +
> +static const struct scmi_transport_ops scmi_virtio_ops = {
> +       .link_supplier = virtio_link_supplier,
> +       .chan_available = virtio_chan_available,
> +       .chan_setup = virtio_chan_setup,
> +       .chan_free = virtio_chan_free,
> +       .get_max_msg = virtio_get_max_msg,
> +       .send_message = virtio_send_message,
> +       .fetch_response = virtio_fetch_response,
> +       .fetch_notification = virtio_fetch_notification,
> +       .clear_channel = dummy_clear_channel,
> +       .poll_done = dummy_poll_done,
> +       .drop_message = virtio_drop_message,
> +};
> +
> +static int scmi_vio_probe(struct virtio_device *vdev)
> +{
> +       struct device *dev = &vdev->dev;
> +       struct scmi_vio_channel *channels;
> +       bool have_vq_rx;
> +       int vq_cnt;
> +       int i;
> +       int ret;
> +       struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> +
> +       have_vq_rx = scmi_vio_have_vq_rx(vdev);
> +       vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> +
> +       channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> +       if (!channels)
> +               return -ENOMEM;
> +
> +       if (have_vq_rx)
> +               channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> +
> +       ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> +                             scmi_vio_vqueue_names, NULL);
> +       if (ret) {
> +               dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> +               return ret;
> +       }
> +       dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> +
> +       for (i = 0; i < vq_cnt; i++) {
> +               spin_lock_init(&channels[i].lock);
> +               spin_lock_init(&channels[i].ready_lock);
> +               INIT_LIST_HEAD(&channels[i].free_list);
> +               channels[i].vqueue = vqs[i];
> +       }
> +
> +       vdev->priv = channels;
> +
> +       return 0;
> +}
> +
> +static void scmi_vio_remove(struct virtio_device *vdev)
> +{
> +       vdev->config->reset(vdev);
> +       vdev->config->del_vqs(vdev);
> +}
> +
> +static unsigned int features[] = {
> +       VIRTIO_SCMI_F_P2A_CHANNELS,
> +};
> +
> +static const struct virtio_device_id id_table[] = {
> +       { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> +       { 0 }
> +};
> +
> +static struct virtio_driver virtio_scmi_driver = {
> +       .driver.name = "scmi-virtio",
> +       .driver.owner = THIS_MODULE,
> +       .feature_table = features,
> +       .feature_table_size = ARRAY_SIZE(features),
> +       .id_table = id_table,
> +       .probe = scmi_vio_probe,
> +       .remove = scmi_vio_remove,
> +};
> +
> +static int __init virtio_scmi_init(void)
> +{
> +       return register_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +static void __exit virtio_scmi_exit(void)
> +{
> +       unregister_virtio_driver(&virtio_scmi_driver);
> +}
> +
> +const struct scmi_desc scmi_virtio_desc = {
> +       .init = virtio_scmi_init,
> +       .exit = virtio_scmi_exit,
> +       .ops = &scmi_virtio_ops,
> +       .max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> +       .max_msg = 0, /* overridden by virtio_get_max_msg() */
> +       .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> +};
> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> index f0c35ce8628c..c146fe30e589 100644
> --- a/include/uapi/linux/virtio_ids.h
> +++ b/include/uapi/linux/virtio_ids.h
> @@ -56,5 +56,6 @@
>  #define VIRTIO_ID_PMEM                 27 /* virtio pmem */
>  #define VIRTIO_ID_BT                   28 /* virtio bluetooth */
>  #define VIRTIO_ID_MAC80211_HWSIM       29 /* virtio mac80211-hwsim */
> +#define VIRTIO_ID_SCMI                 32 /* virtio SCMI */
>
>  #endif /* _LINUX_VIRTIO_IDS_H */
> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> new file mode 100644
> index 000000000000..732b01504c35
> --- /dev/null
> +++ b/include/uapi/linux/virtio_scmi.h
> @@ -0,0 +1,25 @@
> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> +/*
> + * Copyright (C) 2020 OpenSynergy GmbH
> + */
> +
> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> +
> +#include <linux/virtio_types.h>
> +
> +/* Feature bits */
> +
> +/* Device implements some SCMI notifications, or delayed responses. */
> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> +
> +/* Device implements any SCMI statistics shared memory region */
> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> +
> +/* Virtqueues */
> +
> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> +
> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> --
> 2.25.1
>
>

Peter Hilber June 2, 2021, 8:25 a.m. UTC | #4

On 01.06.21 16:53, Vincent Guittot wrote:
> On Tue, 11 May 2021 at 02:28, Peter Hilber <[e-mail]> wrote:
>>
>> From: Igor Skalkin <[e-mail]>
>>
>> This transport enables accessing an SCMI platform as a virtio device.
>>
>> Implement an SCMI virtio driver according to the virtio SCMI device spec
>> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
>>
>> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
>> at most one Rx channel (virtio eventq, P2A channel).
>>
>> The following feature bit defined in [1] is not implemented:
>> VIRTIO_SCMI_F_SHARED_MEMORY.
>>
>> After the preparatory patches, this implements the virtio transport as
>> paraphrased:
>>
>> Only support a single arm-scmi device (which is consistent with the SCMI
>> spec). scmi-virtio init is called from arm-scmi module init. During the
>> arm-scmi probing, link to the first probed scmi-virtio device. Defer
>> arm-scmi probing if no scmi-virtio device is bound yet.
>>
>> For simplicity, restrict the number of messages which can be pending
>> simultaneously according to the virtqueue capacity. (The virtqueue sizes
>> are negotiated with the virtio device.)
>>
>> As soon as Rx channel message buffers are allocated or have been read
>> out by the arm-scmi driver, feed them to the virtio device.
>>
>> Since some virtio devices may not have the short response time exhibited
>> by SCMI platforms using other transports, set a generous response
>> timeout.
>>
>> Limitations:
>>
>> - Polling is not supported.
>>
>> - The timeout for delayed responses has not been adjusted.
>>
>> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
>> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
>>
>> Signed-off-by: Igor Skalkin <[e-mail]>
>> [ Peter: Adapted patch for submission to upstream. ]
>> Co-developed-by: Peter Hilber <[e-mail]>
>> Signed-off-by: Peter Hilber <[e-mail]>
>> ---
>>  MAINTAINERS                        |   1 +
>>  drivers/firmware/Kconfig           |  12 +
>>  drivers/firmware/arm_scmi/Makefile |   1 +
>>  drivers/firmware/arm_scmi/common.h |   3 +
>>  drivers/firmware/arm_scmi/driver.c |   3 +
>>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>>  include/uapi/linux/virtio_ids.h    |   1 +
>>  include/uapi/linux/virtio_scmi.h   |  25 ++
>>  8 files changed, 569 insertions(+)
>>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>>  create mode 100644 include/uapi/linux/virtio_scmi.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index bd7aff0c120f..449c336872f3 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -17705,6 +17705,7 @@ F:      drivers/regulator/scmi-regulator.c
>>  F:     drivers/reset/reset-scmi.c
>>  F:     include/linux/sc[mp]i_protocol.h
>>  F:     include/trace/events/scmi.h
>> +F:     include/uapi/linux/virtio_scmi.h
>>
>>  SYSTEM RESET/SHUTDOWN DRIVERS
>>  M:     Sebastian Reichel <[e-mail]>
>> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
>> index e8377b12e4d0..7e9eafdd9b63 100644
>> --- a/drivers/firmware/Kconfig
>> +++ b/drivers/firmware/Kconfig
>> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>>           This declares whether a message passing based transport for SCMI is
>>           available.
>>
>> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
>> +# this config doesn't show up when SCMI wouldn't be available.
>> +config VIRTIO_SCMI
>> +       bool "Virtio transport for SCMI"
>> +       select ARM_SCMI_HAVE_MSG
>> +       depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
>> +       help
>> +         This enables the virtio based transport for SCMI.
>> +
>> +         If you want to use the ARM SCMI protocol between the virtio guest and
>> +         a host providing a virtio SCMI device, answer Y.
>> +
>>  config ARM_SCMI_POWER_DOMAIN
>>         tristate "SCMI power domain driver"
>>         depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
>> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
>> index f6b4acb8abdb..db1787606fb2 100644
>> --- a/drivers/firmware/arm_scmi/Makefile
>> +++ b/drivers/firmware/arm_scmi/Makefile
>> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
>> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>>                     $(scmi-transport-y)
>> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
>> index 4cb6571c7aaf..bada06cfd33d 100644
>> --- a/drivers/firmware/arm_scmi/common.h
>> +++ b/drivers/firmware/arm_scmi/common.h
>> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>>  #ifdef CONFIG_HAVE_ARM_SMCCC
>>  extern const struct scmi_desc scmi_smc_desc;
>>  #endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +extern const struct scmi_desc scmi_virtio_desc;
>> +#endif
>>
>>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>>  void *scmi_get_transport_info(struct device *dev);
>> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
>> index e04e7c8e6928..a31187385470 100644
>> --- a/drivers/firmware/arm_scmi/driver.c
>> +++ b/drivers/firmware/arm_scmi/driver.c
>> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>>  #endif
>>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>>         { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
>> +#endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +       { .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>>  #endif
>>         { /* Sentinel */ },
>>  };
>> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
>> new file mode 100644
>> index 000000000000..20972adf6dc7
>> --- /dev/null
>> +++ b/drivers/firmware/arm_scmi/virtio.c
>> @@ -0,0 +1,523 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Virtio Transport driver for Arm System Control and Management Interface
>> + * (SCMI).
>> + *
>> + * Copyright (C) 2020 OpenSynergy.
>> + */
>> +
>> +/**
>> + * DOC: Theory of Operation
>> + *
>> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
>> + *
>> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
>> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
>> + * virtqueue. Access to each virtqueue is protected by spinlocks.
>> + */
>> +
>> +#include <linux/errno.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/module.h>
>> +#include <linux/slab.h>
>> +#include <linux/virtio.h>
>> +#include <linux/virtio_config.h>
>> +#include <uapi/linux/virtio_ids.h>
>> +#include <uapi/linux/virtio_scmi.h>
>> +
>> +#include "common.h"
>> +
>> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
>> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
>> +       (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
>> +#define DESCRIPTORS_PER_TX_MSG 2
>> +
>> +/**
>> + * struct scmi_vio_channel - Transport channel information
>> + *
>> + * @lock: Protects access to all members except ready.
>> + * @ready_lock: Protects access to ready. If required, it must be taken before
>> + *              lock.
>> + * @vqueue: Associated virtqueue
>> + * @cinfo: SCMI Tx or Rx channel
>> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
>> + * @is_rx: Whether channel is an Rx channel
>> + * @ready: Whether transport user is ready to hear about channel
>> + */
>> +struct scmi_vio_channel {
>> +       spinlock_t lock;
>> +       spinlock_t ready_lock;
>> +       struct virtqueue *vqueue;
>> +       struct scmi_chan_info *cinfo;
>> +       struct list_head free_list;
>> +       u8 is_rx;
>> +       u8 ready;
>> +};
>> +
>> +/**
>> + * struct scmi_vio_msg - Transport PDU information
>> + *
>> + * @request: SDU used for commands
>> + * @input: SDU used for (delayed) responses and notifications
>> + * @list: List which scmi_vio_msg may be part of
>> + * @rx_len: Input SDU size in bytes, once input has been received
>> + */
>> +struct scmi_vio_msg {
>> +       struct scmi_msg_payld *request;
>> +       struct scmi_msg_payld *input;
>> +       struct list_head list;
>> +       unsigned int rx_len;
>> +};
>> +
>> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
>> +{
>> +       return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
>> +}
>> +
>> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
>> +                              struct scmi_vio_msg *msg)
>> +{
>> +       struct scatterlist sg_in;
>> +       int rc;
>> +       unsigned long flags;
>> +
>> +       sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
>> +
>> +       spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +       rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
>> +       if (rc)
>> +               dev_err_once(vioch->cinfo->dev,
>> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
>> +                            rc);
>> +       else
>> +               virtqueue_kick(vioch->vqueue);
>> +
>> +       spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +       return rc;
>> +}
>> +
>> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
>> +{
>> +       unsigned long ready_flags;
>> +       unsigned long flags;
>> +       unsigned int length;
>> +       struct scmi_vio_channel *vioch;
>> +       struct scmi_vio_msg *msg;
>> +       bool cb_enabled = true;
>> +
>> +       if (WARN_ON_ONCE(!vqueue->vdev->priv))
>> +               return;
>> +       vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
>> +
>> +       for (;;) {
>> +               spin_lock_irqsave(&vioch->ready_lock, ready_flags);
>> +
>> +               if (!vioch->ready) {
>> +                       if (!cb_enabled)
>> +                               (void)virtqueue_enable_cb(vqueue);
>> +                       goto unlock_ready_out;
>> +               }
>> +
>> +               spin_lock_irqsave(&vioch->lock, flags);
>> +               if (cb_enabled) {
>> +                       virtqueue_disable_cb(vqueue);
>> +                       cb_enabled = false;
>> +               }
>> +               msg = virtqueue_get_buf(vqueue, &length);
>> +               if (!msg) {
>> +                       if (virtqueue_enable_cb(vqueue))
>> +                               goto unlock_out;
>> +                       else
>> +                               cb_enabled = true;
>> +               }
>> +               spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +               if (msg) {
>> +                       msg->rx_len = length;
>> +
>> +                       /*
>> +                        * Hold the ready_lock during the callback to avoid
>> +                        * races when the arm-scmi driver is unbinding while
>> +                        * the virtio device is not quiesced yet.
>> +                        */
>> +                       scmi_rx_callback(vioch->cinfo,
>> +                                        msg_read_header(msg->input), msg);
>> +               }
>> +               spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +       }
>> +
>> +unlock_out:
>> +       spin_unlock_irqrestore(&vioch->lock, flags);
>> +unlock_ready_out:
>> +       spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +}
>> +
>> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
>> +
>> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
>> +       scmi_vio_complete_cb,
>> +       scmi_vio_complete_cb
>> +};
>> +
>> +static unsigned int virtio_get_max_msg(bool tx,
>> +                                      struct scmi_chan_info *base_cinfo)
>> +{
>> +       struct scmi_vio_channel *vioch = base_cinfo->transport_info;
>> +       unsigned int ret;
>> +
>> +       ret = virtqueue_get_vring_size(vioch->vqueue);
>> +
>> +       /* Tx messages need multiple descriptors. */()
>> +       if (tx)
>> +               ret /= DESCRIPTORS_PER_TX_MSG;
>> +
>> +       if (ret > MSG_TOKEN_MAX) {
> 
> __scmi_xfer_info_init() returns error for info->max_msg >=
> MSG_TOKEN_MAX so it should be (ret >= MSG_TOKEN_MAX
> 

I think it would be better to use the > comparison in
__scmi_xfer_info_init(), too. That should work in my understanding. I
think that change was originally in my branch, but I lost it somehow.

> 
>> +               dev_info_once(
>> +                       base_cinfo->dev,
>> +                       "Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
>> +                       MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
>> +               ret = MSG_TOKEN_MAX;
> 
> should be ret = MSG_TOKEN_MAX-1;
> 
>> +       }
>> +
>> +       return ret;
>> +}
>> +
>> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
>> +{
>> +       return 1;
>> +}
>> +
>> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
>> +
>> +static int virtio_link_supplier(struct device *dev)
>> +{
>> +       struct device *vdev = driver_find_device(
>> +               &virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
>> +
>> +       if (!vdev) {
>> +               dev_notice_once(
>> +                       dev,
>> +                       "Deferring probe after not finding a bound scmi-virtio device\n");
>> +               return -EPROBE_DEFER;
>> +       }
>> +
>> +       /* Add device link for remove order and sysfs link. */
>> +       if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
>> +               put_device(vdev);
>> +               dev_err(dev, "Adding link to supplier virtio device failed\n");
>> +               return -ECANCELED;
>> +       }
>> +
>> +       put_device(vdev);
>> +       return scmi_set_transport_info(dev, dev_to_virtio(vdev));
>> +}
>> +
>> +static bool virtio_chan_available(struct device *dev, int idx)
>> +{
>> +       struct virtio_device *vdev;
>> +
>> +       /* scmi-virtio doesn't support per-protocol channels */
>> +       if (is_scmi_protocol_device(dev))
>> +               return false;
>> +
>> +       vdev = scmi_get_transport_info(dev);
>> +       if (!vdev)
>> +               return false;
>> +
>> +       switch (idx) {
>> +       case VIRTIO_SCMI_VQ_TX:
>> +               return true;
>> +       case VIRTIO_SCMI_VQ_RX:
>> +               return scmi_vio_have_vq_rx(vdev);
>> +       default:
>> +               return false;
>> +       }
>> +}
>> +
>> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>> +                            bool tx)
>> +{
>> +       unsigned long flags;
>> +       struct virtio_device *vdev;
>> +       struct scmi_vio_channel *vioch;
>> +       int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
>> +       int max_msg;
>> +       int i;
>> +
>> +       if (!virtio_chan_available(dev, index))
>> +               return -ENODEV;
>> +
>> +       vdev = scmi_get_transport_info(dev);
>> +       vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
>> +
>> +       spin_lock_irqsave(&vioch->lock, flags);
>> +       cinfo->transport_info = vioch;
>> +       vioch->cinfo = cinfo;
>> +       spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +       max_msg = virtio_get_max_msg(tx, cinfo);
>> +
>> +       for (i = 0; i < max_msg; i++) {
>> +               struct scmi_vio_msg *msg;
>> +
>> +               msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
>> +               if (!msg)
>> +                       return -ENOMEM;
>> +
>> +               if (tx) {
>> +                       msg->request = devm_kzalloc(cinfo->dev,
>> +                                                   VIRTIO_SCMI_MAX_PDU_SIZE,
>> +                                                   GFP_KERNEL);
>> +                       if (!msg->request)
>> +                               return -ENOMEM;
>> +               }
>> +
>> +               msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
>> +                                         GFP_KERNEL);
>> +               if (!msg->input)
>> +                       return -ENOMEM;
>> +
>> +               if (tx) {
>> +                       spin_lock_irqsave(&vioch->lock, flags);
>> +                       list_add_tail(&msg->list, &vioch->free_list);
>> +                       spin_unlock_irqrestore(&vioch->lock, flags);
>> +               } else {
>> +                       scmi_vio_feed_vq_rx(vioch, msg);
>> +               }
>> +       }
>> +
>> +       spin_lock_irqsave(&vioch->ready_lock, flags);
>> +       vioch->ready = true;
>> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +       return 0;
>> +}
>> +
>> +static int virtio_chan_free(int id, void *p, void *data)
>> +{
>> +       unsigned long flags;
>> +       struct scmi_chan_info *cinfo = p;
>> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +       spin_lock_irqsave(&vioch->ready_lock, flags);
>> +       vioch->ready = false;
>> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +       scmi_free_channel(cinfo, data, id);
>> +       return 0;
>> +}
>> +
>> +static int virtio_send_message(struct scmi_chan_info *cinfo,
>> +                              struct scmi_xfer *xfer)
>> +{
>> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +       struct scatterlist sg_out;
>> +       struct scatterlist sg_in;
>> +       struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
>> +       unsigned long flags;
>> +       int rc;
>> +       struct scmi_vio_msg *msg;
>> +
>> +       /*
>> +        * TODO: For now, we don't support polling. But it should not be
>> +        * difficult to add support.
>> +        */
>> +       if (xfer->hdr.poll_completion)
>> +               return -EINVAL;
>> +
>> +       spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +       if (list_empty(&vioch->free_list)) {
>> +               spin_unlock_irqrestore(&vioch->lock, flags);
>> +               return -EBUSY;
>> +       }
>> +
>> +       msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
>> +       list_del(&msg->list);
>> +
>> +       msg_tx_prepare(msg->request, xfer);
>> +
>> +       sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
>> +       sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
>> +
>> +       rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
>> +       if (rc) {
>> +               list_add(&msg->list, &vioch->free_list);
>> +               dev_err_once(vioch->cinfo->dev,
>> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
>> +                            rc);
>> +       } else {
>> +               virtqueue_kick(vioch->vqueue);
>> +       }
>> +
>> +       spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +       return rc;
>> +}
>> +
>> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
>> +                                 struct scmi_xfer *xfer, void *msg_handle)
>> +{
>> +       struct scmi_vio_msg *msg = msg_handle;
>> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +       if (!msg) {
>> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +                            "Ignoring %s() call with NULL msg_handle\n",
>> +                            __func__);
>> +               return;
>> +       }
>> +
>> +       msg_fetch_response(msg->input, msg->rx_len, xfer);
>> +}
>> +
>> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
>> +                                     size_t max_len, struct scmi_xfer *xfer,
>> +                                     void *msg_handle)
>> +{
>> +       struct scmi_vio_msg *msg = msg_handle;
>> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +       if (!msg) {
>> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +                            "Ignoring %s() call with NULL msg_handle\n",
>> +                            __func__);
>> +               return;
>> +       }
>> +
>> +       msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
>> +}
>> +
>> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
>> +{
>> +}
>> +
>> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
>> +                           struct scmi_xfer *xfer)
>> +{
>> +       return false;
>> +}
>> +
>> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
>> +{
>> +       unsigned long flags;
>> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +       struct scmi_vio_msg *msg = msg_handle;
>> +
>> +       if (!msg) {
>> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +                            "Ignoring %s() call with NULL msg_handle\n",
>> +                            __func__);
>> +               return;
>> +       }
>> +
>> +       if (vioch->is_rx) {
>> +               scmi_vio_feed_vq_rx(vioch, msg);
>> +       } else {
>> +               spin_lock_irqsave(&vioch->lock, flags);
>> +               list_add(&msg->list, &vioch->free_list);
>> +               spin_unlock_irqrestore(&vioch->lock, flags);
>> +       }
>> +}
>> +
>> +static const struct scmi_transport_ops scmi_virtio_ops = {
>> +       .link_supplier = virtio_link_supplier,
>> +       .chan_available = virtio_chan_available,
>> +       .chan_setup = virtio_chan_setup,
>> +       .chan_free = virtio_chan_free,
>> +       .get_max_msg = virtio_get_max_msg,
>> +       .send_message = virtio_send_message,
>> +       .fetch_response = virtio_fetch_response,
>> +       .fetch_notification = virtio_fetch_notification,
>> +       .clear_channel = dummy_clear_channel,
>> +       .poll_done = dummy_poll_done,
>> +       .drop_message = virtio_drop_message,
>> +};
>> +
>> +static int scmi_vio_probe(struct virtio_device *vdev)
>> +{
>> +       struct device *dev = &vdev->dev;
>> +       struct scmi_vio_channel *channels;
>> +       bool have_vq_rx;
>> +       int vq_cnt;
>> +       int i;
>> +       int ret;
>> +       struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
>> +
>> +       have_vq_rx = scmi_vio_have_vq_rx(vdev);
>> +       vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
>> +
>> +       channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
>> +       if (!channels)
>> +               return -ENOMEM;
>> +
>> +       if (have_vq_rx)
>> +               channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
>> +
>> +       ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
>> +                             scmi_vio_vqueue_names, NULL);
>> +       if (ret) {
>> +               dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
>> +               return ret;
>> +       }
>> +       dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
>> +
>> +       for (i = 0; i < vq_cnt; i++) {
>> +               spin_lock_init(&channels[i].lock);
>> +               spin_lock_init(&channels[i].ready_lock);
>> +               INIT_LIST_HEAD(&channels[i].free_list);
>> +               channels[i].vqueue = vqs[i];
>> +       }
>> +
>> +       vdev->priv = channels;
>> +
>> +       return 0;
>> +}
>> +
>> +static void scmi_vio_remove(struct virtio_device *vdev)
>> +{
>> +       vdev->config->reset(vdev);
>> +       vdev->config->del_vqs(vdev);
>> +}
>> +
>> +static unsigned int features[] = {
>> +       VIRTIO_SCMI_F_P2A_CHANNELS,
>> +};
>> +
>> +static const struct virtio_device_id id_table[] = {
>> +       { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
>> +       { 0 }
>> +};
>> +
>> +static struct virtio_driver virtio_scmi_driver = {
>> +       .driver.name = "scmi-virtio",
>> +       .driver.owner = THIS_MODULE,
>> +       .feature_table = features,
>> +       .feature_table_size = ARRAY_SIZE(features),
>> +       .id_table = id_table,
>> +       .probe = scmi_vio_probe,
>> +       .remove = scmi_vio_remove,
>> +};
>> +
>> +static int __init virtio_scmi_init(void)
>> +{
>> +       return register_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +static void __exit virtio_scmi_exit(void)
>> +{
>> +       unregister_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +const struct scmi_desc scmi_virtio_desc = {
>> +       .init = virtio_scmi_init,
>> +       .exit = virtio_scmi_exit,
>> +       .ops = &scmi_virtio_ops,
>> +       .max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
>> +       .max_msg = 0, /* overridden by virtio_get_max_msg() */
>> +       .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
>> +};
>> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
>> index f0c35ce8628c..c146fe30e589 100644
>> --- a/include/uapi/linux/virtio_ids.h
>> +++ b/include/uapi/linux/virtio_ids.h
>> @@ -56,5 +56,6 @@
>>  #define VIRTIO_ID_PMEM                 27 /* virtio pmem */
>>  #define VIRTIO_ID_BT                   28 /* virtio bluetooth */
>>  #define VIRTIO_ID_MAC80211_HWSIM       29 /* virtio mac80211-hwsim */
>> +#define VIRTIO_ID_SCMI                 32 /* virtio SCMI */
>>
>>  #endif /* _LINUX_VIRTIO_IDS_H */
>> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
>> new file mode 100644
>> index 000000000000..732b01504c35
>> --- /dev/null
>> +++ b/include/uapi/linux/virtio_scmi.h
>> @@ -0,0 +1,25 @@
>> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
>> +/*
>> + * Copyright (C) 2020 OpenSynergy GmbH
>> + */
>> +
>> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
>> +#define _UAPI_LINUX_VIRTIO_SCMI_H
>> +
>> +#include <linux/virtio_types.h>
>> +
>> +/* Feature bits */
>> +
>> +/* Device implements some SCMI notifications, or delayed responses. */
>> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
>> +
>> +/* Device implements any SCMI statistics shared memory region */
>> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
>> +
>> +/* Virtqueues */
>> +
>> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
>> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
>> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
>> +
>> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
>> --
>> 2.25.1
>>
>>
>

Cristian Marussi June 2, 2021, 8:33 a.m. UTC | #5

Hi,

On Wed, Jun 02, 2021 at 10:25:36AM +0200, Peter Hilber wrote:
> On 01.06.21 16:53, Vincent Guittot wrote:
> > On Tue, 11 May 2021 at 02:28, Peter Hilber <[e-mail]> wrote:
> >>
> >> From: Igor Skalkin <[e-mail]>
> >>
> >> This transport enables accessing an SCMI platform as a virtio device.
> >>
> >> Implement an SCMI virtio driver according to the virtio SCMI device spec
> >> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
> >>
> >> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> >> at most one Rx channel (virtio eventq, P2A channel).
> >>
> >> The following feature bit defined in [1] is not implemented:
> >> VIRTIO_SCMI_F_SHARED_MEMORY.
> >>
> >> After the preparatory patches, this implements the virtio transport as
> >> paraphrased:
> >>
> >> Only support a single arm-scmi device (which is consistent with the SCMI
> >> spec). scmi-virtio init is called from arm-scmi module init. During the
> >> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> >> arm-scmi probing if no scmi-virtio device is bound yet.
> >>
> >> For simplicity, restrict the number of messages which can be pending
> >> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> >> are negotiated with the virtio device.)
> >>
> >> As soon as Rx channel message buffers are allocated or have been read
> >> out by the arm-scmi driver, feed them to the virtio device.
> >>
> >> Since some virtio devices may not have the short response time exhibited
> >> by SCMI platforms using other transports, set a generous response
> >> timeout.
> >>
> >> Limitations:
> >>
> >> - Polling is not supported.
> >>
> >> - The timeout for delayed responses has not been adjusted.
> >>
> >> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> >> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
> >>
> >> Signed-off-by: Igor Skalkin <[e-mail]>
> >> [ Peter: Adapted patch for submission to upstream. ]
> >> Co-developed-by: Peter Hilber <[e-mail]>
> >> Signed-off-by: Peter Hilber <[e-mail]>

[snip]

> >> +
> >> +static unsigned int virtio_get_max_msg(bool tx,
> >> +                                      struct scmi_chan_info *base_cinfo)
> >> +{
> >> +       struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> >> +       unsigned int ret;
> >> +
> >> +       ret = virtqueue_get_vring_size(vioch->vqueue);
> >> +
> >> +       /* Tx messages need multiple descriptors. */()
> >> +       if (tx)
> >> +               ret /= DESCRIPTORS_PER_TX_MSG;
> >> +
> >> +       if (ret > MSG_TOKEN_MAX) {
> > 
> > __scmi_xfer_info_init() returns error for info->max_msg >=
> > MSG_TOKEN_MAX so it should be (ret >= MSG_TOKEN_MAX
> > 
> 
> I think it would be better to use the > comparison in
> __scmi_xfer_info_init(), too. That should work in my understanding. I
> think that change was originally in my branch, but I lost it somehow.
> 

I'll include this proposed fixes on my temp rework for V4.

Thanks,
Cristian

> > 
> >> +               dev_info_once(
> >> +                       base_cinfo->dev,
> >> +                       "Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> >> +                       MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> >> +               ret = MSG_TOKEN_MAX;
> > 
> > should be ret = MSG_TOKEN_MAX-1;
> > 
> >> +       }
> >> +
> >> +       return ret;
> >> +}
> >> +
> >> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> >> +{
> >> +       return 1;
> >> +}
> >> +
> >> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> >> +
> >> +static int virtio_link_supplier(struct device *dev)
> >> +{
> >> +       struct device *vdev = driver_find_device(
> >> +               &virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> >> +
> >> +       if (!vdev) {
> >> +               dev_notice_once(
> >> +                       dev,
> >> +                       "Deferring probe after not finding a bound scmi-virtio device\n");
> >> +               return -EPROBE_DEFER;
> >> +       }
> >> +
> >> +       /* Add device link for remove order and sysfs link. */
> >> +       if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> >> +               put_device(vdev);
> >> +               dev_err(dev, "Adding link to supplier virtio device failed\n");
> >> +               return -ECANCELED;
> >> +       }
> >> +
> >> +       put_device(vdev);
> >> +       return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> >> +}
> >> +
> >> +static bool virtio_chan_available(struct device *dev, int idx)
> >> +{
> >> +       struct virtio_device *vdev;
> >> +
> >> +       /* scmi-virtio doesn't support per-protocol channels */
> >> +       if (is_scmi_protocol_device(dev))
> >> +               return false;
> >> +
> >> +       vdev = scmi_get_transport_info(dev);
> >> +       if (!vdev)
> >> +               return false;
> >> +
> >> +       switch (idx) {
> >> +       case VIRTIO_SCMI_VQ_TX:
> >> +               return true;
> >> +       case VIRTIO_SCMI_VQ_RX:
> >> +               return scmi_vio_have_vq_rx(vdev);
> >> +       default:
> >> +               return false;
> >> +       }
> >> +}
> >> +
> >> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> >> +                            bool tx)
> >> +{
> >> +       unsigned long flags;
> >> +       struct virtio_device *vdev;
> >> +       struct scmi_vio_channel *vioch;
> >> +       int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> >> +       int max_msg;
> >> +       int i;
> >> +
> >> +       if (!virtio_chan_available(dev, index))
> >> +               return -ENODEV;
> >> +
> >> +       vdev = scmi_get_transport_info(dev);
> >> +       vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> >> +
> >> +       spin_lock_irqsave(&vioch->lock, flags);
> >> +       cinfo->transport_info = vioch;
> >> +       vioch->cinfo = cinfo;
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +       max_msg = virtio_get_max_msg(tx, cinfo);
> >> +
> >> +       for (i = 0; i < max_msg; i++) {
> >> +               struct scmi_vio_msg *msg;
> >> +
> >> +               msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> >> +               if (!msg)
> >> +                       return -ENOMEM;
> >> +
> >> +               if (tx) {
> >> +                       msg->request = devm_kzalloc(cinfo->dev,
> >> +                                                   VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +                                                   GFP_KERNEL);
> >> +                       if (!msg->request)
> >> +                               return -ENOMEM;
> >> +               }
> >> +
> >> +               msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +                                         GFP_KERNEL);
> >> +               if (!msg->input)
> >> +                       return -ENOMEM;
> >> +
> >> +               if (tx) {
> >> +                       spin_lock_irqsave(&vioch->lock, flags);
> >> +                       list_add_tail(&msg->list, &vioch->free_list);
> >> +                       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +               } else {
> >> +                       scmi_vio_feed_vq_rx(vioch, msg);
> >> +               }
> >> +       }
> >> +
> >> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +       vioch->ready = true;
> >> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static int virtio_chan_free(int id, void *p, void *data)
> >> +{
> >> +       unsigned long flags;
> >> +       struct scmi_chan_info *cinfo = p;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +       vioch->ready = false;
> >> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +       scmi_free_channel(cinfo, data, id);
> >> +       return 0;
> >> +}
> >> +
> >> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> >> +                              struct scmi_xfer *xfer)
> >> +{
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +       struct scatterlist sg_out;
> >> +       struct scatterlist sg_in;
> >> +       struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> >> +       unsigned long flags;
> >> +       int rc;
> >> +       struct scmi_vio_msg *msg;
> >> +
> >> +       /*
> >> +        * TODO: For now, we don't support polling. But it should not be
> >> +        * difficult to add support.
> >> +        */
> >> +       if (xfer->hdr.poll_completion)
> >> +               return -EINVAL;
> >> +
> >> +       spin_lock_irqsave(&vioch->lock, flags);
> >> +
> >> +       if (list_empty(&vioch->free_list)) {
> >> +               spin_unlock_irqrestore(&vioch->lock, flags);
> >> +               return -EBUSY;
> >> +       }
> >> +
> >> +       msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> >> +       list_del(&msg->list);
> >> +
> >> +       msg_tx_prepare(msg->request, xfer);
> >> +
> >> +       sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> >> +       sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> >> +
> >> +       rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> >> +       if (rc) {
> >> +               list_add(&msg->list, &vioch->free_list);
> >> +               dev_err_once(vioch->cinfo->dev,
> >> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
> >> +                            rc);
> >> +       } else {
> >> +               virtqueue_kick(vioch->vqueue);
> >> +       }
> >> +
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +       return rc;
> >> +}
> >> +
> >> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> >> +                                 struct scmi_xfer *xfer, void *msg_handle)
> >> +{
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       msg_fetch_response(msg->input, msg->rx_len, xfer);
> >> +}
> >> +
> >> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> >> +                                     size_t max_len, struct scmi_xfer *xfer,
> >> +                                     void *msg_handle)
> >> +{
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> >> +}
> >> +
> >> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> >> +{
> >> +}
> >> +
> >> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> >> +                           struct scmi_xfer *xfer)
> >> +{
> >> +       return false;
> >> +}
> >> +
> >> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> >> +{
> >> +       unsigned long flags;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       if (vioch->is_rx) {
> >> +               scmi_vio_feed_vq_rx(vioch, msg);
> >> +       } else {
> >> +               spin_lock_irqsave(&vioch->lock, flags);
> >> +               list_add(&msg->list, &vioch->free_list);
> >> +               spin_unlock_irqrestore(&vioch->lock, flags);
> >> +       }
> >> +}
> >> +
> >> +static const struct scmi_transport_ops scmi_virtio_ops = {
> >> +       .link_supplier = virtio_link_supplier,
> >> +       .chan_available = virtio_chan_available,
> >> +       .chan_setup = virtio_chan_setup,
> >> +       .chan_free = virtio_chan_free,
> >> +       .get_max_msg = virtio_get_max_msg,
> >> +       .send_message = virtio_send_message,
> >> +       .fetch_response = virtio_fetch_response,
> >> +       .fetch_notification = virtio_fetch_notification,
> >> +       .clear_channel = dummy_clear_channel,
> >> +       .poll_done = dummy_poll_done,
> >> +       .drop_message = virtio_drop_message,
> >> +};
> >> +
> >> +static int scmi_vio_probe(struct virtio_device *vdev)
> >> +{
> >> +       struct device *dev = &vdev->dev;
> >> +       struct scmi_vio_channel *channels;
> >> +       bool have_vq_rx;
> >> +       int vq_cnt;
> >> +       int i;
> >> +       int ret;
> >> +       struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> >> +
> >> +       have_vq_rx = scmi_vio_have_vq_rx(vdev);
> >> +       vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> >> +
> >> +       channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> >> +       if (!channels)
> >> +               return -ENOMEM;
> >> +
> >> +       if (have_vq_rx)
> >> +               channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> >> +
> >> +       ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> >> +                             scmi_vio_vqueue_names, NULL);
> >> +       if (ret) {
> >> +               dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> >> +               return ret;
> >> +       }
> >> +       dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> >> +
> >> +       for (i = 0; i < vq_cnt; i++) {
> >> +               spin_lock_init(&channels[i].lock);
> >> +               spin_lock_init(&channels[i].ready_lock);
> >> +               INIT_LIST_HEAD(&channels[i].free_list);
> >> +               channels[i].vqueue = vqs[i];
> >> +       }
> >> +
> >> +       vdev->priv = channels;
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static void scmi_vio_remove(struct virtio_device *vdev)
> >> +{
> >> +       vdev->config->reset(vdev);
> >> +       vdev->config->del_vqs(vdev);
> >> +}
> >> +
> >> +static unsigned int features[] = {
> >> +       VIRTIO_SCMI_F_P2A_CHANNELS,
> >> +};
> >> +
> >> +static const struct virtio_device_id id_table[] = {
> >> +       { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> >> +       { 0 }
> >> +};
> >> +
> >> +static struct virtio_driver virtio_scmi_driver = {
> >> +       .driver.name = "scmi-virtio",
> >> +       .driver.owner = THIS_MODULE,
> >> +       .feature_table = features,
> >> +       .feature_table_size = ARRAY_SIZE(features),
> >> +       .id_table = id_table,
> >> +       .probe = scmi_vio_probe,
> >> +       .remove = scmi_vio_remove,
> >> +};
> >> +
> >> +static int __init virtio_scmi_init(void)
> >> +{
> >> +       return register_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +static void __exit virtio_scmi_exit(void)
> >> +{
> >> +       unregister_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +const struct scmi_desc scmi_virtio_desc = {
> >> +       .init = virtio_scmi_init,
> >> +       .exit = virtio_scmi_exit,
> >> +       .ops = &scmi_virtio_ops,
> >> +       .max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> >> +       .max_msg = 0, /* overridden by virtio_get_max_msg() */
> >> +       .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> >> +};
> >> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> >> index f0c35ce8628c..c146fe30e589 100644
> >> --- a/include/uapi/linux/virtio_ids.h
> >> +++ b/include/uapi/linux/virtio_ids.h
> >> @@ -56,5 +56,6 @@
> >>  #define VIRTIO_ID_PMEM                 27 /* virtio pmem */
> >>  #define VIRTIO_ID_BT                   28 /* virtio bluetooth */
> >>  #define VIRTIO_ID_MAC80211_HWSIM       29 /* virtio mac80211-hwsim */
> >> +#define VIRTIO_ID_SCMI                 32 /* virtio SCMI */
> >>
> >>  #endif /* _LINUX_VIRTIO_IDS_H */
> >> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> >> new file mode 100644
> >> index 000000000000..732b01504c35
> >> --- /dev/null
> >> +++ b/include/uapi/linux/virtio_scmi.h
> >> @@ -0,0 +1,25 @@
> >> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> >> +/*
> >> + * Copyright (C) 2020 OpenSynergy GmbH
> >> + */
> >> +
> >> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> >> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> >> +
> >> +#include <linux/virtio_types.h>
> >> +
> >> +/* Feature bits */
> >> +
> >> +/* Device implements some SCMI notifications, or delayed responses. */
> >> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> >> +
> >> +/* Device implements any SCMI statistics shared memory region */
> >> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> >> +
> >> +/* Virtqueues */
> >> +
> >> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> >> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> >> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> >> +
> >> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> >> --
> >> 2.25.1
> >>
> >>
> > 
> 
>

Vincent Guittot June 2, 2021, 8:34 a.m. UTC | #6

On Wed, 2 Jun 2021 at 10:25, Peter Hilber <[e-mail]> wrote:
>
> On 01.06.21 16:53, Vincent Guittot wrote:
> > On Tue, 11 May 2021 at 02:28, Peter Hilber <[e-mail]> wrote:
> >>
> >> From: Igor Skalkin <[e-mail]>
> >>
> >> This transport enables accessing an SCMI platform as a virtio device.
> >>
> >> Implement an SCMI virtio driver according to the virtio SCMI device spec
> >> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
> >>
> >> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> >> at most one Rx channel (virtio eventq, P2A channel).
> >>
> >> The following feature bit defined in [1] is not implemented:
> >> VIRTIO_SCMI_F_SHARED_MEMORY.
> >>
> >> After the preparatory patches, this implements the virtio transport as
> >> paraphrased:
> >>
> >> Only support a single arm-scmi device (which is consistent with the SCMI
> >> spec). scmi-virtio init is called from arm-scmi module init. During the
> >> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> >> arm-scmi probing if no scmi-virtio device is bound yet.
> >>
> >> For simplicity, restrict the number of messages which can be pending
> >> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> >> are negotiated with the virtio device.)
> >>
> >> As soon as Rx channel message buffers are allocated or have been read
> >> out by the arm-scmi driver, feed them to the virtio device.
> >>
> >> Since some virtio devices may not have the short response time exhibited
> >> by SCMI platforms using other transports, set a generous response
> >> timeout.
> >>
> >> Limitations:
> >>
> >> - Polling is not supported.
> >>
> >> - The timeout for delayed responses has not been adjusted.
> >>
> >> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> >> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
> >>
> >> Signed-off-by: Igor Skalkin <[e-mail]>
> >> [ Peter: Adapted patch for submission to upstream. ]
> >> Co-developed-by: Peter Hilber <[e-mail]>
> >> Signed-off-by: Peter Hilber <[e-mail]>
> >> ---
> >>  MAINTAINERS                        |   1 +
> >>  drivers/firmware/Kconfig           |  12 +
> >>  drivers/firmware/arm_scmi/Makefile |   1 +
> >>  drivers/firmware/arm_scmi/common.h |   3 +
> >>  drivers/firmware/arm_scmi/driver.c |   3 +
> >>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
> >>  include/uapi/linux/virtio_ids.h    |   1 +
> >>  include/uapi/linux/virtio_scmi.h   |  25 ++
> >>  8 files changed, 569 insertions(+)
> >>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
> >>  create mode 100644 include/uapi/linux/virtio_scmi.h
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index bd7aff0c120f..449c336872f3 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -17705,6 +17705,7 @@ F:      drivers/regulator/scmi-regulator.c
> >>  F:     drivers/reset/reset-scmi.c
> >>  F:     include/linux/sc[mp]i_protocol.h
> >>  F:     include/trace/events/scmi.h
> >> +F:     include/uapi/linux/virtio_scmi.h
> >>
> >>  SYSTEM RESET/SHUTDOWN DRIVERS
> >>  M:     Sebastian Reichel <[e-mail]>
> >> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> >> index e8377b12e4d0..7e9eafdd9b63 100644
> >> --- a/drivers/firmware/Kconfig
> >> +++ b/drivers/firmware/Kconfig
> >> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
> >>           This declares whether a message passing based transport for SCMI is
> >>           available.
> >>
> >> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
> >> +# this config doesn't show up when SCMI wouldn't be available.
> >> +config VIRTIO_SCMI
> >> +       bool "Virtio transport for SCMI"
> >> +       select ARM_SCMI_HAVE_MSG
> >> +       depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
> >> +       help
> >> +         This enables the virtio based transport for SCMI.
> >> +
> >> +         If you want to use the ARM SCMI protocol between the virtio guest and
> >> +         a host providing a virtio SCMI device, answer Y.
> >> +
> >>  config ARM_SCMI_POWER_DOMAIN
> >>         tristate "SCMI power domain driver"
> >>         depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
> >> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> >> index f6b4acb8abdb..db1787606fb2 100644
> >> --- a/drivers/firmware/arm_scmi/Makefile
> >> +++ b/drivers/firmware/arm_scmi/Makefile
> >> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
> >>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
> >>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
> >>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
> >> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
> >>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
> >>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
> >>                     $(scmi-transport-y)
> >> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> >> index 4cb6571c7aaf..bada06cfd33d 100644
> >> --- a/drivers/firmware/arm_scmi/common.h
> >> +++ b/drivers/firmware/arm_scmi/common.h
> >> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
> >>  #ifdef CONFIG_HAVE_ARM_SMCCC
> >>  extern const struct scmi_desc scmi_smc_desc;
> >>  #endif
> >> +#ifdef CONFIG_VIRTIO_SCMI
> >> +extern const struct scmi_desc scmi_virtio_desc;
> >> +#endif
> >>
> >>  int scmi_set_transport_info(struct device *dev, void *transport_info);
> >>  void *scmi_get_transport_info(struct device *dev);
> >> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> >> index e04e7c8e6928..a31187385470 100644
> >> --- a/drivers/firmware/arm_scmi/driver.c
> >> +++ b/drivers/firmware/arm_scmi/driver.c
> >> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
> >>  #endif
> >>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
> >>         { .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> >> +#endif
> >> +#ifdef CONFIG_VIRTIO_SCMI
> >> +       { .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
> >>  #endif
> >>         { /* Sentinel */ },
> >>  };
> >> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> >> new file mode 100644
> >> index 000000000000..20972adf6dc7
> >> --- /dev/null
> >> +++ b/drivers/firmware/arm_scmi/virtio.c
> >> @@ -0,0 +1,523 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + * Virtio Transport driver for Arm System Control and Management Interface
> >> + * (SCMI).
> >> + *
> >> + * Copyright (C) 2020 OpenSynergy.
> >> + */
> >> +
> >> +/**
> >> + * DOC: Theory of Operation
> >> + *
> >> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
> >> + *
> >> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
> >> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
> >> + * virtqueue. Access to each virtqueue is protected by spinlocks.
> >> + */
> >> +
> >> +#include <linux/errno.h>
> >> +#include <linux/of.h>
> >> +#include <linux/of_platform.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/module.h>
> >> +#include <linux/slab.h>
> >> +#include <linux/virtio.h>
> >> +#include <linux/virtio_config.h>
> >> +#include <uapi/linux/virtio_ids.h>
> >> +#include <uapi/linux/virtio_scmi.h>
> >> +
> >> +#include "common.h"
> >> +
> >> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
> >> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
> >> +       (VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
> >> +#define DESCRIPTORS_PER_TX_MSG 2
> >> +
> >> +/**
> >> + * struct scmi_vio_channel - Transport channel information
> >> + *
> >> + * @lock: Protects access to all members except ready.
> >> + * @ready_lock: Protects access to ready. If required, it must be taken before
> >> + *              lock.
> >> + * @vqueue: Associated virtqueue
> >> + * @cinfo: SCMI Tx or Rx channel
> >> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> >> + * @is_rx: Whether channel is an Rx channel
> >> + * @ready: Whether transport user is ready to hear about channel
> >> + */
> >> +struct scmi_vio_channel {
> >> +       spinlock_t lock;
> >> +       spinlock_t ready_lock;
> >> +       struct virtqueue *vqueue;
> >> +       struct scmi_chan_info *cinfo;
> >> +       struct list_head free_list;
> >> +       u8 is_rx;
> >> +       u8 ready;
> >> +};
> >> +
> >> +/**
> >> + * struct scmi_vio_msg - Transport PDU information
> >> + *
> >> + * @request: SDU used for commands
> >> + * @input: SDU used for (delayed) responses and notifications
> >> + * @list: List which scmi_vio_msg may be part of
> >> + * @rx_len: Input SDU size in bytes, once input has been received
> >> + */
> >> +struct scmi_vio_msg {
> >> +       struct scmi_msg_payld *request;
> >> +       struct scmi_msg_payld *input;
> >> +       struct list_head list;
> >> +       unsigned int rx_len;
> >> +};
> >> +
> >> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> >> +{
> >> +       return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> >> +}
> >> +
> >> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> >> +                              struct scmi_vio_msg *msg)
> >> +{
> >> +       struct scatterlist sg_in;
> >> +       int rc;
> >> +       unsigned long flags;
> >> +
> >> +       sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
> >> +
> >> +       spin_lock_irqsave(&vioch->lock, flags);
> >> +
> >> +       rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
> >> +       if (rc)
> >> +               dev_err_once(vioch->cinfo->dev,
> >> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
> >> +                            rc);
> >> +       else
> >> +               virtqueue_kick(vioch->vqueue);
> >> +
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +       return rc;
> >> +}
> >> +
> >> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> >> +{
> >> +       unsigned long ready_flags;
> >> +       unsigned long flags;
> >> +       unsigned int length;
> >> +       struct scmi_vio_channel *vioch;
> >> +       struct scmi_vio_msg *msg;
> >> +       bool cb_enabled = true;
> >> +
> >> +       if (WARN_ON_ONCE(!vqueue->vdev->priv))
> >> +               return;
> >> +       vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
> >> +
> >> +       for (;;) {
> >> +               spin_lock_irqsave(&vioch->ready_lock, ready_flags);
> >> +
> >> +               if (!vioch->ready) {
> >> +                       if (!cb_enabled)
> >> +                               (void)virtqueue_enable_cb(vqueue);
> >> +                       goto unlock_ready_out;
> >> +               }
> >> +
> >> +               spin_lock_irqsave(&vioch->lock, flags);
> >> +               if (cb_enabled) {
> >> +                       virtqueue_disable_cb(vqueue);
> >> +                       cb_enabled = false;
> >> +               }
> >> +               msg = virtqueue_get_buf(vqueue, &length);
> >> +               if (!msg) {
> >> +                       if (virtqueue_enable_cb(vqueue))
> >> +                               goto unlock_out;
> >> +                       else
> >> +                               cb_enabled = true;
> >> +               }
> >> +               spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +               if (msg) {
> >> +                       msg->rx_len = length;
> >> +
> >> +                       /*
> >> +                        * Hold the ready_lock during the callback to avoid
> >> +                        * races when the arm-scmi driver is unbinding while
> >> +                        * the virtio device is not quiesced yet.
> >> +                        */
> >> +                       scmi_rx_callback(vioch->cinfo,
> >> +                                        msg_read_header(msg->input), msg);
> >> +               }
> >> +               spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> >> +       }
> >> +
> >> +unlock_out:
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +unlock_ready_out:
> >> +       spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> >> +}
> >> +
> >> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
> >> +
> >> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
> >> +       scmi_vio_complete_cb,
> >> +       scmi_vio_complete_cb
> >> +};
> >> +
> >> +static unsigned int virtio_get_max_msg(bool tx,
> >> +                                      struct scmi_chan_info *base_cinfo)
> >> +{
> >> +       struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> >> +       unsigned int ret;
> >> +
> >> +       ret = virtqueue_get_vring_size(vioch->vqueue);
> >> +
> >> +       /* Tx messages need multiple descriptors. */()
> >> +       if (tx)
> >> +               ret /= DESCRIPTORS_PER_TX_MSG;
> >> +
> >> +       if (ret > MSG_TOKEN_MAX) {
> >
> > __scmi_xfer_info_init() returns error for info->max_msg >=
> > MSG_TOKEN_MAX so it should be (ret >= MSG_TOKEN_MAX
> >
>
> I think it would be better to use the > comparison in
> __scmi_xfer_info_init(), too. That should work in my understanding. I

yes should work as well

> think that change was originally in my branch, but I lost it somehow.
>
> >
> >> +               dev_info_once(
> >> +                       base_cinfo->dev,
> >> +                       "Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> >> +                       MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> >> +               ret = MSG_TOKEN_MAX;
> >
> > should be ret = MSG_TOKEN_MAX-1;
> >
> >> +       }
> >> +
> >> +       return ret;
> >> +}
> >> +
> >> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> >> +{
> >> +       return 1;
> >> +}
> >> +
> >> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> >> +
> >> +static int virtio_link_supplier(struct device *dev)
> >> +{
> >> +       struct device *vdev = driver_find_device(
> >> +               &virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> >> +
> >> +       if (!vdev) {
> >> +               dev_notice_once(
> >> +                       dev,
> >> +                       "Deferring probe after not finding a bound scmi-virtio device\n");
> >> +               return -EPROBE_DEFER;
> >> +       }
> >> +
> >> +       /* Add device link for remove order and sysfs link. */
> >> +       if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> >> +               put_device(vdev);
> >> +               dev_err(dev, "Adding link to supplier virtio device failed\n");
> >> +               return -ECANCELED;
> >> +       }
> >> +
> >> +       put_device(vdev);
> >> +       return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> >> +}
> >> +
> >> +static bool virtio_chan_available(struct device *dev, int idx)
> >> +{
> >> +       struct virtio_device *vdev;
> >> +
> >> +       /* scmi-virtio doesn't support per-protocol channels */
> >> +       if (is_scmi_protocol_device(dev))
> >> +               return false;
> >> +
> >> +       vdev = scmi_get_transport_info(dev);
> >> +       if (!vdev)
> >> +               return false;
> >> +
> >> +       switch (idx) {
> >> +       case VIRTIO_SCMI_VQ_TX:
> >> +               return true;
> >> +       case VIRTIO_SCMI_VQ_RX:
> >> +               return scmi_vio_have_vq_rx(vdev);
> >> +       default:
> >> +               return false;
> >> +       }
> >> +}
> >> +
> >> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> >> +                            bool tx)
> >> +{
> >> +       unsigned long flags;
> >> +       struct virtio_device *vdev;
> >> +       struct scmi_vio_channel *vioch;
> >> +       int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> >> +       int max_msg;
> >> +       int i;
> >> +
> >> +       if (!virtio_chan_available(dev, index))
> >> +               return -ENODEV;
> >> +
> >> +       vdev = scmi_get_transport_info(dev);
> >> +       vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> >> +
> >> +       spin_lock_irqsave(&vioch->lock, flags);
> >> +       cinfo->transport_info = vioch;
> >> +       vioch->cinfo = cinfo;
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +       max_msg = virtio_get_max_msg(tx, cinfo);
> >> +
> >> +       for (i = 0; i < max_msg; i++) {
> >> +               struct scmi_vio_msg *msg;
> >> +
> >> +               msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> >> +               if (!msg)
> >> +                       return -ENOMEM;
> >> +
> >> +               if (tx) {
> >> +                       msg->request = devm_kzalloc(cinfo->dev,
> >> +                                                   VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +                                                   GFP_KERNEL);
> >> +                       if (!msg->request)
> >> +                               return -ENOMEM;
> >> +               }
> >> +
> >> +               msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +                                         GFP_KERNEL);
> >> +               if (!msg->input)
> >> +                       return -ENOMEM;
> >> +
> >> +               if (tx) {
> >> +                       spin_lock_irqsave(&vioch->lock, flags);
> >> +                       list_add_tail(&msg->list, &vioch->free_list);
> >> +                       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +               } else {
> >> +                       scmi_vio_feed_vq_rx(vioch, msg);
> >> +               }
> >> +       }
> >> +
> >> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +       vioch->ready = true;
> >> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static int virtio_chan_free(int id, void *p, void *data)
> >> +{
> >> +       unsigned long flags;
> >> +       struct scmi_chan_info *cinfo = p;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +       vioch->ready = false;
> >> +       spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +       scmi_free_channel(cinfo, data, id);
> >> +       return 0;
> >> +}
> >> +
> >> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> >> +                              struct scmi_xfer *xfer)
> >> +{
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +       struct scatterlist sg_out;
> >> +       struct scatterlist sg_in;
> >> +       struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> >> +       unsigned long flags;
> >> +       int rc;
> >> +       struct scmi_vio_msg *msg;
> >> +
> >> +       /*
> >> +        * TODO: For now, we don't support polling. But it should not be
> >> +        * difficult to add support.
> >> +        */
> >> +       if (xfer->hdr.poll_completion)
> >> +               return -EINVAL;
> >> +
> >> +       spin_lock_irqsave(&vioch->lock, flags);
> >> +
> >> +       if (list_empty(&vioch->free_list)) {
> >> +               spin_unlock_irqrestore(&vioch->lock, flags);
> >> +               return -EBUSY;
> >> +       }
> >> +
> >> +       msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> >> +       list_del(&msg->list);
> >> +
> >> +       msg_tx_prepare(msg->request, xfer);
> >> +
> >> +       sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> >> +       sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> >> +
> >> +       rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> >> +       if (rc) {
> >> +               list_add(&msg->list, &vioch->free_list);
> >> +               dev_err_once(vioch->cinfo->dev,
> >> +                            "%s() failed to add to virtqueue (%d)\n", __func__,
> >> +                            rc);
> >> +       } else {
> >> +               virtqueue_kick(vioch->vqueue);
> >> +       }
> >> +
> >> +       spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +       return rc;
> >> +}
> >> +
> >> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> >> +                                 struct scmi_xfer *xfer, void *msg_handle)
> >> +{
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       msg_fetch_response(msg->input, msg->rx_len, xfer);
> >> +}
> >> +
> >> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> >> +                                     size_t max_len, struct scmi_xfer *xfer,
> >> +                                     void *msg_handle)
> >> +{
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> >> +}
> >> +
> >> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> >> +{
> >> +}
> >> +
> >> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> >> +                           struct scmi_xfer *xfer)
> >> +{
> >> +       return false;
> >> +}
> >> +
> >> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> >> +{
> >> +       unsigned long flags;
> >> +       struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +       struct scmi_vio_msg *msg = msg_handle;
> >> +
> >> +       if (!msg) {
> >> +               dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +                            "Ignoring %s() call with NULL msg_handle\n",
> >> +                            __func__);
> >> +               return;
> >> +       }
> >> +
> >> +       if (vioch->is_rx) {
> >> +               scmi_vio_feed_vq_rx(vioch, msg);
> >> +       } else {
> >> +               spin_lock_irqsave(&vioch->lock, flags);
> >> +               list_add(&msg->list, &vioch->free_list);
> >> +               spin_unlock_irqrestore(&vioch->lock, flags);
> >> +       }
> >> +}
> >> +
> >> +static const struct scmi_transport_ops scmi_virtio_ops = {
> >> +       .link_supplier = virtio_link_supplier,
> >> +       .chan_available = virtio_chan_available,
> >> +       .chan_setup = virtio_chan_setup,
> >> +       .chan_free = virtio_chan_free,
> >> +       .get_max_msg = virtio_get_max_msg,
> >> +       .send_message = virtio_send_message,
> >> +       .fetch_response = virtio_fetch_response,
> >> +       .fetch_notification = virtio_fetch_notification,
> >> +       .clear_channel = dummy_clear_channel,
> >> +       .poll_done = dummy_poll_done,
> >> +       .drop_message = virtio_drop_message,
> >> +};
> >> +
> >> +static int scmi_vio_probe(struct virtio_device *vdev)
> >> +{
> >> +       struct device *dev = &vdev->dev;
> >> +       struct scmi_vio_channel *channels;
> >> +       bool have_vq_rx;
> >> +       int vq_cnt;
> >> +       int i;
> >> +       int ret;
> >> +       struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> >> +
> >> +       have_vq_rx = scmi_vio_have_vq_rx(vdev);
> >> +       vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> >> +
> >> +       channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> >> +       if (!channels)
> >> +               return -ENOMEM;
> >> +
> >> +       if (have_vq_rx)
> >> +               channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> >> +
> >> +       ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> >> +                             scmi_vio_vqueue_names, NULL);
> >> +       if (ret) {
> >> +               dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> >> +               return ret;
> >> +       }
> >> +       dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> >> +
> >> +       for (i = 0; i < vq_cnt; i++) {
> >> +               spin_lock_init(&channels[i].lock);
> >> +               spin_lock_init(&channels[i].ready_lock);
> >> +               INIT_LIST_HEAD(&channels[i].free_list);
> >> +               channels[i].vqueue = vqs[i];
> >> +       }
> >> +
> >> +       vdev->priv = channels;
> >> +
> >> +       return 0;
> >> +}
> >> +
> >> +static void scmi_vio_remove(struct virtio_device *vdev)
> >> +{
> >> +       vdev->config->reset(vdev);
> >> +       vdev->config->del_vqs(vdev);
> >> +}
> >> +
> >> +static unsigned int features[] = {
> >> +       VIRTIO_SCMI_F_P2A_CHANNELS,
> >> +};
> >> +
> >> +static const struct virtio_device_id id_table[] = {
> >> +       { VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> >> +       { 0 }
> >> +};
> >> +
> >> +static struct virtio_driver virtio_scmi_driver = {
> >> +       .driver.name = "scmi-virtio",
> >> +       .driver.owner = THIS_MODULE,
> >> +       .feature_table = features,
> >> +       .feature_table_size = ARRAY_SIZE(features),
> >> +       .id_table = id_table,
> >> +       .probe = scmi_vio_probe,
> >> +       .remove = scmi_vio_remove,
> >> +};
> >> +
> >> +static int __init virtio_scmi_init(void)
> >> +{
> >> +       return register_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +static void __exit virtio_scmi_exit(void)
> >> +{
> >> +       unregister_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +const struct scmi_desc scmi_virtio_desc = {
> >> +       .init = virtio_scmi_init,
> >> +       .exit = virtio_scmi_exit,
> >> +       .ops = &scmi_virtio_ops,
> >> +       .max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> >> +       .max_msg = 0, /* overridden by virtio_get_max_msg() */
> >> +       .max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> >> +};
> >> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> >> index f0c35ce8628c..c146fe30e589 100644
> >> --- a/include/uapi/linux/virtio_ids.h
> >> +++ b/include/uapi/linux/virtio_ids.h
> >> @@ -56,5 +56,6 @@
> >>  #define VIRTIO_ID_PMEM                 27 /* virtio pmem */
> >>  #define VIRTIO_ID_BT                   28 /* virtio bluetooth */
> >>  #define VIRTIO_ID_MAC80211_HWSIM       29 /* virtio mac80211-hwsim */
> >> +#define VIRTIO_ID_SCMI                 32 /* virtio SCMI */
> >>
> >>  #endif /* _LINUX_VIRTIO_IDS_H */
> >> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> >> new file mode 100644
> >> index 000000000000..732b01504c35
> >> --- /dev/null
> >> +++ b/include/uapi/linux/virtio_scmi.h
> >> @@ -0,0 +1,25 @@
> >> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> >> +/*
> >> + * Copyright (C) 2020 OpenSynergy GmbH
> >> + */
> >> +
> >> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> >> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> >> +
> >> +#include <linux/virtio_types.h>
> >> +
> >> +/* Feature bits */
> >> +
> >> +/* Device implements some SCMI notifications, or delayed responses. */
> >> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> >> +
> >> +/* Device implements any SCMI statistics shared memory region */
> >> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> >> +
> >> +/* Virtqueues */
> >> +
> >> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> >> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> >> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> >> +
> >> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> >> --
> >> 2.25.1
> >>
> >>
> >
>
>

Peter Hilber June 4, 2021, 9:19 a.m. UTC | #7

On 26.05.21 16:40, Cristian Marussi wrote:
> Hi Peter,
> 
> as anticipated I'm adding some new SCMI core mechanisms that should help
> simplyfying virtio-scmi series.
> 
> Such core work is still in progress (and to be properly reviewed) and it
> is at:
> 
> https://lore.kernel.org/linux-arm-kernel/[e-mail]/
> 
> but in the meantime I have an initial but working (for me at least :D)
> rework of your V3 virtio-scmi series; rework is still in progress and to be
> cleaned up (nor I have addressed probing sequence or polling mode), and I am
> anyway holding it for now since Rob asked about DT txt-to-yaml conversion
> too, BUT if you can or want to have a look in the meantime, you can find the
> whole V4 transitional series rebased on top of my core changes with some
> changes on top at:
> 
> https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_virtio_trans_V4_rework/
> 
> where:
> 
>  - I dropped V3 patches 7,8,12
>  - the virtio changes I applied to make use of my core changes are all
>    embedded in the last patch (just for now):
>    
>  	[RFC] firmware: arm_scmi: make virtio-scmi use delegated xfers
> 
> Definitely not the final version, so you may want to just wait for a
> real V4, but just to give an idea of the direction I'm trying to follow
> if you want.
> 
> Thanks,
> Cristian
> 

Hi Cristian,

I had a look at the concepts in the linked branch. The following race
condition seems to not be addressed ATM:

- concurrent not delayed and delayed response (or inverted order)

The virtio device will send the not delayed and delayed response through
different virtqueues. Sending in a particular order will in my
understanding not entail that the receiver is able to restore this
order. I think the virtio transport cannot handle this race condition in
general without interpreting message headers (which it shouldn't).

Also, it might be documented that after a response timeout, do_xfer
should not be called on the xfer any more (since a belated response to
the timed out message might corrupt the new message).

Best regards,

Peter

> On Tue, May 11, 2021 at 02:20:39AM +0200, Peter Hilber wrote:
>> From: Igor Skalkin <[e-mail]>
>>
>> This transport enables accessing an SCMI platform as a virtio device.
>>
>> Implement an SCMI virtio driver according to the virtio SCMI device spec
>> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
>>
>> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
>> at most one Rx channel (virtio eventq, P2A channel).
>>
>> The following feature bit defined in [1] is not implemented:
>> VIRTIO_SCMI_F_SHARED_MEMORY.
>>
>> After the preparatory patches, this implements the virtio transport as
>> paraphrased:
>>
>> Only support a single arm-scmi device (which is consistent with the SCMI
>> spec). scmi-virtio init is called from arm-scmi module init. During the
>> arm-scmi probing, link to the first probed scmi-virtio device. Defer
>> arm-scmi probing if no scmi-virtio device is bound yet.
>>
>> For simplicity, restrict the number of messages which can be pending
>> simultaneously according to the virtqueue capacity. (The virtqueue sizes
>> are negotiated with the virtio device.)
>>
>> As soon as Rx channel message buffers are allocated or have been read
>> out by the arm-scmi driver, feed them to the virtio device.
>>
>> Since some virtio devices may not have the short response time exhibited
>> by SCMI platforms using other transports, set a generous response
>> timeout.
>>
>> Limitations:
>>
>> - Polling is not supported.
>>
>> - The timeout for delayed responses has not been adjusted.
>>
>> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
>> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
>>
>> Signed-off-by: Igor Skalkin <[e-mail]>
>> [ Peter: Adapted patch for submission to upstream. ]
>> Co-developed-by: Peter Hilber <[e-mail]>
>> Signed-off-by: Peter Hilber <[e-mail]>
>> ---
>>  MAINTAINERS                        |   1 +
>>  drivers/firmware/Kconfig           |  12 +
>>  drivers/firmware/arm_scmi/Makefile |   1 +
>>  drivers/firmware/arm_scmi/common.h |   3 +
>>  drivers/firmware/arm_scmi/driver.c |   3 +
>>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
>>  include/uapi/linux/virtio_ids.h    |   1 +
>>  include/uapi/linux/virtio_scmi.h   |  25 ++
>>  8 files changed, 569 insertions(+)
>>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
>>  create mode 100644 include/uapi/linux/virtio_scmi.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index bd7aff0c120f..449c336872f3 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -17705,6 +17705,7 @@ F:	drivers/regulator/scmi-regulator.c
>>  F:	drivers/reset/reset-scmi.c
>>  F:	include/linux/sc[mp]i_protocol.h
>>  F:	include/trace/events/scmi.h
>> +F:	include/uapi/linux/virtio_scmi.h
>>  
>>  SYSTEM RESET/SHUTDOWN DRIVERS
>>  M:	Sebastian Reichel <[e-mail]>
>> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
>> index e8377b12e4d0..7e9eafdd9b63 100644
>> --- a/drivers/firmware/Kconfig
>> +++ b/drivers/firmware/Kconfig
>> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
>>  	  This declares whether a message passing based transport for SCMI is
>>  	  available.
>>  
>> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
>> +# this config doesn't show up when SCMI wouldn't be available.
>> +config VIRTIO_SCMI
>> +	bool "Virtio transport for SCMI"
>> +	select ARM_SCMI_HAVE_MSG
>> +	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
>> +	help
>> +	  This enables the virtio based transport for SCMI.
>> +
>> +	  If you want to use the ARM SCMI protocol between the virtio guest and
>> +	  a host providing a virtio SCMI device, answer Y.
>> +
>>  config ARM_SCMI_POWER_DOMAIN
>>  	tristate "SCMI power domain driver"
>>  	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
>> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
>> index f6b4acb8abdb..db1787606fb2 100644
>> --- a/drivers/firmware/arm_scmi/Makefile
>> +++ b/drivers/firmware/arm_scmi/Makefile
>> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
>>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
>>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
>>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
>> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
>>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
>>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
>>  		    $(scmi-transport-y)
>> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
>> index 4cb6571c7aaf..bada06cfd33d 100644
>> --- a/drivers/firmware/arm_scmi/common.h
>> +++ b/drivers/firmware/arm_scmi/common.h
>> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
>>  #ifdef CONFIG_HAVE_ARM_SMCCC
>>  extern const struct scmi_desc scmi_smc_desc;
>>  #endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +extern const struct scmi_desc scmi_virtio_desc;
>> +#endif
>>  
>>  int scmi_set_transport_info(struct device *dev, void *transport_info);
>>  void *scmi_get_transport_info(struct device *dev);
>> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
>> index e04e7c8e6928..a31187385470 100644
>> --- a/drivers/firmware/arm_scmi/driver.c
>> +++ b/drivers/firmware/arm_scmi/driver.c
>> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
>>  #endif
>>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>>  	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
>> +#endif
>> +#ifdef CONFIG_VIRTIO_SCMI
>> +	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
>>  #endif
>>  	{ /* Sentinel */ },
>>  };
>> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
>> new file mode 100644
>> index 000000000000..20972adf6dc7
>> --- /dev/null
>> +++ b/drivers/firmware/arm_scmi/virtio.c
>> @@ -0,0 +1,523 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Virtio Transport driver for Arm System Control and Management Interface
>> + * (SCMI).
>> + *
>> + * Copyright (C) 2020 OpenSynergy.
>> + */
>> +
>> +/**
>> + * DOC: Theory of Operation
>> + *
>> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
>> + *
>> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
>> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
>> + * virtqueue. Access to each virtqueue is protected by spinlocks.
>> + */
>> +
>> +#include <linux/errno.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/module.h>
>> +#include <linux/slab.h>
>> +#include <linux/virtio.h>
>> +#include <linux/virtio_config.h>
>> +#include <uapi/linux/virtio_ids.h>
>> +#include <uapi/linux/virtio_scmi.h>
>> +
>> +#include "common.h"
>> +
>> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
>> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
>> +	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
>> +#define DESCRIPTORS_PER_TX_MSG 2
>> +
>> +/**
>> + * struct scmi_vio_channel - Transport channel information
>> + *
>> + * @lock: Protects access to all members except ready.
>> + * @ready_lock: Protects access to ready. If required, it must be taken before
>> + *              lock.
>> + * @vqueue: Associated virtqueue
>> + * @cinfo: SCMI Tx or Rx channel
>> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
>> + * @is_rx: Whether channel is an Rx channel
>> + * @ready: Whether transport user is ready to hear about channel
>> + */
>> +struct scmi_vio_channel {
>> +	spinlock_t lock;
>> +	spinlock_t ready_lock;
>> +	struct virtqueue *vqueue;
>> +	struct scmi_chan_info *cinfo;
>> +	struct list_head free_list;
>> +	u8 is_rx;
>> +	u8 ready;
>> +};
>> +
>> +/**
>> + * struct scmi_vio_msg - Transport PDU information
>> + *
>> + * @request: SDU used for commands
>> + * @input: SDU used for (delayed) responses and notifications
>> + * @list: List which scmi_vio_msg may be part of
>> + * @rx_len: Input SDU size in bytes, once input has been received
>> + */
>> +struct scmi_vio_msg {
>> +	struct scmi_msg_payld *request;
>> +	struct scmi_msg_payld *input;
>> +	struct list_head list;
>> +	unsigned int rx_len;
>> +};
>> +
>> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
>> +{
>> +	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
>> +}
>> +
>> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
>> +			       struct scmi_vio_msg *msg)
>> +{
>> +	struct scatterlist sg_in;
>> +	int rc;
>> +	unsigned long flags;
>> +
>> +	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
>> +	if (rc)
>> +		dev_err_once(vioch->cinfo->dev,
>> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
>> +			     rc);
>> +	else
>> +		virtqueue_kick(vioch->vqueue);
>> +
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	return rc;
>> +}
>> +
>> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
>> +{
>> +	unsigned long ready_flags;
>> +	unsigned long flags;
>> +	unsigned int length;
>> +	struct scmi_vio_channel *vioch;
>> +	struct scmi_vio_msg *msg;
>> +	bool cb_enabled = true;
>> +
>> +	if (WARN_ON_ONCE(!vqueue->vdev->priv))
>> +		return;
>> +	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
>> +
>> +	for (;;) {
>> +		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
>> +
>> +		if (!vioch->ready) {
>> +			if (!cb_enabled)
>> +				(void)virtqueue_enable_cb(vqueue);
>> +			goto unlock_ready_out;
>> +		}
>> +
>> +		spin_lock_irqsave(&vioch->lock, flags);
>> +		if (cb_enabled) {
>> +			virtqueue_disable_cb(vqueue);
>> +			cb_enabled = false;
>> +		}
>> +		msg = virtqueue_get_buf(vqueue, &length);
>> +		if (!msg) {
>> +			if (virtqueue_enable_cb(vqueue))
>> +				goto unlock_out;
>> +			else
>> +				cb_enabled = true;
>> +		}
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +		if (msg) {
>> +			msg->rx_len = length;
>> +
>> +			/*
>> +			 * Hold the ready_lock during the callback to avoid
>> +			 * races when the arm-scmi driver is unbinding while
>> +			 * the virtio device is not quiesced yet.
>> +			 */
>> +			scmi_rx_callback(vioch->cinfo,
>> +					 msg_read_header(msg->input), msg);
>> +		}
>> +		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +	}
>> +
>> +unlock_out:
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +unlock_ready_out:
>> +	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
>> +}
>> +
>> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
>> +
>> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
>> +	scmi_vio_complete_cb,
>> +	scmi_vio_complete_cb
>> +};
>> +
>> +static unsigned int virtio_get_max_msg(bool tx,
>> +				       struct scmi_chan_info *base_cinfo)
>> +{
>> +	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
>> +	unsigned int ret;
>> +
>> +	ret = virtqueue_get_vring_size(vioch->vqueue);
>> +
>> +	/* Tx messages need multiple descriptors. */
>> +	if (tx)
>> +		ret /= DESCRIPTORS_PER_TX_MSG;
>> +
>> +	if (ret > MSG_TOKEN_MAX) {
>> +		dev_info_once(
>> +			base_cinfo->dev,
>> +			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
>> +			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
>> +		ret = MSG_TOKEN_MAX;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
>> +{
>> +	return 1;
>> +}
>> +
>> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
>> +
>> +static int virtio_link_supplier(struct device *dev)
>> +{
>> +	struct device *vdev = driver_find_device(
>> +		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
>> +
>> +	if (!vdev) {
>> +		dev_notice_once(
>> +			dev,
>> +			"Deferring probe after not finding a bound scmi-virtio device\n");
>> +		return -EPROBE_DEFER;
>> +	}
>> +
>> +	/* Add device link for remove order and sysfs link. */
>> +	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
>> +		put_device(vdev);
>> +		dev_err(dev, "Adding link to supplier virtio device failed\n");
>> +		return -ECANCELED;
>> +	}
>> +
>> +	put_device(vdev);
>> +	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
>> +}
>> +
>> +static bool virtio_chan_available(struct device *dev, int idx)
>> +{
>> +	struct virtio_device *vdev;
>> +
>> +	/* scmi-virtio doesn't support per-protocol channels */
>> +	if (is_scmi_protocol_device(dev))
>> +		return false;
>> +
>> +	vdev = scmi_get_transport_info(dev);
>> +	if (!vdev)
>> +		return false;
>> +
>> +	switch (idx) {
>> +	case VIRTIO_SCMI_VQ_TX:
>> +		return true;
>> +	case VIRTIO_SCMI_VQ_RX:
>> +		return scmi_vio_have_vq_rx(vdev);
>> +	default:
>> +		return false;
>> +	}
>> +}
>> +
>> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>> +			     bool tx)
>> +{
>> +	unsigned long flags;
>> +	struct virtio_device *vdev;
>> +	struct scmi_vio_channel *vioch;
>> +	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
>> +	int max_msg;
>> +	int i;
>> +
>> +	if (!virtio_chan_available(dev, index))
>> +		return -ENODEV;
>> +
>> +	vdev = scmi_get_transport_info(dev);
>> +	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +	cinfo->transport_info = vioch;
>> +	vioch->cinfo = cinfo;
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	max_msg = virtio_get_max_msg(tx, cinfo);
>> +
>> +	for (i = 0; i < max_msg; i++) {
>> +		struct scmi_vio_msg *msg;
>> +
>> +		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
>> +		if (!msg)
>> +			return -ENOMEM;
>> +
>> +		if (tx) {
>> +			msg->request = devm_kzalloc(cinfo->dev,
>> +						    VIRTIO_SCMI_MAX_PDU_SIZE,
>> +						    GFP_KERNEL);
>> +			if (!msg->request)
>> +				return -ENOMEM;
>> +		}
>> +
>> +		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
>> +					  GFP_KERNEL);
>> +		if (!msg->input)
>> +			return -ENOMEM;
>> +
>> +		if (tx) {
>> +			spin_lock_irqsave(&vioch->lock, flags);
>> +			list_add_tail(&msg->list, &vioch->free_list);
>> +			spin_unlock_irqrestore(&vioch->lock, flags);
>> +		} else {
>> +			scmi_vio_feed_vq_rx(vioch, msg);
>> +		}
>> +	}
>> +
>> +	spin_lock_irqsave(&vioch->ready_lock, flags);
>> +	vioch->ready = true;
>> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +	return 0;
>> +}
>> +
>> +static int virtio_chan_free(int id, void *p, void *data)
>> +{
>> +	unsigned long flags;
>> +	struct scmi_chan_info *cinfo = p;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	spin_lock_irqsave(&vioch->ready_lock, flags);
>> +	vioch->ready = false;
>> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
>> +
>> +	scmi_free_channel(cinfo, data, id);
>> +	return 0;
>> +}
>> +
>> +static int virtio_send_message(struct scmi_chan_info *cinfo,
>> +			       struct scmi_xfer *xfer)
>> +{
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +	struct scatterlist sg_out;
>> +	struct scatterlist sg_in;
>> +	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
>> +	unsigned long flags;
>> +	int rc;
>> +	struct scmi_vio_msg *msg;
>> +
>> +	/*
>> +	 * TODO: For now, we don't support polling. But it should not be
>> +	 * difficult to add support.
>> +	 */
>> +	if (xfer->hdr.poll_completion)
>> +		return -EINVAL;
>> +
>> +	spin_lock_irqsave(&vioch->lock, flags);
>> +
>> +	if (list_empty(&vioch->free_list)) {
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +		return -EBUSY;
>> +	}
>> +
>> +	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
>> +	list_del(&msg->list);
>> +
>> +	msg_tx_prepare(msg->request, xfer);
>> +
>> +	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
>> +	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
>> +
>> +	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
>> +	if (rc) {
>> +		list_add(&msg->list, &vioch->free_list);
>> +		dev_err_once(vioch->cinfo->dev,
>> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
>> +			     rc);
>> +	} else {
>> +		virtqueue_kick(vioch->vqueue);
>> +	}
>> +
>> +	spin_unlock_irqrestore(&vioch->lock, flags);
>> +
>> +	return rc;
>> +}
>> +
>> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
>> +				  struct scmi_xfer *xfer, void *msg_handle)
>> +{
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	msg_fetch_response(msg->input, msg->rx_len, xfer);
>> +}
>> +
>> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
>> +				      size_t max_len, struct scmi_xfer *xfer,
>> +				      void *msg_handle)
>> +{
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
>> +}
>> +
>> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
>> +{
>> +}
>> +
>> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
>> +			    struct scmi_xfer *xfer)
>> +{
>> +	return false;
>> +}
>> +
>> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
>> +{
>> +	unsigned long flags;
>> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
>> +	struct scmi_vio_msg *msg = msg_handle;
>> +
>> +	if (!msg) {
>> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
>> +			     "Ignoring %s() call with NULL msg_handle\n",
>> +			     __func__);
>> +		return;
>> +	}
>> +
>> +	if (vioch->is_rx) {
>> +		scmi_vio_feed_vq_rx(vioch, msg);
>> +	} else {
>> +		spin_lock_irqsave(&vioch->lock, flags);
>> +		list_add(&msg->list, &vioch->free_list);
>> +		spin_unlock_irqrestore(&vioch->lock, flags);
>> +	}
>> +}
>> +
>> +static const struct scmi_transport_ops scmi_virtio_ops = {
>> +	.link_supplier = virtio_link_supplier,
>> +	.chan_available = virtio_chan_available,
>> +	.chan_setup = virtio_chan_setup,
>> +	.chan_free = virtio_chan_free,
>> +	.get_max_msg = virtio_get_max_msg,
>> +	.send_message = virtio_send_message,
>> +	.fetch_response = virtio_fetch_response,
>> +	.fetch_notification = virtio_fetch_notification,
>> +	.clear_channel = dummy_clear_channel,
>> +	.poll_done = dummy_poll_done,
>> +	.drop_message = virtio_drop_message,
>> +};
>> +
>> +static int scmi_vio_probe(struct virtio_device *vdev)
>> +{
>> +	struct device *dev = &vdev->dev;
>> +	struct scmi_vio_channel *channels;
>> +	bool have_vq_rx;
>> +	int vq_cnt;
>> +	int i;
>> +	int ret;
>> +	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
>> +
>> +	have_vq_rx = scmi_vio_have_vq_rx(vdev);
>> +	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
>> +
>> +	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
>> +	if (!channels)
>> +		return -ENOMEM;
>> +
>> +	if (have_vq_rx)
>> +		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
>> +
>> +	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
>> +			      scmi_vio_vqueue_names, NULL);
>> +	if (ret) {
>> +		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
>> +		return ret;
>> +	}
>> +	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
>> +
>> +	for (i = 0; i < vq_cnt; i++) {
>> +		spin_lock_init(&channels[i].lock);
>> +		spin_lock_init(&channels[i].ready_lock);
>> +		INIT_LIST_HEAD(&channels[i].free_list);
>> +		channels[i].vqueue = vqs[i];
>> +	}
>> +
>> +	vdev->priv = channels;
>> +
>> +	return 0;
>> +}
>> +
>> +static void scmi_vio_remove(struct virtio_device *vdev)
>> +{
>> +	vdev->config->reset(vdev);
>> +	vdev->config->del_vqs(vdev);
>> +}
>> +
>> +static unsigned int features[] = {
>> +	VIRTIO_SCMI_F_P2A_CHANNELS,
>> +};
>> +
>> +static const struct virtio_device_id id_table[] = {
>> +	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
>> +	{ 0 }
>> +};
>> +
>> +static struct virtio_driver virtio_scmi_driver = {
>> +	.driver.name = "scmi-virtio",
>> +	.driver.owner = THIS_MODULE,
>> +	.feature_table = features,
>> +	.feature_table_size = ARRAY_SIZE(features),
>> +	.id_table = id_table,
>> +	.probe = scmi_vio_probe,
>> +	.remove = scmi_vio_remove,
>> +};
>> +
>> +static int __init virtio_scmi_init(void)
>> +{
>> +	return register_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +static void __exit virtio_scmi_exit(void)
>> +{
>> +	unregister_virtio_driver(&virtio_scmi_driver);
>> +}
>> +
>> +const struct scmi_desc scmi_virtio_desc = {
>> +	.init = virtio_scmi_init,
>> +	.exit = virtio_scmi_exit,
>> +	.ops = &scmi_virtio_ops,
>> +	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
>> +	.max_msg = 0, /* overridden by virtio_get_max_msg() */
>> +	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
>> +};
>> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
>> index f0c35ce8628c..c146fe30e589 100644
>> --- a/include/uapi/linux/virtio_ids.h
>> +++ b/include/uapi/linux/virtio_ids.h
>> @@ -56,5 +56,6 @@
>>  #define VIRTIO_ID_PMEM			27 /* virtio pmem */
>>  #define VIRTIO_ID_BT			28 /* virtio bluetooth */
>>  #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
>> +#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
>>  
>>  #endif /* _LINUX_VIRTIO_IDS_H */
>> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
>> new file mode 100644
>> index 000000000000..732b01504c35
>> --- /dev/null
>> +++ b/include/uapi/linux/virtio_scmi.h
>> @@ -0,0 +1,25 @@
>> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
>> +/*
>> + * Copyright (C) 2020 OpenSynergy GmbH
>> + */
>> +
>> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
>> +#define _UAPI_LINUX_VIRTIO_SCMI_H
>> +
>> +#include <linux/virtio_types.h>
>> +
>> +/* Feature bits */
>> +
>> +/* Device implements some SCMI notifications, or delayed responses. */
>> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
>> +
>> +/* Device implements any SCMI statistics shared memory region */
>> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
>> +
>> +/* Virtqueues */
>> +
>> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
>> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
>> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
>> +
>> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
>> -- 
>> 2.25.1
>>
>>
>

Cristian Marussi June 4, 2021, 11:56 a.m. UTC | #8

Hi Peter,

first of all thanks a lot for having a look at this draft work.

On Fri, Jun 04, 2021 at 11:19:02AM +0200, Peter Hilber wrote:
> On 26.05.21 16:40, Cristian Marussi wrote:
> > Hi Peter,
> > 
> > as anticipated I'm adding some new SCMI core mechanisms that should help
> > simplyfying virtio-scmi series.
> > 
> > Such core work is still in progress (and to be properly reviewed) and it
> > is at:
> > 
> > https://lore.kernel.org/linux-arm-kernel/[e-mail]/
> > 
> > but in the meantime I have an initial but working (for me at least :D)
> > rework of your V3 virtio-scmi series; rework is still in progress and to be
> > cleaned up (nor I have addressed probing sequence or polling mode), and I am
> > anyway holding it for now since Rob asked about DT txt-to-yaml conversion
> > too, BUT if you can or want to have a look in the meantime, you can find the
> > whole V4 transitional series rebased on top of my core changes with some
> > changes on top at:
> > 
> > https://gitlab.arm.com/linux-arm/linux-cm/-/commits/scmi_virtio_trans_V4_rework/
> > 
> > where:
> > 
> >  - I dropped V3 patches 7,8,12
> >  - the virtio changes I applied to make use of my core changes are all
> >    embedded in the last patch (just for now):
> >    
> >  	[RFC] firmware: arm_scmi: make virtio-scmi use delegated xfers
> > 
> > Definitely not the final version, so you may want to just wait for a
> > real V4, but just to give an idea of the direction I'm trying to follow
> > if you want.
> > 
> > Thanks,
> > Cristian
> > 
> 
> Hi Cristian,
> 
> I had a look at the concepts in the linked branch. The following race
> condition seems to not be addressed ATM:
> 
> - concurrent not delayed and delayed response (or inverted order)
> 
> The virtio device will send the not delayed and delayed response through
> different virtqueues. Sending in a particular order will in my
> understanding not entail that the receiver is able to restore this
> order. I think the virtio transport cannot handle this race condition in
> general without interpreting message headers (which it shouldn't).

The only valid assumption in SCMI comms should be that the platform is
constrained to send a delayed_resposne ONLY after the corresponding
sync-response is sent, but you are indeed right that, even when the
platform obeys such constraint, with this specific transport it could
happen, even though as a limit condition, that such messages, being
delivered through different vqueues, could be processed indeed concurrently
or inverted, so we should take care somehow of this situation.

I agree that virtio transport should not peek inside the message headers
and interpret them, but the core can do it when virtio::complete_cb()
looks for matching xfers, so I could detect this out-of-order condition
(in the core...adding some state info) and take 2 alternative actions:

 1. identify and discard such (rare ?) out-of-order (least desirable
    solution I think)

 2. assume that an expected dresp received ahead of a resp implies
    the related resp was OK (missing/lost ?), so maybe warn, BUT proceeed
    processing normally the dresp while forcibly completing the waiters for
    the missing sync-resp (with any future late arrival for that missing
    sync-resp seq_num discarded by the core...assuming seqs are now uniques
    and monotonically increasing..more on this below). This would
    require also better serializiation to avoid the concurrent case.

This is just off the top of my head, I have not think it througly, I'll
investigate 2. and see if can be kept reasonably simple and include in
V4 properly.

> 
> Also, it might be documented that after a response timeout, do_xfer
> should not be called on the xfer any more (since a belated response to
> the timed out message might corrupt the new message).
> 

So this is an interesting point because it is something that sort of I
wanted to get feedbaclk about; indeed the new monotonic sequence
numbers are assigned when an xfer is get, so that, in fact, if core
protocols then reuse the same xfer in a loop to send multiple similar
requests there is still a possibility of a late response being associated
with a new message (having the same seq), even though presumably the first
timeout would lead to such set of commands-in-loop to be aborted.

I knew that (:D) and I had indeed some (non-posted) patches where the
monotonically increasing token/seq is instead assigned brand new for each
do_xfer instead than when get ... I reverted to the current solution because
it was a bit simpler and I was not sure if it was worth trying to protect
also from the above 'loop' scenario. I'll rethink about this.

Thanks for the feedback,
Cristian

> Best regards,
> 
> Peter
> 
> > On Tue, May 11, 2021 at 02:20:39AM +0200, Peter Hilber wrote:
> >> From: Igor Skalkin <[e-mail]>
> >>
> >> This transport enables accessing an SCMI platform as a virtio device.
> >>
> >> Implement an SCMI virtio driver according to the virtio SCMI device spec
> >> [1]. Virtio device id 32 has been reserved for the SCMI device [2].
> >>
> >> The virtio transport has one Tx channel (virtio cmdq, A2P channel) and
> >> at most one Rx channel (virtio eventq, P2A channel).
> >>
> >> The following feature bit defined in [1] is not implemented:
> >> VIRTIO_SCMI_F_SHARED_MEMORY.
> >>
> >> After the preparatory patches, this implements the virtio transport as
> >> paraphrased:
> >>
> >> Only support a single arm-scmi device (which is consistent with the SCMI
> >> spec). scmi-virtio init is called from arm-scmi module init. During the
> >> arm-scmi probing, link to the first probed scmi-virtio device. Defer
> >> arm-scmi probing if no scmi-virtio device is bound yet.
> >>
> >> For simplicity, restrict the number of messages which can be pending
> >> simultaneously according to the virtqueue capacity. (The virtqueue sizes
> >> are negotiated with the virtio device.)
> >>
> >> As soon as Rx channel message buffers are allocated or have been read
> >> out by the arm-scmi driver, feed them to the virtio device.
> >>
> >> Since some virtio devices may not have the short response time exhibited
> >> by SCMI platforms using other transports, set a generous response
> >> timeout.
> >>
> >> Limitations:
> >>
> >> - Polling is not supported.
> >>
> >> - The timeout for delayed responses has not been adjusted.
> >>
> >> [1] https://github.com/oasis-tcs/virtio-spec/blob/master/virtio-scmi.tex
> >> [2] https://www.oasis-open.org/committees/ballot.php?id=3496
> >>
> >> Signed-off-by: Igor Skalkin <[e-mail]>
> >> [ Peter: Adapted patch for submission to upstream. ]
> >> Co-developed-by: Peter Hilber <[e-mail]>
> >> Signed-off-by: Peter Hilber <[e-mail]>
> >> ---
> >>  MAINTAINERS                        |   1 +
> >>  drivers/firmware/Kconfig           |  12 +
> >>  drivers/firmware/arm_scmi/Makefile |   1 +
> >>  drivers/firmware/arm_scmi/common.h |   3 +
> >>  drivers/firmware/arm_scmi/driver.c |   3 +
> >>  drivers/firmware/arm_scmi/virtio.c | 523 +++++++++++++++++++++++++++++
> >>  include/uapi/linux/virtio_ids.h    |   1 +
> >>  include/uapi/linux/virtio_scmi.h   |  25 ++
> >>  8 files changed, 569 insertions(+)
> >>  create mode 100644 drivers/firmware/arm_scmi/virtio.c
> >>  create mode 100644 include/uapi/linux/virtio_scmi.h
> >>
> >> diff --git a/MAINTAINERS b/MAINTAINERS
> >> index bd7aff0c120f..449c336872f3 100644
> >> --- a/MAINTAINERS
> >> +++ b/MAINTAINERS
> >> @@ -17705,6 +17705,7 @@ F:	drivers/regulator/scmi-regulator.c
> >>  F:	drivers/reset/reset-scmi.c
> >>  F:	include/linux/sc[mp]i_protocol.h
> >>  F:	include/trace/events/scmi.h
> >> +F:	include/uapi/linux/virtio_scmi.h
> >>  
> >>  SYSTEM RESET/SHUTDOWN DRIVERS
> >>  M:	Sebastian Reichel <[e-mail]>
> >> diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
> >> index e8377b12e4d0..7e9eafdd9b63 100644
> >> --- a/drivers/firmware/Kconfig
> >> +++ b/drivers/firmware/Kconfig
> >> @@ -39,6 +39,18 @@ config ARM_SCMI_HAVE_MSG
> >>  	  This declares whether a message passing based transport for SCMI is
> >>  	  available.
> >>  
> >> +# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
> >> +# this config doesn't show up when SCMI wouldn't be available.
> >> +config VIRTIO_SCMI
> >> +	bool "Virtio transport for SCMI"
> >> +	select ARM_SCMI_HAVE_MSG
> >> +	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
> >> +	help
> >> +	  This enables the virtio based transport for SCMI.
> >> +
> >> +	  If you want to use the ARM SCMI protocol between the virtio guest and
> >> +	  a host providing a virtio SCMI device, answer Y.
> >> +
> >>  config ARM_SCMI_POWER_DOMAIN
> >>  	tristate "SCMI power domain driver"
> >>  	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
> >> diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
> >> index f6b4acb8abdb..db1787606fb2 100644
> >> --- a/drivers/firmware/arm_scmi/Makefile
> >> +++ b/drivers/firmware/arm_scmi/Makefile
> >> @@ -5,6 +5,7 @@ scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
> >>  scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
> >>  scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
> >>  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
> >> +scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
> >>  scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
> >>  scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
> >>  		    $(scmi-transport-y)
> >> diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
> >> index 4cb6571c7aaf..bada06cfd33d 100644
> >> --- a/drivers/firmware/arm_scmi/common.h
> >> +++ b/drivers/firmware/arm_scmi/common.h
> >> @@ -349,6 +349,9 @@ extern const struct scmi_desc scmi_mailbox_desc;
> >>  #ifdef CONFIG_HAVE_ARM_SMCCC
> >>  extern const struct scmi_desc scmi_smc_desc;
> >>  #endif
> >> +#ifdef CONFIG_VIRTIO_SCMI
> >> +extern const struct scmi_desc scmi_virtio_desc;
> >> +#endif
> >>  
> >>  int scmi_set_transport_info(struct device *dev, void *transport_info);
> >>  void *scmi_get_transport_info(struct device *dev);
> >> diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> >> index e04e7c8e6928..a31187385470 100644
> >> --- a/drivers/firmware/arm_scmi/driver.c
> >> +++ b/drivers/firmware/arm_scmi/driver.c
> >> @@ -1637,6 +1637,9 @@ static const struct of_device_id scmi_of_match[] = {
> >>  #endif
> >>  #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
> >>  	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
> >> +#endif
> >> +#ifdef CONFIG_VIRTIO_SCMI
> >> +	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
> >>  #endif
> >>  	{ /* Sentinel */ },
> >>  };
> >> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> >> new file mode 100644
> >> index 000000000000..20972adf6dc7
> >> --- /dev/null
> >> +++ b/drivers/firmware/arm_scmi/virtio.c
> >> @@ -0,0 +1,523 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +/*
> >> + * Virtio Transport driver for Arm System Control and Management Interface
> >> + * (SCMI).
> >> + *
> >> + * Copyright (C) 2020 OpenSynergy.
> >> + */
> >> +
> >> +/**
> >> + * DOC: Theory of Operation
> >> + *
> >> + * The scmi-virtio transport implements a driver for the virtio SCMI device.
> >> + *
> >> + * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
> >> + * channel (virtio eventq, P2A channel). Each channel is implemented through a
> >> + * virtqueue. Access to each virtqueue is protected by spinlocks.
> >> + */
> >> +
> >> +#include <linux/errno.h>
> >> +#include <linux/of.h>
> >> +#include <linux/of_platform.h>
> >> +#include <linux/platform_device.h>
> >> +#include <linux/module.h>
> >> +#include <linux/slab.h>
> >> +#include <linux/virtio.h>
> >> +#include <linux/virtio_config.h>
> >> +#include <uapi/linux/virtio_ids.h>
> >> +#include <uapi/linux/virtio_scmi.h>
> >> +
> >> +#include "common.h"
> >> +
> >> +#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
> >> +#define VIRTIO_SCMI_MAX_PDU_SIZE \
> >> +	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
> >> +#define DESCRIPTORS_PER_TX_MSG 2
> >> +
> >> +/**
> >> + * struct scmi_vio_channel - Transport channel information
> >> + *
> >> + * @lock: Protects access to all members except ready.
> >> + * @ready_lock: Protects access to ready. If required, it must be taken before
> >> + *              lock.
> >> + * @vqueue: Associated virtqueue
> >> + * @cinfo: SCMI Tx or Rx channel
> >> + * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> >> + * @is_rx: Whether channel is an Rx channel
> >> + * @ready: Whether transport user is ready to hear about channel
> >> + */
> >> +struct scmi_vio_channel {
> >> +	spinlock_t lock;
> >> +	spinlock_t ready_lock;
> >> +	struct virtqueue *vqueue;
> >> +	struct scmi_chan_info *cinfo;
> >> +	struct list_head free_list;
> >> +	u8 is_rx;
> >> +	u8 ready;
> >> +};
> >> +
> >> +/**
> >> + * struct scmi_vio_msg - Transport PDU information
> >> + *
> >> + * @request: SDU used for commands
> >> + * @input: SDU used for (delayed) responses and notifications
> >> + * @list: List which scmi_vio_msg may be part of
> >> + * @rx_len: Input SDU size in bytes, once input has been received
> >> + */
> >> +struct scmi_vio_msg {
> >> +	struct scmi_msg_payld *request;
> >> +	struct scmi_msg_payld *input;
> >> +	struct list_head list;
> >> +	unsigned int rx_len;
> >> +};
> >> +
> >> +static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> >> +{
> >> +	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> >> +}
> >> +
> >> +static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> >> +			       struct scmi_vio_msg *msg)
> >> +{
> >> +	struct scatterlist sg_in;
> >> +	int rc;
> >> +	unsigned long flags;
> >> +
> >> +	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
> >> +
> >> +	spin_lock_irqsave(&vioch->lock, flags);
> >> +
> >> +	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
> >> +	if (rc)
> >> +		dev_err_once(vioch->cinfo->dev,
> >> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> >> +			     rc);
> >> +	else
> >> +		virtqueue_kick(vioch->vqueue);
> >> +
> >> +	spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +	return rc;
> >> +}
> >> +
> >> +static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> >> +{
> >> +	unsigned long ready_flags;
> >> +	unsigned long flags;
> >> +	unsigned int length;
> >> +	struct scmi_vio_channel *vioch;
> >> +	struct scmi_vio_msg *msg;
> >> +	bool cb_enabled = true;
> >> +
> >> +	if (WARN_ON_ONCE(!vqueue->vdev->priv))
> >> +		return;
> >> +	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
> >> +
> >> +	for (;;) {
> >> +		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
> >> +
> >> +		if (!vioch->ready) {
> >> +			if (!cb_enabled)
> >> +				(void)virtqueue_enable_cb(vqueue);
> >> +			goto unlock_ready_out;
> >> +		}
> >> +
> >> +		spin_lock_irqsave(&vioch->lock, flags);
> >> +		if (cb_enabled) {
> >> +			virtqueue_disable_cb(vqueue);
> >> +			cb_enabled = false;
> >> +		}
> >> +		msg = virtqueue_get_buf(vqueue, &length);
> >> +		if (!msg) {
> >> +			if (virtqueue_enable_cb(vqueue))
> >> +				goto unlock_out;
> >> +			else
> >> +				cb_enabled = true;
> >> +		}
> >> +		spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +		if (msg) {
> >> +			msg->rx_len = length;
> >> +
> >> +			/*
> >> +			 * Hold the ready_lock during the callback to avoid
> >> +			 * races when the arm-scmi driver is unbinding while
> >> +			 * the virtio device is not quiesced yet.
> >> +			 */
> >> +			scmi_rx_callback(vioch->cinfo,
> >> +					 msg_read_header(msg->input), msg);
> >> +		}
> >> +		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> >> +	}
> >> +
> >> +unlock_out:
> >> +	spin_unlock_irqrestore(&vioch->lock, flags);
> >> +unlock_ready_out:
> >> +	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
> >> +}
> >> +
> >> +static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
> >> +
> >> +static vq_callback_t *scmi_vio_complete_callbacks[] = {
> >> +	scmi_vio_complete_cb,
> >> +	scmi_vio_complete_cb
> >> +};
> >> +
> >> +static unsigned int virtio_get_max_msg(bool tx,
> >> +				       struct scmi_chan_info *base_cinfo)
> >> +{
> >> +	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
> >> +	unsigned int ret;
> >> +
> >> +	ret = virtqueue_get_vring_size(vioch->vqueue);
> >> +
> >> +	/* Tx messages need multiple descriptors. */
> >> +	if (tx)
> >> +		ret /= DESCRIPTORS_PER_TX_MSG;
> >> +
> >> +	if (ret > MSG_TOKEN_MAX) {
> >> +		dev_info_once(
> >> +			base_cinfo->dev,
> >> +			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
> >> +			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
> >> +		ret = MSG_TOKEN_MAX;
> >> +	}
> >> +
> >> +	return ret;
> >> +}
> >> +
> >> +static int scmi_vio_match_any_dev(struct device *dev, const void *data)
> >> +{
> >> +	return 1;
> >> +}
> >> +
> >> +static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
> >> +
> >> +static int virtio_link_supplier(struct device *dev)
> >> +{
> >> +	struct device *vdev = driver_find_device(
> >> +		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
> >> +
> >> +	if (!vdev) {
> >> +		dev_notice_once(
> >> +			dev,
> >> +			"Deferring probe after not finding a bound scmi-virtio device\n");
> >> +		return -EPROBE_DEFER;
> >> +	}
> >> +
> >> +	/* Add device link for remove order and sysfs link. */
> >> +	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
> >> +		put_device(vdev);
> >> +		dev_err(dev, "Adding link to supplier virtio device failed\n");
> >> +		return -ECANCELED;
> >> +	}
> >> +
> >> +	put_device(vdev);
> >> +	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
> >> +}
> >> +
> >> +static bool virtio_chan_available(struct device *dev, int idx)
> >> +{
> >> +	struct virtio_device *vdev;
> >> +
> >> +	/* scmi-virtio doesn't support per-protocol channels */
> >> +	if (is_scmi_protocol_device(dev))
> >> +		return false;
> >> +
> >> +	vdev = scmi_get_transport_info(dev);
> >> +	if (!vdev)
> >> +		return false;
> >> +
> >> +	switch (idx) {
> >> +	case VIRTIO_SCMI_VQ_TX:
> >> +		return true;
> >> +	case VIRTIO_SCMI_VQ_RX:
> >> +		return scmi_vio_have_vq_rx(vdev);
> >> +	default:
> >> +		return false;
> >> +	}
> >> +}
> >> +
> >> +static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> >> +			     bool tx)
> >> +{
> >> +	unsigned long flags;
> >> +	struct virtio_device *vdev;
> >> +	struct scmi_vio_channel *vioch;
> >> +	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> >> +	int max_msg;
> >> +	int i;
> >> +
> >> +	if (!virtio_chan_available(dev, index))
> >> +		return -ENODEV;
> >> +
> >> +	vdev = scmi_get_transport_info(dev);
> >> +	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
> >> +
> >> +	spin_lock_irqsave(&vioch->lock, flags);
> >> +	cinfo->transport_info = vioch;
> >> +	vioch->cinfo = cinfo;
> >> +	spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +	max_msg = virtio_get_max_msg(tx, cinfo);
> >> +
> >> +	for (i = 0; i < max_msg; i++) {
> >> +		struct scmi_vio_msg *msg;
> >> +
> >> +		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
> >> +		if (!msg)
> >> +			return -ENOMEM;
> >> +
> >> +		if (tx) {
> >> +			msg->request = devm_kzalloc(cinfo->dev,
> >> +						    VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +						    GFP_KERNEL);
> >> +			if (!msg->request)
> >> +				return -ENOMEM;
> >> +		}
> >> +
> >> +		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
> >> +					  GFP_KERNEL);
> >> +		if (!msg->input)
> >> +			return -ENOMEM;
> >> +
> >> +		if (tx) {
> >> +			spin_lock_irqsave(&vioch->lock, flags);
> >> +			list_add_tail(&msg->list, &vioch->free_list);
> >> +			spin_unlock_irqrestore(&vioch->lock, flags);
> >> +		} else {
> >> +			scmi_vio_feed_vq_rx(vioch, msg);
> >> +		}
> >> +	}
> >> +
> >> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +	vioch->ready = true;
> >> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static int virtio_chan_free(int id, void *p, void *data)
> >> +{
> >> +	unsigned long flags;
> >> +	struct scmi_chan_info *cinfo = p;
> >> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +	spin_lock_irqsave(&vioch->ready_lock, flags);
> >> +	vioch->ready = false;
> >> +	spin_unlock_irqrestore(&vioch->ready_lock, flags);
> >> +
> >> +	scmi_free_channel(cinfo, data, id);
> >> +	return 0;
> >> +}
> >> +
> >> +static int virtio_send_message(struct scmi_chan_info *cinfo,
> >> +			       struct scmi_xfer *xfer)
> >> +{
> >> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +	struct scatterlist sg_out;
> >> +	struct scatterlist sg_in;
> >> +	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
> >> +	unsigned long flags;
> >> +	int rc;
> >> +	struct scmi_vio_msg *msg;
> >> +
> >> +	/*
> >> +	 * TODO: For now, we don't support polling. But it should not be
> >> +	 * difficult to add support.
> >> +	 */
> >> +	if (xfer->hdr.poll_completion)
> >> +		return -EINVAL;
> >> +
> >> +	spin_lock_irqsave(&vioch->lock, flags);
> >> +
> >> +	if (list_empty(&vioch->free_list)) {
> >> +		spin_unlock_irqrestore(&vioch->lock, flags);
> >> +		return -EBUSY;
> >> +	}
> >> +
> >> +	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> >> +	list_del(&msg->list);
> >> +
> >> +	msg_tx_prepare(msg->request, xfer);
> >> +
> >> +	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> >> +	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
> >> +
> >> +	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> >> +	if (rc) {
> >> +		list_add(&msg->list, &vioch->free_list);
> >> +		dev_err_once(vioch->cinfo->dev,
> >> +			     "%s() failed to add to virtqueue (%d)\n", __func__,
> >> +			     rc);
> >> +	} else {
> >> +		virtqueue_kick(vioch->vqueue);
> >> +	}
> >> +
> >> +	spin_unlock_irqrestore(&vioch->lock, flags);
> >> +
> >> +	return rc;
> >> +}
> >> +
> >> +static void virtio_fetch_response(struct scmi_chan_info *cinfo,
> >> +				  struct scmi_xfer *xfer, void *msg_handle)
> >> +{
> >> +	struct scmi_vio_msg *msg = msg_handle;
> >> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +	if (!msg) {
> >> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +			     "Ignoring %s() call with NULL msg_handle\n",
> >> +			     __func__);
> >> +		return;
> >> +	}
> >> +
> >> +	msg_fetch_response(msg->input, msg->rx_len, xfer);
> >> +}
> >> +
> >> +static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
> >> +				      size_t max_len, struct scmi_xfer *xfer,
> >> +				      void *msg_handle)
> >> +{
> >> +	struct scmi_vio_msg *msg = msg_handle;
> >> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +
> >> +	if (!msg) {
> >> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +			     "Ignoring %s() call with NULL msg_handle\n",
> >> +			     __func__);
> >> +		return;
> >> +	}
> >> +
> >> +	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
> >> +}
> >> +
> >> +static void dummy_clear_channel(struct scmi_chan_info *cinfo)
> >> +{
> >> +}
> >> +
> >> +static bool dummy_poll_done(struct scmi_chan_info *cinfo,
> >> +			    struct scmi_xfer *xfer)
> >> +{
> >> +	return false;
> >> +}
> >> +
> >> +static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
> >> +{
> >> +	unsigned long flags;
> >> +	struct scmi_vio_channel *vioch = cinfo->transport_info;
> >> +	struct scmi_vio_msg *msg = msg_handle;
> >> +
> >> +	if (!msg) {
> >> +		dev_dbg_once(&vioch->vqueue->vdev->dev,
> >> +			     "Ignoring %s() call with NULL msg_handle\n",
> >> +			     __func__);
> >> +		return;
> >> +	}
> >> +
> >> +	if (vioch->is_rx) {
> >> +		scmi_vio_feed_vq_rx(vioch, msg);
> >> +	} else {
> >> +		spin_lock_irqsave(&vioch->lock, flags);
> >> +		list_add(&msg->list, &vioch->free_list);
> >> +		spin_unlock_irqrestore(&vioch->lock, flags);
> >> +	}
> >> +}
> >> +
> >> +static const struct scmi_transport_ops scmi_virtio_ops = {
> >> +	.link_supplier = virtio_link_supplier,
> >> +	.chan_available = virtio_chan_available,
> >> +	.chan_setup = virtio_chan_setup,
> >> +	.chan_free = virtio_chan_free,
> >> +	.get_max_msg = virtio_get_max_msg,
> >> +	.send_message = virtio_send_message,
> >> +	.fetch_response = virtio_fetch_response,
> >> +	.fetch_notification = virtio_fetch_notification,
> >> +	.clear_channel = dummy_clear_channel,
> >> +	.poll_done = dummy_poll_done,
> >> +	.drop_message = virtio_drop_message,
> >> +};
> >> +
> >> +static int scmi_vio_probe(struct virtio_device *vdev)
> >> +{
> >> +	struct device *dev = &vdev->dev;
> >> +	struct scmi_vio_channel *channels;
> >> +	bool have_vq_rx;
> >> +	int vq_cnt;
> >> +	int i;
> >> +	int ret;
> >> +	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
> >> +
> >> +	have_vq_rx = scmi_vio_have_vq_rx(vdev);
> >> +	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
> >> +
> >> +	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
> >> +	if (!channels)
> >> +		return -ENOMEM;
> >> +
> >> +	if (have_vq_rx)
> >> +		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
> >> +
> >> +	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
> >> +			      scmi_vio_vqueue_names, NULL);
> >> +	if (ret) {
> >> +		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
> >> +		return ret;
> >> +	}
> >> +	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
> >> +
> >> +	for (i = 0; i < vq_cnt; i++) {
> >> +		spin_lock_init(&channels[i].lock);
> >> +		spin_lock_init(&channels[i].ready_lock);
> >> +		INIT_LIST_HEAD(&channels[i].free_list);
> >> +		channels[i].vqueue = vqs[i];
> >> +	}
> >> +
> >> +	vdev->priv = channels;
> >> +
> >> +	return 0;
> >> +}
> >> +
> >> +static void scmi_vio_remove(struct virtio_device *vdev)
> >> +{
> >> +	vdev->config->reset(vdev);
> >> +	vdev->config->del_vqs(vdev);
> >> +}
> >> +
> >> +static unsigned int features[] = {
> >> +	VIRTIO_SCMI_F_P2A_CHANNELS,
> >> +};
> >> +
> >> +static const struct virtio_device_id id_table[] = {
> >> +	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
> >> +	{ 0 }
> >> +};
> >> +
> >> +static struct virtio_driver virtio_scmi_driver = {
> >> +	.driver.name = "scmi-virtio",
> >> +	.driver.owner = THIS_MODULE,
> >> +	.feature_table = features,
> >> +	.feature_table_size = ARRAY_SIZE(features),
> >> +	.id_table = id_table,
> >> +	.probe = scmi_vio_probe,
> >> +	.remove = scmi_vio_remove,
> >> +};
> >> +
> >> +static int __init virtio_scmi_init(void)
> >> +{
> >> +	return register_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +static void __exit virtio_scmi_exit(void)
> >> +{
> >> +	unregister_virtio_driver(&virtio_scmi_driver);
> >> +}
> >> +
> >> +const struct scmi_desc scmi_virtio_desc = {
> >> +	.init = virtio_scmi_init,
> >> +	.exit = virtio_scmi_exit,
> >> +	.ops = &scmi_virtio_ops,
> >> +	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
> >> +	.max_msg = 0, /* overridden by virtio_get_max_msg() */
> >> +	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
> >> +};
> >> diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
> >> index f0c35ce8628c..c146fe30e589 100644
> >> --- a/include/uapi/linux/virtio_ids.h
> >> +++ b/include/uapi/linux/virtio_ids.h
> >> @@ -56,5 +56,6 @@
> >>  #define VIRTIO_ID_PMEM			27 /* virtio pmem */
> >>  #define VIRTIO_ID_BT			28 /* virtio bluetooth */
> >>  #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
> >> +#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
> >>  
> >>  #endif /* _LINUX_VIRTIO_IDS_H */
> >> diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
> >> new file mode 100644
> >> index 000000000000..732b01504c35
> >> --- /dev/null
> >> +++ b/include/uapi/linux/virtio_scmi.h
> >> @@ -0,0 +1,25 @@
> >> +/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
> >> +/*
> >> + * Copyright (C) 2020 OpenSynergy GmbH
> >> + */
> >> +
> >> +#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
> >> +#define _UAPI_LINUX_VIRTIO_SCMI_H
> >> +
> >> +#include <linux/virtio_types.h>
> >> +
> >> +/* Feature bits */
> >> +
> >> +/* Device implements some SCMI notifications, or delayed responses. */
> >> +#define VIRTIO_SCMI_F_P2A_CHANNELS 0
> >> +
> >> +/* Device implements any SCMI statistics shared memory region */
> >> +#define VIRTIO_SCMI_F_SHARED_MEMORY 1
> >> +
> >> +/* Virtqueues */
> >> +
> >> +#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
> >> +#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
> >> +#define VIRTIO_SCMI_VQ_MAX_CNT 2
> >> +
> >> +#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */
> >> -- 
> >> 2.25.1
> >>
> >>
> > 
> 
>

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index bd7aff0c120f..449c336872f3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17705,6 +17705,7 @@  F:	drivers/regulator/scmi-regulator.c
 F:	drivers/reset/reset-scmi.c
 F:	include/linux/sc[mp]i_protocol.h
 F:	include/trace/events/scmi.h
+F:	include/uapi/linux/virtio_scmi.h
 
 SYSTEM RESET/SHUTDOWN DRIVERS
 M:	Sebastian Reichel <[e-mail]>
diff --git a/drivers/firmware/Kconfig b/drivers/firmware/Kconfig
index e8377b12e4d0..7e9eafdd9b63 100644
--- a/drivers/firmware/Kconfig
+++ b/drivers/firmware/Kconfig
@@ -39,6 +39,18 @@  config ARM_SCMI_HAVE_MSG
 	  This declares whether a message passing based transport for SCMI is
 	  available.
 
+# This config option includes the dependencies of ARM_SCMI_PROTOCOL so that
+# this config doesn't show up when SCMI wouldn't be available.
+config VIRTIO_SCMI
+	bool "Virtio transport for SCMI"
+	select ARM_SCMI_HAVE_MSG
+	depends on VIRTIO && (ARM || ARM64 || COMPILE_TEST)
+	help
+	  This enables the virtio based transport for SCMI.
+
+	  If you want to use the ARM SCMI protocol between the virtio guest and
+	  a host providing a virtio SCMI device, answer Y.
+
 config ARM_SCMI_POWER_DOMAIN
 	tristate "SCMI power domain driver"
 	depends on ARM_SCMI_PROTOCOL || (COMPILE_TEST && OF)
diff --git a/drivers/firmware/arm_scmi/Makefile b/drivers/firmware/arm_scmi/Makefile
index f6b4acb8abdb..db1787606fb2 100644
--- a/drivers/firmware/arm_scmi/Makefile
+++ b/drivers/firmware/arm_scmi/Makefile
@@ -5,6 +5,7 @@  scmi-transport-$(CONFIG_ARM_SCMI_HAVE_SHMEM) = shmem.o
 scmi-transport-$(CONFIG_MAILBOX) += mailbox.o
 scmi-transport-$(CONFIG_HAVE_ARM_SMCCC_DISCOVERY) += smc.o
 scmi-transport-$(CONFIG_ARM_SCMI_HAVE_MSG) += msg.o
+scmi-transport-$(CONFIG_VIRTIO_SCMI) += virtio.o
 scmi-protocols-y = base.o clock.o perf.o power.o reset.o sensors.o system.o voltage.o
 scmi-module-objs := $(scmi-bus-y) $(scmi-driver-y) $(scmi-protocols-y) \
 		    $(scmi-transport-y)
diff --git a/drivers/firmware/arm_scmi/common.h b/drivers/firmware/arm_scmi/common.h
index 4cb6571c7aaf..bada06cfd33d 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -349,6 +349,9 @@  extern const struct scmi_desc scmi_mailbox_desc;
 #ifdef CONFIG_HAVE_ARM_SMCCC
 extern const struct scmi_desc scmi_smc_desc;
 #endif
+#ifdef CONFIG_VIRTIO_SCMI
+extern const struct scmi_desc scmi_virtio_desc;
+#endif
 
 int scmi_set_transport_info(struct device *dev, void *transport_info);
 void *scmi_get_transport_info(struct device *dev);
diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
index e04e7c8e6928..a31187385470 100644
--- a/drivers/firmware/arm_scmi/driver.c
+++ b/drivers/firmware/arm_scmi/driver.c
@@ -1637,6 +1637,9 @@  static const struct of_device_id scmi_of_match[] = {
 #endif
 #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
 	{ .compatible = "arm,scmi-smc", .data = &scmi_smc_desc},
+#endif
+#ifdef CONFIG_VIRTIO_SCMI
+	{ .compatible = "arm,scmi-virtio", .data = &scmi_virtio_desc},
 #endif
 	{ /* Sentinel */ },
 };
diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
new file mode 100644
index 000000000000..20972adf6dc7
--- /dev/null
+++ b/drivers/firmware/arm_scmi/virtio.c
@@ -0,0 +1,523 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Virtio Transport driver for Arm System Control and Management Interface
+ * (SCMI).
+ *
+ * Copyright (C) 2020 OpenSynergy.
+ */
+
+/**
+ * DOC: Theory of Operation
+ *
+ * The scmi-virtio transport implements a driver for the virtio SCMI device.
+ *
+ * There is one Tx channel (virtio cmdq, A2P channel) and at most one Rx
+ * channel (virtio eventq, P2A channel). Each channel is implemented through a
+ * virtqueue. Access to each virtqueue is protected by spinlocks.
+ */
+
+#include <linux/errno.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/virtio.h>
+#include <linux/virtio_config.h>
+#include <uapi/linux/virtio_ids.h>
+#include <uapi/linux/virtio_scmi.h>
+
+#include "common.h"
+
+#define VIRTIO_SCMI_MAX_MSG_SIZE 128 /* Value may be increased. */
+#define VIRTIO_SCMI_MAX_PDU_SIZE \
+	(VIRTIO_SCMI_MAX_MSG_SIZE + SCMI_MSG_MAX_PROT_OVERHEAD)
+#define DESCRIPTORS_PER_TX_MSG 2
+
+/**
+ * struct scmi_vio_channel - Transport channel information
+ *
+ * @lock: Protects access to all members except ready.
+ * @ready_lock: Protects access to ready. If required, it must be taken before
+ *              lock.
+ * @vqueue: Associated virtqueue
+ * @cinfo: SCMI Tx or Rx channel
+ * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
+ * @is_rx: Whether channel is an Rx channel
+ * @ready: Whether transport user is ready to hear about channel
+ */
+struct scmi_vio_channel {
+	spinlock_t lock;
+	spinlock_t ready_lock;
+	struct virtqueue *vqueue;
+	struct scmi_chan_info *cinfo;
+	struct list_head free_list;
+	u8 is_rx;
+	u8 ready;
+};
+
+/**
+ * struct scmi_vio_msg - Transport PDU information
+ *
+ * @request: SDU used for commands
+ * @input: SDU used for (delayed) responses and notifications
+ * @list: List which scmi_vio_msg may be part of
+ * @rx_len: Input SDU size in bytes, once input has been received
+ */
+struct scmi_vio_msg {
+	struct scmi_msg_payld *request;
+	struct scmi_msg_payld *input;
+	struct list_head list;
+	unsigned int rx_len;
+};
+
+static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
+{
+	return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
+}
+
+static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
+			       struct scmi_vio_msg *msg)
+{
+	struct scatterlist sg_in;
+	int rc;
+	unsigned long flags;
+
+	sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
+
+	spin_lock_irqsave(&vioch->lock, flags);
+
+	rc = virtqueue_add_inbuf(vioch->vqueue, &sg_in, 1, msg, GFP_ATOMIC);
+	if (rc)
+		dev_err_once(vioch->cinfo->dev,
+			     "%s() failed to add to virtqueue (%d)\n", __func__,
+			     rc);
+	else
+		virtqueue_kick(vioch->vqueue);
+
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	return rc;
+}
+
+static void scmi_vio_complete_cb(struct virtqueue *vqueue)
+{
+	unsigned long ready_flags;
+	unsigned long flags;
+	unsigned int length;
+	struct scmi_vio_channel *vioch;
+	struct scmi_vio_msg *msg;
+	bool cb_enabled = true;
+
+	if (WARN_ON_ONCE(!vqueue->vdev->priv))
+		return;
+	vioch = &((struct scmi_vio_channel *)vqueue->vdev->priv)[vqueue->index];
+
+	for (;;) {
+		spin_lock_irqsave(&vioch->ready_lock, ready_flags);
+
+		if (!vioch->ready) {
+			if (!cb_enabled)
+				(void)virtqueue_enable_cb(vqueue);
+			goto unlock_ready_out;
+		}
+
+		spin_lock_irqsave(&vioch->lock, flags);
+		if (cb_enabled) {
+			virtqueue_disable_cb(vqueue);
+			cb_enabled = false;
+		}
+		msg = virtqueue_get_buf(vqueue, &length);
+		if (!msg) {
+			if (virtqueue_enable_cb(vqueue))
+				goto unlock_out;
+			else
+				cb_enabled = true;
+		}
+		spin_unlock_irqrestore(&vioch->lock, flags);
+
+		if (msg) {
+			msg->rx_len = length;
+
+			/*
+			 * Hold the ready_lock during the callback to avoid
+			 * races when the arm-scmi driver is unbinding while
+			 * the virtio device is not quiesced yet.
+			 */
+			scmi_rx_callback(vioch->cinfo,
+					 msg_read_header(msg->input), msg);
+		}
+		spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+	}
+
+unlock_out:
+	spin_unlock_irqrestore(&vioch->lock, flags);
+unlock_ready_out:
+	spin_unlock_irqrestore(&vioch->ready_lock, ready_flags);
+}
+
+static const char *const scmi_vio_vqueue_names[] = { "tx", "rx" };
+
+static vq_callback_t *scmi_vio_complete_callbacks[] = {
+	scmi_vio_complete_cb,
+	scmi_vio_complete_cb
+};
+
+static unsigned int virtio_get_max_msg(bool tx,
+				       struct scmi_chan_info *base_cinfo)
+{
+	struct scmi_vio_channel *vioch = base_cinfo->transport_info;
+	unsigned int ret;
+
+	ret = virtqueue_get_vring_size(vioch->vqueue);
+
+	/* Tx messages need multiple descriptors. */
+	if (tx)
+		ret /= DESCRIPTORS_PER_TX_MSG;
+
+	if (ret > MSG_TOKEN_MAX) {
+		dev_info_once(
+			base_cinfo->dev,
+			"Only %ld messages can be pending simultaneously, while the %s virtqueue could hold %d\n",
+			MSG_TOKEN_MAX, tx ? "tx" : "rx", ret);
+		ret = MSG_TOKEN_MAX;
+	}
+
+	return ret;
+}
+
+static int scmi_vio_match_any_dev(struct device *dev, const void *data)
+{
+	return 1;
+}
+
+static struct virtio_driver virtio_scmi_driver; /* Forward declaration */
+
+static int virtio_link_supplier(struct device *dev)
+{
+	struct device *vdev = driver_find_device(
+		&virtio_scmi_driver.driver, NULL, NULL, scmi_vio_match_any_dev);
+
+	if (!vdev) {
+		dev_notice_once(
+			dev,
+			"Deferring probe after not finding a bound scmi-virtio device\n");
+		return -EPROBE_DEFER;
+	}
+
+	/* Add device link for remove order and sysfs link. */
+	if (!device_link_add(dev, vdev, DL_FLAG_AUTOREMOVE_CONSUMER)) {
+		put_device(vdev);
+		dev_err(dev, "Adding link to supplier virtio device failed\n");
+		return -ECANCELED;
+	}
+
+	put_device(vdev);
+	return scmi_set_transport_info(dev, dev_to_virtio(vdev));
+}
+
+static bool virtio_chan_available(struct device *dev, int idx)
+{
+	struct virtio_device *vdev;
+
+	/* scmi-virtio doesn't support per-protocol channels */
+	if (is_scmi_protocol_device(dev))
+		return false;
+
+	vdev = scmi_get_transport_info(dev);
+	if (!vdev)
+		return false;
+
+	switch (idx) {
+	case VIRTIO_SCMI_VQ_TX:
+		return true;
+	case VIRTIO_SCMI_VQ_RX:
+		return scmi_vio_have_vq_rx(vdev);
+	default:
+		return false;
+	}
+}
+
+static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
+			     bool tx)
+{
+	unsigned long flags;
+	struct virtio_device *vdev;
+	struct scmi_vio_channel *vioch;
+	int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
+	int max_msg;
+	int i;
+
+	if (!virtio_chan_available(dev, index))
+		return -ENODEV;
+
+	vdev = scmi_get_transport_info(dev);
+	vioch = &((struct scmi_vio_channel *)vdev->priv)[index];
+
+	spin_lock_irqsave(&vioch->lock, flags);
+	cinfo->transport_info = vioch;
+	vioch->cinfo = cinfo;
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	max_msg = virtio_get_max_msg(tx, cinfo);
+
+	for (i = 0; i < max_msg; i++) {
+		struct scmi_vio_msg *msg;
+
+		msg = devm_kzalloc(cinfo->dev, sizeof(*msg), GFP_KERNEL);
+		if (!msg)
+			return -ENOMEM;
+
+		if (tx) {
+			msg->request = devm_kzalloc(cinfo->dev,
+						    VIRTIO_SCMI_MAX_PDU_SIZE,
+						    GFP_KERNEL);
+			if (!msg->request)
+				return -ENOMEM;
+		}
+
+		msg->input = devm_kzalloc(cinfo->dev, VIRTIO_SCMI_MAX_PDU_SIZE,
+					  GFP_KERNEL);
+		if (!msg->input)
+			return -ENOMEM;
+
+		if (tx) {
+			spin_lock_irqsave(&vioch->lock, flags);
+			list_add_tail(&msg->list, &vioch->free_list);
+			spin_unlock_irqrestore(&vioch->lock, flags);
+		} else {
+			scmi_vio_feed_vq_rx(vioch, msg);
+		}
+	}
+
+	spin_lock_irqsave(&vioch->ready_lock, flags);
+	vioch->ready = true;
+	spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+	return 0;
+}
+
+static int virtio_chan_free(int id, void *p, void *data)
+{
+	unsigned long flags;
+	struct scmi_chan_info *cinfo = p;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+	spin_lock_irqsave(&vioch->ready_lock, flags);
+	vioch->ready = false;
+	spin_unlock_irqrestore(&vioch->ready_lock, flags);
+
+	scmi_free_channel(cinfo, data, id);
+	return 0;
+}
+
+static int virtio_send_message(struct scmi_chan_info *cinfo,
+			       struct scmi_xfer *xfer)
+{
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scatterlist sg_out;
+	struct scatterlist sg_in;
+	struct scatterlist *sgs[DESCRIPTORS_PER_TX_MSG] = { &sg_out, &sg_in };
+	unsigned long flags;
+	int rc;
+	struct scmi_vio_msg *msg;
+
+	/*
+	 * TODO: For now, we don't support polling. But it should not be
+	 * difficult to add support.
+	 */
+	if (xfer->hdr.poll_completion)
+		return -EINVAL;
+
+	spin_lock_irqsave(&vioch->lock, flags);
+
+	if (list_empty(&vioch->free_list)) {
+		spin_unlock_irqrestore(&vioch->lock, flags);
+		return -EBUSY;
+	}
+
+	msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
+	list_del(&msg->list);
+
+	msg_tx_prepare(msg->request, xfer);
+
+	sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
+	sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
+
+	rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
+	if (rc) {
+		list_add(&msg->list, &vioch->free_list);
+		dev_err_once(vioch->cinfo->dev,
+			     "%s() failed to add to virtqueue (%d)\n", __func__,
+			     rc);
+	} else {
+		virtqueue_kick(vioch->vqueue);
+	}
+
+	spin_unlock_irqrestore(&vioch->lock, flags);
+
+	return rc;
+}
+
+static void virtio_fetch_response(struct scmi_chan_info *cinfo,
+				  struct scmi_xfer *xfer, void *msg_handle)
+{
+	struct scmi_vio_msg *msg = msg_handle;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+	if (!msg) {
+		dev_dbg_once(&vioch->vqueue->vdev->dev,
+			     "Ignoring %s() call with NULL msg_handle\n",
+			     __func__);
+		return;
+	}
+
+	msg_fetch_response(msg->input, msg->rx_len, xfer);
+}
+
+static void virtio_fetch_notification(struct scmi_chan_info *cinfo,
+				      size_t max_len, struct scmi_xfer *xfer,
+				      void *msg_handle)
+{
+	struct scmi_vio_msg *msg = msg_handle;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+
+	if (!msg) {
+		dev_dbg_once(&vioch->vqueue->vdev->dev,
+			     "Ignoring %s() call with NULL msg_handle\n",
+			     __func__);
+		return;
+	}
+
+	msg_fetch_notification(msg->input, msg->rx_len, max_len, xfer);
+}
+
+static void dummy_clear_channel(struct scmi_chan_info *cinfo)
+{
+}
+
+static bool dummy_poll_done(struct scmi_chan_info *cinfo,
+			    struct scmi_xfer *xfer)
+{
+	return false;
+}
+
+static void virtio_drop_message(struct scmi_chan_info *cinfo, void *msg_handle)
+{
+	unsigned long flags;
+	struct scmi_vio_channel *vioch = cinfo->transport_info;
+	struct scmi_vio_msg *msg = msg_handle;
+
+	if (!msg) {
+		dev_dbg_once(&vioch->vqueue->vdev->dev,
+			     "Ignoring %s() call with NULL msg_handle\n",
+			     __func__);
+		return;
+	}
+
+	if (vioch->is_rx) {
+		scmi_vio_feed_vq_rx(vioch, msg);
+	} else {
+		spin_lock_irqsave(&vioch->lock, flags);
+		list_add(&msg->list, &vioch->free_list);
+		spin_unlock_irqrestore(&vioch->lock, flags);
+	}
+}
+
+static const struct scmi_transport_ops scmi_virtio_ops = {
+	.link_supplier = virtio_link_supplier,
+	.chan_available = virtio_chan_available,
+	.chan_setup = virtio_chan_setup,
+	.chan_free = virtio_chan_free,
+	.get_max_msg = virtio_get_max_msg,
+	.send_message = virtio_send_message,
+	.fetch_response = virtio_fetch_response,
+	.fetch_notification = virtio_fetch_notification,
+	.clear_channel = dummy_clear_channel,
+	.poll_done = dummy_poll_done,
+	.drop_message = virtio_drop_message,
+};
+
+static int scmi_vio_probe(struct virtio_device *vdev)
+{
+	struct device *dev = &vdev->dev;
+	struct scmi_vio_channel *channels;
+	bool have_vq_rx;
+	int vq_cnt;
+	int i;
+	int ret;
+	struct virtqueue *vqs[VIRTIO_SCMI_VQ_MAX_CNT];
+
+	have_vq_rx = scmi_vio_have_vq_rx(vdev);
+	vq_cnt = have_vq_rx ? VIRTIO_SCMI_VQ_MAX_CNT : 1;
+
+	channels = devm_kcalloc(dev, vq_cnt, sizeof(*channels), GFP_KERNEL);
+	if (!channels)
+		return -ENOMEM;
+
+	if (have_vq_rx)
+		channels[VIRTIO_SCMI_VQ_RX].is_rx = true;
+
+	ret = virtio_find_vqs(vdev, vq_cnt, vqs, scmi_vio_complete_callbacks,
+			      scmi_vio_vqueue_names, NULL);
+	if (ret) {
+		dev_err(dev, "Failed to get %d virtqueue(s)\n", vq_cnt);
+		return ret;
+	}
+	dev_info(dev, "Found %d virtqueue(s)\n", vq_cnt);
+
+	for (i = 0; i < vq_cnt; i++) {
+		spin_lock_init(&channels[i].lock);
+		spin_lock_init(&channels[i].ready_lock);
+		INIT_LIST_HEAD(&channels[i].free_list);
+		channels[i].vqueue = vqs[i];
+	}
+
+	vdev->priv = channels;
+
+	return 0;
+}
+
+static void scmi_vio_remove(struct virtio_device *vdev)
+{
+	vdev->config->reset(vdev);
+	vdev->config->del_vqs(vdev);
+}
+
+static unsigned int features[] = {
+	VIRTIO_SCMI_F_P2A_CHANNELS,
+};
+
+static const struct virtio_device_id id_table[] = {
+	{ VIRTIO_ID_SCMI, VIRTIO_DEV_ANY_ID },
+	{ 0 }
+};
+
+static struct virtio_driver virtio_scmi_driver = {
+	.driver.name = "scmi-virtio",
+	.driver.owner = THIS_MODULE,
+	.feature_table = features,
+	.feature_table_size = ARRAY_SIZE(features),
+	.id_table = id_table,
+	.probe = scmi_vio_probe,
+	.remove = scmi_vio_remove,
+};
+
+static int __init virtio_scmi_init(void)
+{
+	return register_virtio_driver(&virtio_scmi_driver);
+}
+
+static void __exit virtio_scmi_exit(void)
+{
+	unregister_virtio_driver(&virtio_scmi_driver);
+}
+
+const struct scmi_desc scmi_virtio_desc = {
+	.init = virtio_scmi_init,
+	.exit = virtio_scmi_exit,
+	.ops = &scmi_virtio_ops,
+	.max_rx_timeout_ms = 60000, /* for non-realtime virtio devices */
+	.max_msg = 0, /* overridden by virtio_get_max_msg() */
+	.max_msg_size = VIRTIO_SCMI_MAX_MSG_SIZE,
+};
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index f0c35ce8628c..c146fe30e589 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -56,5 +56,6 @@ 
 #define VIRTIO_ID_PMEM			27 /* virtio pmem */
 #define VIRTIO_ID_BT			28 /* virtio bluetooth */
 #define VIRTIO_ID_MAC80211_HWSIM	29 /* virtio mac80211-hwsim */
+#define VIRTIO_ID_SCMI			32 /* virtio SCMI */
 
 #endif /* _LINUX_VIRTIO_IDS_H */
diff --git a/include/uapi/linux/virtio_scmi.h b/include/uapi/linux/virtio_scmi.h
new file mode 100644
index 000000000000..732b01504c35
--- /dev/null
+++ b/include/uapi/linux/virtio_scmi.h
@@ -0,0 +1,25 @@ 
+/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
+/*
+ * Copyright (C) 2020 OpenSynergy GmbH
+ */
+
+#ifndef _UAPI_LINUX_VIRTIO_SCMI_H
+#define _UAPI_LINUX_VIRTIO_SCMI_H
+
+#include <linux/virtio_types.h>
+
+/* Feature bits */
+
+/* Device implements some SCMI notifications, or delayed responses. */
+#define VIRTIO_SCMI_F_P2A_CHANNELS 0
+
+/* Device implements any SCMI statistics shared memory region */
+#define VIRTIO_SCMI_F_SHARED_MEMORY 1
+
+/* Virtqueues */
+
+#define VIRTIO_SCMI_VQ_TX 0 /* cmdq */
+#define VIRTIO_SCMI_VQ_RX 1 /* eventq */
+#define VIRTIO_SCMI_VQ_MAX_CNT 2
+
+#endif /* _UAPI_LINUX_VIRTIO_SCMI_H */