[1/6] spi: add flow controll support

Commit Message

Oleksij Rempel March 1, 2016, 2:43 p.m. UTC

Different HW implement different variants of SPI based flow control (FC).
To flexible FC implementation a spited it to fallowing common parts:
Flow control: Request Sequence
Master CS   |-------2\_____________________|
Slave  FC   |-----1\_______________________|
DATA        |-----------3\_________________|

Flow control: Ready Sequence
Master CS   |-----1\_______________________|
Slave  FC   |--------2\____________________|
DATA        |-----------3\_________________|

Flow control: ACK End of Data
Master CS   |______________________/2------|
Slave  FC   |________________________/3----|
DATA        |__________________/1----------|

Flow control: Pause
Master CS   |_______________________/------|
Slave  FC   |_______1/-----\3______/-------|
DATA        |________2/------\4___/--------|

Flow control: Ready signal on MISO
Master CS   |-----1\_______________________|
MISO/DATA   |------2\____3/----------------|
CONV START  |       ^                      |
DATA READY  |             ^                |

Signed-off-by: Oleksij Rempel <[e-mail]>
---
 Documentation/devicetree/bindings/spi/spi-bus.txt |   7 +
 drivers/spi/spi.c                                 | 191 +++++++++++++++++++++-
 include/linux/spi/spi.h                           |  68 +++++++-
 3 files changed, 261 insertions(+), 5 deletions(-)

Comments

Mark Brown March 2, 2016, 1:32 a.m. UTC | #1

On Tue, Mar 01, 2016 at 03:43:15PM +0100, Oleksij Rempel wrote:
> Different HW implement different variants of SPI based flow control (FC).
> To flexible FC implementation a spited it to fallowing common parts:

Please don't bury new patches in reply to the middle of some other
thread, it makes it really hard to follow what's going on.

Mark Brown March 2, 2016, 2:46 a.m. UTC | #2

On Tue, Mar 01, 2016 at 03:43:15PM +0100, Oleksij Rempel wrote:

At a high level I think this needs splitting up quite a bit - this is
defining a new DT binding, a new core interface for controlling flow
control and a bitbanging flow control implementation.  At least those
three bits should probably be separate patches, it may make sense to
split up the bitbanging implementation some more too.

> Different HW implement different variants of SPI based flow control (FC).
> To flexible FC implementation a spited it to fallowing common parts:
> Flow control: Request Sequence
> Master CS   |-------2\_____________________|
> Slave  FC   |-----1\_______________________|
> DATA        |-----------3\_________________|

I don't know what these pictures mean since you don't say what "slave
FC" is - I'm assuming you mean a separate pin but you need to specify
that.  It really looks like this would be clearer with words rather than
ASCII art.

In the case above this looks like a normal interrupt from a device, I'm
not clear what is different here or why this is in the core?

> Flow control: ACK End of Data
> Master CS   |______________________/2------|
> Slave  FC   |________________________/3----|
> DATA        |__________________/1----------|

Why would anything care about this case and why is it part of the SPI
protocol rather than something that the device driver would do?

> +	if (atomic_read(&spi->active_rq)) {
> +		if (!spi_fc_equal_cs(spi))
> +			dev_warn(&spi->dev, "Got request, but device is not ready\n");
> +		atomic_set(&spi->active_rq, 0);
> +		return ret;
> +	}

Atomic operations are very hard to use safely, you need to really spell
out what you think this is doing from a synchronization point of view
and why it's safe.

> +	if (spi->mode | SPI_FC_REQUEST &&
> +			!spi->cs_enabled && fc_enabled) {
> +		atomic_set(&spi->active_rq, 1);
> +		if (spi->request_cb)
> +			spi->request_cb(spi);

This logic is all too complicated for me to follow.  Why are we oring
things with spi->mode?

> +	struct device_node *np = spi->dev.of_node;
> +	int ret;
> +
> +	if (!np)
> +		return 0;

We can't support things only for DT, we need a way for things to be used
on other systemms.

Mark Brown March 2, 2016, 10:55 a.m. UTC | #3

On Wed, Mar 02, 2016 at 07:48:55AM +0100, fixed-term.Oleksij.Rempel wrote:
> On 02.03.2016 03:46, Mark Brown wrote:
> > On Tue, Mar 01, 2016 at 03:43:15PM +0100, Oleksij Rempel wrote:

> > In the case above this looks like a normal interrupt from a device, I'm
> > not clear what is different here or why this is in the core?

> At least our HW use tree different signals for flow control. One of it
> is Request Signal.

That's still an interrupt, just on a different line to the main
interrupt.

> >> Flow control: ACK End of Data
> >> Master CS   |______________________/2------|
> >> Slave  FC   |________________________/3----|
> >> DATA        |__________________/1----------|

> > Why would anything care about this case and why is it part of the SPI
> > protocol rather than something that the device driver would do?

> This case covers real bugs and in our case we need to detect if master
> or slave stalls under one second. If communication problem is detected,
> some of recovery scenarios is initiated. Like i said, this protocol is
> used for automotive industry.

That doesn't answer the second part of my question.  This doesn't seem
to be something that's anything to do with SPI, it's just your device
signalling things out of band.

> Please see two attached screen shots of Master and Slave initiated
> transfers.

Those tell me nothing.

> > Atomic operations are very hard to use safely, you need to really spell
> > out what you think this is doing from a synchronization point of view
> > and why it's safe.

> I'm trying to detect if we are on Master or Slave initiated transfer,
> which was detected by spi_fc_rq. Normally there should be no other
> interrupts on FC line and active_rq should not be changed until this
> transfer was processed. The "if (!spi_fc_equal_cs(spi))" check is in
> case my assumption is wrong or there is some HW issue. Do you have other
> suggestions?

Among other things it really needs to be crystal clear how this update
gets propagated to all CPUs in the system with no race conditions.

> >> +	if (spi->mode | SPI_FC_REQUEST &&
> >> +			!spi->cs_enabled && fc_enabled) {
> >> +		atomic_set(&spi->active_rq, 1);
> >> +		if (spi->request_cb)
> >> +			spi->request_cb(spi);

> > This logic is all too complicated for me to follow.  Why are we oring
> > things with spi->mode?

> I'm trying to checking here if fallowing case is actually expected by
> slave device. Other suggestions?

In what way are we checking what?  The code is incomprehensible.

Again, you're ignoring my specific question about the or.

> > We can't support things only for DT, we need a way for things to be used
> > on other systemms.

> I have nothing against it, but i even do not have other HW to test if my
> assumptions are correct. Would you accept untested code? :)

In general the way we do DT code is that the DT parses into some data
structure and then we work with that data structure.  This means that
everyone's code path is tested.

Patch

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index bbaa857..dfefc86 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -61,6 +61,13 @@  contain the following properties.
                       used for MOSI. Defaults to 1 if not present.
 - spi-rx-bus-width - (optional) The bus width(number of data wires) that
                       used for MISO. Defaults to 1 if not present.
+- spi-fc-ready      - (optional) flow control line used for ready signal.
+- spi-fc-stop-ack   - (optional) flow control line used to ACK end of transfer.
+- spi-fc-pause      - (optional) flow control line used for to pause transfer
+                      at any time.
+- spi-fc-request    - (optional) flow control line used for request signal.
+- spi-fc-miso-ready - (optional) MISO used for flow control ready signal.
+- fc-gpio           - (optional) gpio for flow control.
 
 Some SPI controllers and devices support Dual and Quad SPI transfer mode.
 It allows data in the SPI system to be transferred in 2 wires(DUAL) or 4 wires(QUAD).
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 47eff80..1140665 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -37,6 +37,8 @@ 
 #include <linux/kthread.h>
 #include <linux/ioport.h>
 #include <linux/acpi.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/spi.h>
@@ -396,6 +398,156 @@  int __spi_register_driver(struct module *owner, struct spi_driver *sdrv)
 EXPORT_SYMBOL_GPL(__spi_register_driver);
 
 /*-------------------------------------------------------------------------*/
+/*
+ * SPI flow control
+ */
+static int spi_fc_wait_miso(struct spi_device *spi)
+{
+	struct spi_master *master = spi->master;
+	int count = 100; /* 10 * 100 = 10 msec */
+
+	if (!master->get_miso_level)
+		return count;
+
+	while (count > 0) {
+		count--;
+		if (master->get_miso_level(spi))
+			break;
+
+		usleep_range(100, 200);
+	}
+
+	return count;
+}
+
+
+static int spi_fc_equal_cs(struct spi_device *spi)
+{
+	int fc_enabled;
+
+	fc_enabled = gpiod_get_value(spi->fc_gpio);
+	return (spi->cs_enabled == fc_enabled);
+}
+
+int spi_fc_wait_rq(struct spi_device *spi, u32 fc_state)
+{
+	unsigned long timeout = msecs_to_jiffies(10);
+	int ret = 1;
+
+	if (!(spi->mode & fc_state))
+		return ret;
+
+	if (spi->mode & SPI_FC_MISO_READY)
+		return spi_fc_wait_miso(spi);
+
+	if (atomic_read(&spi->active_rq)) {
+		if (!spi_fc_equal_cs(spi))
+			dev_warn(&spi->dev, "Got request, but device is not ready\n");
+		atomic_set(&spi->active_rq, 0);
+		return ret;
+	}
+
+	if (spi->fc_irq >= 0) {
+		ret = wait_for_completion_io_timeout(&spi->fc_complete,
+						     timeout);
+	} else {
+		int count = 100; /* 10 * 100 = 10-20 msec */
+
+		while (count > 0) {
+			count--;
+			if (spi_fc_equal_cs(spi))
+				break;
+
+			usleep_range(100, 200);
+		}
+		ret = count;
+	}
+
+	if (!ret)
+		dev_warn(&spi->dev, "FC timeout: requested state: 0x%x\n", fc_state);
+
+	return ret;
+}
+
+static irqreturn_t spi_fc_rq(int irq, void *dev_id)
+{
+	struct spi_device *spi = (struct spi_device *)dev_id;
+	int fc_enabled;
+
+	fc_enabled = gpiod_get_value(spi->fc_gpio);
+
+	if (spi->mode | SPI_FC_REQUEST &&
+			!spi->cs_enabled && fc_enabled) {
+		atomic_set(&spi->active_rq, 1);
+		if (spi->request_cb)
+			spi->request_cb(spi);
+	} else if (spi->mode | SPI_FC_STOP_ACK &&
+			!spi->cs_enabled && !fc_enabled) {
+		complete(&spi->fc_complete);
+	} else if (spi->mode | SPI_FC_READY &&
+			spi->cs_enabled && fc_enabled) {
+		complete(&spi->fc_complete);
+	} else {
+		dev_warn(&spi->dev, "Wrong FC State. CS:%i, FC:%i, Mode:0x%x\n",
+			 spi->cs_enabled, fc_enabled, spi->mode);
+	}
+
+	return IRQ_HANDLED;
+}
+
+/**
+ * spi_fc_probe - Configure Flow Control for called slave device.
+ * @spi: spi_device to register.
+ *
+ * Companion function to spi_setup.  Devices which support Flow Control
+ * functionality need to call this function to be able to use it.
+ *
+ * Return: 0 on success; negative errno on failure.
+ */
+int spi_fc_probe(struct spi_device *spi)
+{
+	struct device_node *np = spi->dev.of_node;
+	int ret;
+
+	if (!np)
+		return 0;
+
+	if (!(spi->mode & SPI_FC_MASK) || spi->mode & SPI_FC_HW_ONLY)
+		return 0;
+
+	spi->fc_gpio = devm_gpiod_get(&spi->dev, "fc", GPIOD_IN);
+	if (IS_ERR(spi->fc_gpio)) {
+		ret = PTR_ERR(spi->fc_gpio);
+		dev_err(&spi->dev, "Failed to request FC GPIO: %d\n", ret);
+		return ret;
+	}
+
+	init_completion(&spi->fc_complete);
+
+	spi->fc_irq = gpiod_to_irq(spi->fc_gpio);
+	if (spi->fc_irq < 0) {
+		/*
+		 * This will dramtically affect transfer speed,
+		 * so it is not recommended, but possible use case.
+		 */
+		dev_warn(&spi->dev, "gpio-fc, filed to get irq for configured pin, use slow polling instead\n");
+	} else {
+		snprintf(spi->fc_irq_name, sizeof(spi->fc_irq_name), "spi-fc-%s",
+			 dev_name(&spi->dev));
+		ret = devm_request_irq(&spi->dev, spi->fc_irq, spi_fc_rq,
+				       IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
+				       spi->fc_irq_name, spi);
+		if (ret) {
+			dev_err(&spi->dev, "Failed to request FC IRQ\n");
+			return ret;
+		}
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(spi_fc_probe);
+
+/*-------------------------------------------------------------------------*/
 
 /* SPI devices should normally not be created by SPI device drivers; that
  * would make them board-specific.  Similarly with SPI master drivers.
@@ -687,6 +839,9 @@  int spi_register_board_info(struct spi_board_info const *info, unsigned n)
 
 static void spi_set_cs(struct spi_device *spi, bool enable)
 {
+	spi->cs_enabled = enable;
+	reinit_completion(&spi->fc_complete);
+
 	if (spi->mode & SPI_CS_HIGH)
 		enable = !enable;
 
@@ -941,9 +1096,15 @@  static int spi_transfer_one_message(struct spi_master *master,
 	unsigned long ms = 1;
 	struct spi_statistics *statm = &master->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
+	struct spi_device *spi = msg->spi;
 
 	spi_set_cs(msg->spi, true);
 
+	if (!spi_fc_wait_rq(spi, SPI_FC_READY | SPI_FC_MISO_READY)) {
+		ret = -EREMOTEIO;
+		goto out;
+	}
+
 	SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
 	SPI_STATISTICS_INCREMENT_FIELD(stats, messages);
 
@@ -1006,8 +1167,20 @@  static int spi_transfer_one_message(struct spi_master *master,
 				keep_cs = true;
 			} else {
 				spi_set_cs(msg->spi, false);
-				udelay(10);
+
+				if (!spi_fc_wait_rq(spi, SPI_FC_STOP_ACK)) {
+					ret = -EREMOTEIO;
+					break;
+				}
+
+				if (!(spi->mode & SPI_FC_STOP_ACK))
+					udelay(10);
 				spi_set_cs(msg->spi, true);
+
+				if (!spi_fc_wait_rq(spi, SPI_FC_READY)) {
+					ret = -EREMOTEIO;
+					break;
+				}
 			}
 		}
 
@@ -1015,8 +1188,12 @@  static int spi_transfer_one_message(struct spi_master *master,
 	}
 
 out:
-	if (ret != 0 || !keep_cs)
+
+	if (ret != 0 || !keep_cs) {
 		spi_set_cs(msg->spi, false);
+		if (ret != -EREMOTEIO && !spi_fc_wait_rq(spi, SPI_FC_STOP_ACK))
+			ret = -EREMOTEIO;
+	}
 
 	if (msg->status == -EINPROGRESS)
 		msg->status = ret;
@@ -1483,6 +1660,16 @@  of_register_spi_device(struct spi_master *master, struct device_node *nc)
 		spi->mode |= SPI_3WIRE;
 	if (of_find_property(nc, "spi-lsb-first", NULL))
 		spi->mode |= SPI_LSB_FIRST;
+	if (of_find_property(nc, "spi-fc-ready", NULL))
+		spi->mode |= SPI_FC_READY;
+	if (of_find_property(nc, "spi-fc-stop-ack", NULL))
+		spi->mode |= SPI_FC_STOP_ACK;
+	if (of_find_property(nc, "spi-fc-pause", NULL))
+		spi->mode |= SPI_FC_PAUSE;
+	if (of_find_property(nc, "spi-fc-request", NULL))
+		spi->mode |= SPI_FC_REQUEST;
+	if (of_find_property(nc, "spi-fc-miso-ready", NULL))
+		spi->mode |= SPI_FC_MISO_READY;
 
 	/* Device DUAL/QUAD mode */
 	if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 53be3a4..07803f8 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -136,7 +136,7 @@  struct spi_device {
 	u32			max_speed_hz;
 	u8			chip_select;
 	u8			bits_per_word;
-	u16			mode;
+	u32			mode;
 #define	SPI_CPHA	0x01			/* clock phase */
 #define	SPI_CPOL	0x02			/* clock polarity */
 #define	SPI_MODE_0	(0|0)			/* (original MicroWire) */
@@ -148,16 +148,65 @@  struct spi_device {
 #define	SPI_3WIRE	0x10			/* SI/SO signals shared */
 #define	SPI_LOOP	0x20			/* loopback mode */
 #define	SPI_NO_CS	0x40			/* 1 dev/bus, no chipselect */
-#define	SPI_READY	0x80			/* slave pulls low to pause */
+/*
+ * Flow control: Ready Sequence (SPI_FC_READY)
+ * Master CS   |-----1\_______________________|
+ * Slave  FC   |--------2\____________________|
+ * DATA        |-----------3\_________________|
+ * 1. Chips Select set to active by Master.
+ * 2. Flow Control set to active by Slave.
+ * 3. Master starting Data transmission.
+ */
+#define	SPI_FC_READY	0x80
 #define	SPI_TX_DUAL	0x100			/* transmit with 2 wires */
 #define	SPI_TX_QUAD	0x200			/* transmit with 4 wires */
 #define	SPI_RX_DUAL	0x400			/* receive with 2 wires */
 #define	SPI_RX_QUAD	0x800			/* receive with 4 wires */
+/*
+ * Flow control: Pause (SPI_FC_PAUSE)
+ * Master CS   |_______________________/------|
+ * Slave  FC   |_______1/-----\3______/-------|
+ * DATA        |________2/------\4_____/------|
+ */
+#define SPI_FC_PAUSE		0x1000
+/*
+ * Flow control: ACK End of Data (SPI_FC_STOP_ACK)
+ * Master CS   |______________________/2------|
+ * Slave  FC   |________________________/3----|
+ * DATA        |__________________/1----------|
+ */
+#define SPI_FC_STOP_ACK		0x2000
+/*
+ * Flow control: Request Sequence (SPI_FC_REQUEST)
+ * Master CS   |-------2\_____________________|
+ * Slave  FC   |-----1\_______________________|
+ * DATA        |-----------3\_________________|
+ */
+#define SPI_FC_REQUEST		0x4000
+/* If complete FC is done by HW or controller driver, set this flag */
+#define SPI_FC_HW_ONLY		0x8000
+/*
+ * Flow control: Ready signal on MISO (SPI_FC_MISO_READY)
+ * Master CS   |-----1\_______________________|
+ * MISO/DATA   |------2\____3/----------------|
+ * CONV START  |       ^                      |
+ * DATA READY  |             ^                |
+ * When CS get asserted (1), MISO/DATA becomes dominant low (2)
+ * and the ADC conversion starts (within 100ns of (1)).
+ * When MISO/DATA goes dominant high (3) then the conversion has finished
+ * and the transfer may start.
+ * Example: MAX187/189 SPI-ADC.
+ */
+#define SPI_FC_MISO_READY	0x10000
+#define SPI_FC_MASK	(SPI_FC_READY | SPI_FC_PAUSE | \
+			 SPI_FC_STOP_ACK | SPI_FC_REQUEST)
+
 	int			irq;
 	void			*controller_state;
 	void			*controller_data;
 	char			modalias[SPI_NAME_SIZE];
 	int			cs_gpio;	/* chip select gpio */
+	int			cs_enabled;
 
 	/* the statistics */
 	struct spi_statistics	statistics;
@@ -171,6 +220,13 @@  struct spi_device {
 	 *  - chipselect delays
 	 *  - ...
 	 */
+
+	void (*request_cb)(struct spi_device *spi);
+	atomic_t		active_rq;
+	struct completion	fc_complete;
+	struct gpio_desc	*fc_gpio;	/* flow control */
+	int			fc_irq;
+	char			fc_irq_name[32];
 };
 
 static inline struct spi_device *to_spi_device(struct device *dev)
@@ -282,7 +338,6 @@  static inline void spi_unregister_driver(struct spi_driver *sdrv)
 #define module_spi_driver(__spi_driver) \
 	module_driver(__spi_driver, spi_register_driver, \
 			spi_unregister_driver)
-
 /**
  * struct spi_master - interface to SPI master controller
  * @dev: device interface to this driver
@@ -537,6 +592,10 @@  struct spi_master {
 	/* dummy data for full duplex devices */
 	void			*dummy_rx;
 	void			*dummy_tx;
+
+	int	(*wait_for_rq)(struct spi_device *spi);
+	/* some devices use MISO for flow control, see SPI_FC_MISO_READY */
+	int	(*get_miso_level)(struct spi_device *spi);
 };
 
 static inline void *spi_master_get_devdata(struct spi_master *master)
@@ -1146,4 +1205,7 @@  spi_transfer_is_last(struct spi_master *master, struct spi_transfer *xfer)
 	return list_is_last(&xfer->transfer_list, &master->cur_msg->transfers);
 }
 
+int spi_fc_wait_rq(struct spi_device *spi, u32 s5w_state);
+int spi_fc_probe(struct spi_device *spi);
+
 #endif /* __LINUX_SPI_H */