[v5,2/6] cxl/acpi: Introduce cxl_root, the root of a cxl_port topology

Commit Message

Dan Williams June 6, 2021, 6:05 a.m. UTC

While CXL builds upon the PCI software model for enumeration and
endpoint control, a static platform component is required to bootstrap
the CXL memory layout. Similar to how ACPI identifies root-level PCI
memory resources the ACPI identifies the address space and interleave
configuration for CXL Memory.

In addition to identifying the host bridges, ACPI is responsible for
enumerating the CXL memory space that can be addressed by downstream
decoders. This is similar to the requirement for ACPI to publish
resources reported by _CRS for PCI host bridges. Specifically ACPI
publishes a table, CXL Early Discovery Table (CEDT), which includes a
list of CXL Memory resource, CXL Fixed Memory Window Structures (CFMWS).

For now introduce the core infrastructure for a cxl_port hierarchy
starting with a root level anchor represented by the ACPI0017 device.

Follow on changes model support for the configurable decode capabilities
of cxl_port instances.

Co-developed-by: Alison Schofield <[e-mail]>
Signed-off-by: Alison Schofield <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>
---
 Documentation/ABI/testing/sysfs-bus-cxl |   11 ++
 drivers/cxl/Kconfig                     |   15 +++
 drivers/cxl/Makefile                    |    2 
 drivers/cxl/acpi.c                      |   39 ++++++++
 drivers/cxl/core.c                      |  160 +++++++++++++++++++++++++++++++
 drivers/cxl/cxl.h                       |   23 ++++
 6 files changed, 250 insertions(+)
 create mode 100644 drivers/cxl/acpi.c

Comments

Rafael J. Wysocki June 7, 2021, 12:27 p.m. UTC | #1

On Sun, Jun 6, 2021 at 8:05 AM Dan Williams <[e-mail]> wrote:
>
> While CXL builds upon the PCI software model for enumeration and
> endpoint control, a static platform component is required to bootstrap
> the CXL memory layout. Similar to how ACPI identifies root-level PCI
> memory resources the ACPI identifies the address space and interleave
> configuration for CXL Memory.
>
> In addition to identifying the host bridges, ACPI is responsible for
> enumerating the CXL memory space that can be addressed by downstream
> decoders. This is similar to the requirement for ACPI to publish
> resources reported by _CRS for PCI host bridges. Specifically ACPI
> publishes a table, CXL Early Discovery Table (CEDT), which includes a
> list of CXL Memory resource, CXL Fixed Memory Window Structures (CFMWS).
>
> For now introduce the core infrastructure for a cxl_port hierarchy
> starting with a root level anchor represented by the ACPI0017 device.
>
> Follow on changes model support for the configurable decode capabilities
> of cxl_port instances.
>
> Co-developed-by: Alison Schofield <[e-mail]>
> Signed-off-by: Alison Schofield <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>

From the ACPI perspective:

Acked-by: Rafael J. Wysocki <[e-mail]>

> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |   11 ++
>  drivers/cxl/Kconfig                     |   15 +++
>  drivers/cxl/Makefile                    |    2
>  drivers/cxl/acpi.c                      |   39 ++++++++
>  drivers/cxl/core.c                      |  160 +++++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h                       |   23 ++++
>  6 files changed, 250 insertions(+)
>  create mode 100644 drivers/cxl/acpi.c
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 2fe7490ad6a8..fb996ced7629 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -24,3 +24,14 @@ Description:
>                 (RO) "Persistent Only Capacity" as bytes. Represents the
>                 identically named field in the Identify Memory Device Output
>                 Payload in the CXL-2.0 specification.
> +
> +What:          /sys/bus/cxl/devices/portX/uport
> +Date:          May, 2021
> +KernelVersion: v5.14
> +Contact:       [e-mail]
> +Description:
> +               CXL port objects are enumerated from either a platform firmware
> +               device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
> +               CXL component registers. The 'uport' symlink connects the CXL
> +               portX object to the device that published the CXL port
> +               capability.
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 5483ba92b6da..d2573f6aef91 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -45,4 +45,19 @@ config CXL_MEM_RAW_COMMANDS
>           potential impact to memory currently in use by the kernel.
>
>           If developing CXL hardware or the driver say Y, otherwise say N.
> +
> +config CXL_ACPI
> +       tristate "CXL ACPI: Platform Support"
> +       depends on ACPI
> +       help
> +         Enable support for host managed device memory (HDM) resources
> +         published by a platform's ACPI CXL memory layout description.  See
> +         Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
> +         specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
> +         (https://www.computeexpresslink.org/spec-landing). The CXL core
> +         consumes these resource to publish the root of a cxl_port decode
> +         hierarchy to map regions that represent System RAM, or Persistent
> +         Memory regions to be managed by LIBNVDIMM.
> +
> +         If unsure say 'm'.
>  endif
> diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> index d9d282dc15be..a29efb3e8ad2 100644
> --- a/drivers/cxl/Makefile
> +++ b/drivers/cxl/Makefile
> @@ -1,7 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_CXL_BUS) += cxl_core.o
>  obj-$(CONFIG_CXL_MEM) += cxl_pci.o
> +obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
>
>  ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
>  cxl_core-y := core.o
>  cxl_pci-y := pci.o
> +cxl_acpi-y := acpi.o
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> new file mode 100644
> index 000000000000..556d25ab6966
> --- /dev/null
> +++ b/drivers/cxl/acpi.c
> @@ -0,0 +1,39 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/acpi.h>
> +#include "cxl.h"
> +
> +static int cxl_acpi_probe(struct platform_device *pdev)
> +{
> +       struct cxl_port *root_port;
> +       struct device *host = &pdev->dev;
> +
> +       root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
> +       if (IS_ERR(root_port))
> +               return PTR_ERR(root_port);
> +       dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
> +
> +       return 0;
> +}
> +
> +static const struct acpi_device_id cxl_acpi_ids[] = {
> +       { "ACPI0017", 0 },
> +       { "", 0 },
> +};
> +MODULE_DEVICE_TABLE(acpi, cxl_acpi_ids);
> +
> +static struct platform_driver cxl_acpi_driver = {
> +       .probe = cxl_acpi_probe,
> +       .driver = {
> +               .name = KBUILD_MODNAME,
> +               .acpi_match_table = cxl_acpi_ids,
> +       },
> +};
> +
> +module_platform_driver(cxl_acpi_driver);
> +MODULE_LICENSE("GPL v2");
> +MODULE_IMPORT_NS(CXL);
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index 853666d8a9f5..dbbb34618d7d 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -4,6 +4,8 @@
>  #include <linux/device.h>
>  #include <linux/module.h>
>  #include <linux/pci.h>
> +#include <linux/slab.h>
> +#include <linux/idr.h>
>  #include "cxl.h"
>
>  /**
> @@ -13,6 +15,164 @@
>   * point for cross-device interleave coordination through cxl ports.
>   */
>
> +static DEFINE_IDA(cxl_port_ida);
> +
> +static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
> +                           char *buf)
> +{
> +       return sysfs_emit(buf, "%s\n", dev->type->name);
> +}
> +static DEVICE_ATTR_RO(devtype);
> +
> +static struct attribute *cxl_base_attributes[] = {
> +       &dev_attr_devtype.attr,
> +       NULL,
> +};
> +
> +static struct attribute_group cxl_base_attribute_group = {
> +       .attrs = cxl_base_attributes,
> +};
> +
> +static void cxl_port_release(struct device *dev)
> +{
> +       struct cxl_port *port = to_cxl_port(dev);
> +
> +       ida_free(&cxl_port_ida, port->id);
> +       kfree(port);
> +}
> +
> +static const struct attribute_group *cxl_port_attribute_groups[] = {
> +       &cxl_base_attribute_group,
> +       NULL,
> +};
> +
> +static const struct device_type cxl_port_type = {
> +       .name = "cxl_port",
> +       .release = cxl_port_release,
> +       .groups = cxl_port_attribute_groups,
> +};
> +
> +struct cxl_port *to_cxl_port(struct device *dev)
> +{
> +       if (dev_WARN_ONCE(dev, dev->type != &cxl_port_type,
> +                         "not a cxl_port device\n"))
> +               return NULL;
> +       return container_of(dev, struct cxl_port, dev);
> +}
> +
> +static void unregister_dev(void *dev)
> +{
> +       device_unregister(dev);
> +}
> +
> +static void cxl_unlink_uport(void *_port)
> +{
> +       struct cxl_port *port = _port;
> +
> +       sysfs_remove_link(&port->dev.kobj, "uport");
> +}
> +
> +static int devm_cxl_link_uport(struct device *host, struct cxl_port *port)
> +{
> +       int rc;
> +
> +       rc = sysfs_create_link(&port->dev.kobj, &port->uport->kobj, "uport");
> +       if (rc)
> +               return rc;
> +       return devm_add_action_or_reset(host, cxl_unlink_uport, port);
> +}
> +
> +static struct cxl_port *cxl_port_alloc(struct device *uport,
> +                                      resource_size_t component_reg_phys,
> +                                      struct cxl_port *parent_port)
> +{
> +       struct cxl_port *port;
> +       struct device *dev;
> +       int rc;
> +
> +       port = kzalloc(sizeof(*port), GFP_KERNEL);
> +       if (!port)
> +               return ERR_PTR(-ENOMEM);
> +
> +       rc = ida_alloc(&cxl_port_ida, GFP_KERNEL);
> +       if (rc < 0)
> +               goto err;
> +       port->id = rc;
> +
> +       /*
> +        * The top-level cxl_port "cxl_root" does not have a cxl_port as
> +        * its parent and it does not have any corresponding component
> +        * registers as its decode is described by a fixed platform
> +        * description.
> +        */
> +       dev = &port->dev;
> +       if (parent_port)
> +               dev->parent = &parent_port->dev;
> +       else
> +               dev->parent = uport;
> +
> +       port->uport = uport;
> +       port->component_reg_phys = component_reg_phys;
> +
> +       device_initialize(dev);
> +       device_set_pm_not_required(dev);
> +       dev->bus = &cxl_bus_type;
> +       dev->type = &cxl_port_type;
> +
> +       return port;
> +
> +err:
> +       kfree(port);
> +       return ERR_PTR(rc);
> +}
> +
> +/**
> + * devm_cxl_add_port - register a cxl_port in CXL memory decode hierarchy
> + * @host: host device for devm operations
> + * @uport: "physical" device implementing this upstream port
> + * @component_reg_phys: (optional) for configurable cxl_port instances
> + * @parent_port: next hop up in the CXL memory decode hierarchy
> + */
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +                                  resource_size_t component_reg_phys,
> +                                  struct cxl_port *parent_port)
> +{
> +       struct cxl_port *port;
> +       struct device *dev;
> +       int rc;
> +
> +       port = cxl_port_alloc(uport, component_reg_phys, parent_port);
> +       if (IS_ERR(port))
> +               return port;
> +
> +       dev = &port->dev;
> +       if (parent_port)
> +               rc = dev_set_name(dev, "port%d", port->id);
> +       else
> +               rc = dev_set_name(dev, "root%d", port->id);
> +       if (rc)
> +               goto err;
> +
> +       rc = device_add(dev);
> +       if (rc)
> +               goto err;
> +
> +       rc = devm_add_action_or_reset(host, unregister_dev, dev);
> +       if (rc)
> +               return ERR_PTR(rc);
> +
> +       rc = devm_cxl_link_uport(host, port);
> +       if (rc)
> +               return ERR_PTR(rc);
> +
> +       return port;
> +
> +err:
> +       put_device(dev);
> +       return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_GPL(devm_cxl_add_port);
> +
>  /**
>   * cxl_probe_component_regs() - Detect CXL Component register blocks
>   * @dev: Host device of the @base mapping
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 2c47e9cffd44..46c81165c210 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -145,5 +145,28 @@ int cxl_map_device_regs(struct pci_dev *pdev,
>                         struct cxl_device_regs *regs,
>                         struct cxl_register_map *map);
>
> +#define CXL_RESOURCE_NONE ((resource_size_t) -1)
> +
> +/**
> + * struct cxl_port - logical collection of upstream port devices and
> + *                  downstream port devices to construct a CXL memory
> + *                  decode hierarchy.
> + * @dev: this port's device
> + * @uport: PCI or platform device implementing the upstream port capability
> + * @id: id for port device-name
> + * @component_regs_phys: component register capability base address (optional)
> + */
> +struct cxl_port {
> +       struct device dev;
> +       struct device *uport;
> +       int id;
> +       resource_size_t component_reg_phys;
> +};
> +
> +struct cxl_port *to_cxl_port(struct device *dev);
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +                                  resource_size_t component_reg_phys,
> +                                  struct cxl_port *parent_port);
> +
>  extern struct bus_type cxl_bus_type;
>  #endif /* __CXL_H__ */
>

Ben Widawsky June 7, 2021, 10:18 p.m. UTC | #2

On 21-06-05 23:05:04, Dan Williams wrote:
> While CXL builds upon the PCI software model for enumeration and
> endpoint control, a static platform component is required to bootstrap
> the CXL memory layout. Similar to how ACPI identifies root-level PCI
> memory resources the ACPI identifies the address space and interleave
> configuration for CXL Memory.
> 
> In addition to identifying the host bridges, ACPI is responsible for
> enumerating the CXL memory space that can be addressed by downstream
> decoders. This is similar to the requirement for ACPI to publish
> resources reported by _CRS for PCI host bridges. Specifically ACPI
> publishes a table, CXL Early Discovery Table (CEDT), which includes a
> list of CXL Memory resource, CXL Fixed Memory Window Structures (CFMWS).
> 
> For now introduce the core infrastructure for a cxl_port hierarchy
> starting with a root level anchor represented by the ACPI0017 device.
> 
> Follow on changes model support for the configurable decode capabilities
> of cxl_port instances.
> 
> Co-developed-by: Alison Schofield <[e-mail]>
> Signed-off-by: Alison Schofield <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |   11 ++
>  drivers/cxl/Kconfig                     |   15 +++
>  drivers/cxl/Makefile                    |    2 
>  drivers/cxl/acpi.c                      |   39 ++++++++
>  drivers/cxl/core.c                      |  160 +++++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h                       |   23 ++++
>  6 files changed, 250 insertions(+)
>  create mode 100644 drivers/cxl/acpi.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 2fe7490ad6a8..fb996ced7629 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -24,3 +24,14 @@ Description:
>  		(RO) "Persistent Only Capacity" as bytes. Represents the
>  		identically named field in the Identify Memory Device Output
>  		Payload in the CXL-2.0 specification.
> +
> +What:		/sys/bus/cxl/devices/portX/uport
> +Date:		May, 2021
> +KernelVersion:	v5.14
> +Contact:	[e-mail]
> +Description:
> +		CXL port objects are enumerated from either a platform firmware
> +		device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
> +		CXL component registers. The 'uport' symlink connects the CXL
> +		portX object to the device that published the CXL port
> +		capability.
> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 5483ba92b6da..d2573f6aef91 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -45,4 +45,19 @@ config CXL_MEM_RAW_COMMANDS
>  	  potential impact to memory currently in use by the kernel.
>  
>  	  If developing CXL hardware or the driver say Y, otherwise say N.
> +
> +config CXL_ACPI
> +	tristate "CXL ACPI: Platform Support"
> +	depends on ACPI
> +	help
> +	  Enable support for host managed device memory (HDM) resources
> +	  published by a platform's ACPI CXL memory layout description.  See
> +	  Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
> +	  specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
> +	  (https://www.computeexpresslink.org/spec-landing). The CXL core
> +	  consumes these resource to publish the root of a cxl_port decode
> +	  hierarchy to map regions that represent System RAM, or Persistent
> +	  Memory regions to be managed by LIBNVDIMM.
> +
> +	  If unsure say 'm'.
>  endif
> diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> index d9d282dc15be..a29efb3e8ad2 100644
> --- a/drivers/cxl/Makefile
> +++ b/drivers/cxl/Makefile
> @@ -1,7 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_CXL_BUS) += cxl_core.o
>  obj-$(CONFIG_CXL_MEM) += cxl_pci.o
> +obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
>  
>  ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
>  cxl_core-y := core.o
>  cxl_pci-y := pci.o
> +cxl_acpi-y := acpi.o
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> new file mode 100644
> index 000000000000..556d25ab6966
> --- /dev/null
> +++ b/drivers/cxl/acpi.c
> @@ -0,0 +1,39 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/acpi.h>
> +#include "cxl.h"
> +
> +static int cxl_acpi_probe(struct platform_device *pdev)
> +{
> +	struct cxl_port *root_port;
> +	struct device *host = &pdev->dev;
> +
> +	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
> +	if (IS_ERR(root_port))
> +		return PTR_ERR(root_port);
> +	dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
> +
> +	return 0;
> +}
> +
> +static const struct acpi_device_id cxl_acpi_ids[] = {
> +	{ "ACPI0017", 0 },
> +	{ "", 0 },
> +};
> +MODULE_DEVICE_TABLE(acpi, cxl_acpi_ids);
> +
> +static struct platform_driver cxl_acpi_driver = {
> +	.probe = cxl_acpi_probe,
> +	.driver = {
> +		.name = KBUILD_MODNAME,
> +		.acpi_match_table = cxl_acpi_ids,
> +	},
> +};
> +
> +module_platform_driver(cxl_acpi_driver);
> +MODULE_LICENSE("GPL v2");
> +MODULE_IMPORT_NS(CXL);
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index 853666d8a9f5..dbbb34618d7d 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -4,6 +4,8 @@
>  #include <linux/device.h>
>  #include <linux/module.h>
>  #include <linux/pci.h>
> +#include <linux/slab.h>
> +#include <linux/idr.h>
>  #include "cxl.h"
>  
>  /**
> @@ -13,6 +15,164 @@
>   * point for cross-device interleave coordination through cxl ports.
>   */
>  
> +static DEFINE_IDA(cxl_port_ida);
> +
> +static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
> +			    char *buf)
> +{
> +	return sysfs_emit(buf, "%s\n", dev->type->name);
> +}
> +static DEVICE_ATTR_RO(devtype);
> +
> +static struct attribute *cxl_base_attributes[] = {
> +	&dev_attr_devtype.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group cxl_base_attribute_group = {
> +	.attrs = cxl_base_attributes,
> +};
> +
> +static void cxl_port_release(struct device *dev)
> +{
> +	struct cxl_port *port = to_cxl_port(dev);
> +
> +	ida_free(&cxl_port_ida, port->id);
> +	kfree(port);
> +}
> +
> +static const struct attribute_group *cxl_port_attribute_groups[] = {
> +	&cxl_base_attribute_group,
> +	NULL,
> +};
> +
> +static const struct device_type cxl_port_type = {
> +	.name = "cxl_port",
> +	.release = cxl_port_release,
> +	.groups = cxl_port_attribute_groups,
> +};
> +
> +struct cxl_port *to_cxl_port(struct device *dev)
> +{
> +	if (dev_WARN_ONCE(dev, dev->type != &cxl_port_type,
> +			  "not a cxl_port device\n"))
> +		return NULL;
> +	return container_of(dev, struct cxl_port, dev);
> +}
> +
> +static void unregister_dev(void *dev)
> +{
> +	device_unregister(dev);
> +}
> +
> +static void cxl_unlink_uport(void *_port)
> +{
> +	struct cxl_port *port = _port;
> +
> +	sysfs_remove_link(&port->dev.kobj, "uport");
> +}
> +
> +static int devm_cxl_link_uport(struct device *host, struct cxl_port *port)
> +{
> +	int rc;
> +
> +	rc = sysfs_create_link(&port->dev.kobj, &port->uport->kobj, "uport");
> +	if (rc)
> +		return rc;
> +	return devm_add_action_or_reset(host, cxl_unlink_uport, port);
> +}
> +
> +static struct cxl_port *cxl_port_alloc(struct device *uport,
> +				       resource_size_t component_reg_phys,
> +				       struct cxl_port *parent_port)
> +{
> +	struct cxl_port *port;
> +	struct device *dev;
> +	int rc;
> +
> +	port = kzalloc(sizeof(*port), GFP_KERNEL);
> +	if (!port)
> +		return ERR_PTR(-ENOMEM);
> +
> +	rc = ida_alloc(&cxl_port_ida, GFP_KERNEL);
> +	if (rc < 0)
> +		goto err;
> +	port->id = rc;
> +
> +	/*
> +	 * The top-level cxl_port "cxl_root" does not have a cxl_port as
> +	 * its parent and it does not have any corresponding component
> +	 * registers as its decode is described by a fixed platform
> +	 * description.
> +	 */
> +	dev = &port->dev;
> +	if (parent_port)
> +		dev->parent = &parent_port->dev;
> +	else
> +		dev->parent = uport;
> +
> +	port->uport = uport;
> +	port->component_reg_phys = component_reg_phys;
> +
> +	device_initialize(dev);
> +	device_set_pm_not_required(dev);
> +	dev->bus = &cxl_bus_type;
> +	dev->type = &cxl_port_type;
> +
> +	return port;
> +
> +err:
> +	kfree(port);
> +	return ERR_PTR(rc);
> +}
> +
> +/**
> + * devm_cxl_add_port - register a cxl_port in CXL memory decode hierarchy
> + * @host: host device for devm operations
> + * @uport: "physical" device implementing this upstream port
> + * @component_reg_phys: (optional) for configurable cxl_port instances
> + * @parent_port: next hop up in the CXL memory decode hierarchy
> + */
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +				   resource_size_t component_reg_phys,
> +				   struct cxl_port *parent_port)
> +{
> +	struct cxl_port *port;
> +	struct device *dev;
> +	int rc;
> +
> +	port = cxl_port_alloc(uport, component_reg_phys, parent_port);
> +	if (IS_ERR(port))
> +		return port;
> +
> +	dev = &port->dev;
> +	if (parent_port)
> +		rc = dev_set_name(dev, "port%d", port->id);
> +	else
> +		rc = dev_set_name(dev, "root%d", port->id);
> +	if (rc)
> +		goto err;
> +
> +	rc = device_add(dev);
> +	if (rc)
> +		goto err;
> +
> +	rc = devm_add_action_or_reset(host, unregister_dev, dev);
> +	if (rc)
> +		return ERR_PTR(rc);
> +
> +	rc = devm_cxl_link_uport(host, port);
> +	if (rc)
> +		return ERR_PTR(rc);
> +
> +	return port;
> +
> +err:
> +	put_device(dev);
> +	return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_GPL(devm_cxl_add_port);
> +
>  /**
>   * cxl_probe_component_regs() - Detect CXL Component register blocks
>   * @dev: Host device of the @base mapping
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 2c47e9cffd44..46c81165c210 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -145,5 +145,28 @@ int cxl_map_device_regs(struct pci_dev *pdev,
>  			struct cxl_device_regs *regs,
>  			struct cxl_register_map *map);
>  
> +#define CXL_RESOURCE_NONE ((resource_size_t) -1)
> +
> +/**
> + * struct cxl_port - logical collection of upstream port devices and
> + *		     downstream port devices to construct a CXL memory
> + *		     decode hierarchy.
> + * @dev: this port's device
> + * @uport: PCI or platform device implementing the upstream port capability
> + * @id: id for port device-name
> + * @component_regs_phys: component register capability base address (optional)
> + */
> +struct cxl_port {
> +	struct device dev;
> +	struct device *uport;
> +	int id;
> +	resource_size_t component_reg_phys;
> +};
> +

I think the new kernel doc info needs to be added in the
Documentation/driver-api/cxl/ somewhere. We haven't yet told sphinx about this
file.

> +struct cxl_port *to_cxl_port(struct device *dev);
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +				   resource_size_t component_reg_phys,
> +				   struct cxl_port *parent_port);
> +
>  extern struct bus_type cxl_bus_type;
>  #endif /* __CXL_H__ */
>

Jonathan Cameron June 8, 2021, 11:28 a.m. UTC | #3

On Sat, 5 Jun 2021 23:05:04 -0700
Dan Williams <[e-mail]> wrote:

> While CXL builds upon the PCI software model for enumeration and
> endpoint control, a static platform component is required to bootstrap
> the CXL memory layout. Similar to how ACPI identifies root-level PCI
> memory resources the ACPI identifies the address space and interleave
> configuration for CXL Memory.
> 
> In addition to identifying the host bridges, ACPI is responsible for
> enumerating the CXL memory space that can be addressed by downstream
> decoders. This is similar to the requirement for ACPI to publish
> resources reported by _CRS for PCI host bridges. Specifically ACPI
> publishes a table, CXL Early Discovery Table (CEDT), which includes a
> list of CXL Memory resource, CXL Fixed Memory Window Structures (CFMWS).
> 
> For now introduce the core infrastructure for a cxl_port hierarchy
> starting with a root level anchor represented by the ACPI0017 device.
> 
> Follow on changes model support for the configurable decode capabilities
> of cxl_port instances.
> 
> Co-developed-by: Alison Schofield <[e-mail]>
> Signed-off-by: Alison Schofield <[e-mail]>
> Signed-off-by: Dan Williams <[e-mail]>

Two trivial comments inline.

Reviewed-by: Jonathan Cameron <[e-mail]>

> ---
>  Documentation/ABI/testing/sysfs-bus-cxl |   11 ++
>  drivers/cxl/Kconfig                     |   15 +++
>  drivers/cxl/Makefile                    |    2 
>  drivers/cxl/acpi.c                      |   39 ++++++++
>  drivers/cxl/core.c                      |  160 +++++++++++++++++++++++++++++++
>  drivers/cxl/cxl.h                       |   23 ++++
>  6 files changed, 250 insertions(+)
>  create mode 100644 drivers/cxl/acpi.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 2fe7490ad6a8..fb996ced7629 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -24,3 +24,14 @@ Description:
>  		(RO) "Persistent Only Capacity" as bytes. Represents the
>  		identically named field in the Identify Memory Device Output
>  		Payload in the CXL-2.0 specification.
> +
> +What:		/sys/bus/cxl/devices/portX/uport
> +Date:		May, 2021
> +KernelVersion:	v5.14
> +Contact:	[e-mail]
> +Description:
> +		CXL port objects are enumerated from either a platform firmware
> +		device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
> +		CXL component registers. The 'uport' symlink connects the CXL
> +		portX object to the device that published the CXL port
> +		capability.

Is this a complete list of ABI added? Looks like we also add devtype
attribute in this series.

Mind you I just realized I didn't document the proposed CDAT file either yet.


> diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> index 5483ba92b6da..d2573f6aef91 100644
> --- a/drivers/cxl/Kconfig
> +++ b/drivers/cxl/Kconfig
> @@ -45,4 +45,19 @@ config CXL_MEM_RAW_COMMANDS
>  	  potential impact to memory currently in use by the kernel.
>  
>  	  If developing CXL hardware or the driver say Y, otherwise say N.
> +
> +config CXL_ACPI
> +	tristate "CXL ACPI: Platform Support"
> +	depends on ACPI
> +	help
> +	  Enable support for host managed device memory (HDM) resources
> +	  published by a platform's ACPI CXL memory layout description.  See
> +	  Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
> +	  specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
> +	  (https://www.computeexpresslink.org/spec-landing). The CXL core
> +	  consumes these resource to publish the root of a cxl_port decode
> +	  hierarchy to map regions that represent System RAM, or Persistent
> +	  Memory regions to be managed by LIBNVDIMM.
> +
> +	  If unsure say 'm'.
>  endif
> diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> index d9d282dc15be..a29efb3e8ad2 100644
> --- a/drivers/cxl/Makefile
> +++ b/drivers/cxl/Makefile
> @@ -1,7 +1,9 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_CXL_BUS) += cxl_core.o
>  obj-$(CONFIG_CXL_MEM) += cxl_pci.o
> +obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
>  
>  ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
>  cxl_core-y := core.o
>  cxl_pci-y := pci.o
> +cxl_acpi-y := acpi.o
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> new file mode 100644
> index 000000000000..556d25ab6966
> --- /dev/null
> +++ b/drivers/cxl/acpi.c
> @@ -0,0 +1,39 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/acpi.h>
> +#include "cxl.h"
> +
> +static int cxl_acpi_probe(struct platform_device *pdev)
> +{
> +	struct cxl_port *root_port;
> +	struct device *host = &pdev->dev;
> +
> +	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
> +	if (IS_ERR(root_port))
> +		return PTR_ERR(root_port);
> +	dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
> +
> +	return 0;
> +}
> +
> +static const struct acpi_device_id cxl_acpi_ids[] = {
> +	{ "ACPI0017", 0 },
> +	{ "", 0 },
> +};
> +MODULE_DEVICE_TABLE(acpi, cxl_acpi_ids);
> +
> +static struct platform_driver cxl_acpi_driver = {
> +	.probe = cxl_acpi_probe,
> +	.driver = {
> +		.name = KBUILD_MODNAME,
> +		.acpi_match_table = cxl_acpi_ids,
> +	},
> +};
> +
> +module_platform_driver(cxl_acpi_driver);
> +MODULE_LICENSE("GPL v2");
> +MODULE_IMPORT_NS(CXL);
> diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> index 853666d8a9f5..dbbb34618d7d 100644
> --- a/drivers/cxl/core.c
> +++ b/drivers/cxl/core.c
> @@ -4,6 +4,8 @@
>  #include <linux/device.h>
>  #include <linux/module.h>
>  #include <linux/pci.h>
> +#include <linux/slab.h>
> +#include <linux/idr.h>
>  #include "cxl.h"
>  
>  /**
> @@ -13,6 +15,164 @@
>   * point for cross-device interleave coordination through cxl ports.
>   */
>  
> +static DEFINE_IDA(cxl_port_ida);
> +
> +static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
> +			    char *buf)
> +{
> +	return sysfs_emit(buf, "%s\n", dev->type->name);

I guess it's really small so doesn't matter that much, but not so nice
that we are gaining multiple instances of this same function.

> +}
> +static DEVICE_ATTR_RO(devtype);
> +
> +static struct attribute *cxl_base_attributes[] = {
> +	&dev_attr_devtype.attr,
> +	NULL,
> +};
> +
> +static struct attribute_group cxl_base_attribute_group = {
> +	.attrs = cxl_base_attributes,
> +};
> +
> +static void cxl_port_release(struct device *dev)
> +{
> +	struct cxl_port *port = to_cxl_port(dev);
> +
> +	ida_free(&cxl_port_ida, port->id);
> +	kfree(port);
> +}
> +
> +static const struct attribute_group *cxl_port_attribute_groups[] = {
> +	&cxl_base_attribute_group,
> +	NULL,
> +};
> +
> +static const struct device_type cxl_port_type = {
> +	.name = "cxl_port",
> +	.release = cxl_port_release,
> +	.groups = cxl_port_attribute_groups,
> +};
> +
> +struct cxl_port *to_cxl_port(struct device *dev)
> +{
> +	if (dev_WARN_ONCE(dev, dev->type != &cxl_port_type,
> +			  "not a cxl_port device\n"))
> +		return NULL;
> +	return container_of(dev, struct cxl_port, dev);
> +}
> +
> +static void unregister_dev(void *dev)
> +{
> +	device_unregister(dev);
> +}
> +
> +static void cxl_unlink_uport(void *_port)
> +{
> +	struct cxl_port *port = _port;
> +
> +	sysfs_remove_link(&port->dev.kobj, "uport");
> +}
> +
> +static int devm_cxl_link_uport(struct device *host, struct cxl_port *port)
> +{
> +	int rc;
> +
> +	rc = sysfs_create_link(&port->dev.kobj, &port->uport->kobj, "uport");
> +	if (rc)
> +		return rc;
> +	return devm_add_action_or_reset(host, cxl_unlink_uport, port);
> +}
> +
> +static struct cxl_port *cxl_port_alloc(struct device *uport,
> +				       resource_size_t component_reg_phys,
> +				       struct cxl_port *parent_port)
> +{
> +	struct cxl_port *port;
> +	struct device *dev;
> +	int rc;
> +
> +	port = kzalloc(sizeof(*port), GFP_KERNEL);
> +	if (!port)
> +		return ERR_PTR(-ENOMEM);
> +
> +	rc = ida_alloc(&cxl_port_ida, GFP_KERNEL);
> +	if (rc < 0)
> +		goto err;
> +	port->id = rc;
> +
> +	/*
> +	 * The top-level cxl_port "cxl_root" does not have a cxl_port as
> +	 * its parent and it does not have any corresponding component
> +	 * registers as its decode is described by a fixed platform
> +	 * description.
> +	 */
> +	dev = &port->dev;
> +	if (parent_port)
> +		dev->parent = &parent_port->dev;
> +	else
> +		dev->parent = uport;
> +
> +	port->uport = uport;
> +	port->component_reg_phys = component_reg_phys;
> +
> +	device_initialize(dev);
> +	device_set_pm_not_required(dev);
> +	dev->bus = &cxl_bus_type;
> +	dev->type = &cxl_port_type;
> +
> +	return port;
> +
> +err:
> +	kfree(port);
> +	return ERR_PTR(rc);
> +}
> +
> +/**
> + * devm_cxl_add_port - register a cxl_port in CXL memory decode hierarchy
> + * @host: host device for devm operations
> + * @uport: "physical" device implementing this upstream port
> + * @component_reg_phys: (optional) for configurable cxl_port instances
> + * @parent_port: next hop up in the CXL memory decode hierarchy
> + */
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +				   resource_size_t component_reg_phys,
> +				   struct cxl_port *parent_port)
> +{
> +	struct cxl_port *port;
> +	struct device *dev;
> +	int rc;
> +
> +	port = cxl_port_alloc(uport, component_reg_phys, parent_port);
> +	if (IS_ERR(port))
> +		return port;
> +
> +	dev = &port->dev;
> +	if (parent_port)
> +		rc = dev_set_name(dev, "port%d", port->id);
> +	else
> +		rc = dev_set_name(dev, "root%d", port->id);
> +	if (rc)
> +		goto err;
> +
> +	rc = device_add(dev);
> +	if (rc)
> +		goto err;
> +
> +	rc = devm_add_action_or_reset(host, unregister_dev, dev);
> +	if (rc)
> +		return ERR_PTR(rc);
> +
> +	rc = devm_cxl_link_uport(host, port);
> +	if (rc)
> +		return ERR_PTR(rc);
> +
> +	return port;
> +
> +err:
> +	put_device(dev);
> +	return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_GPL(devm_cxl_add_port);
> +
>  /**
>   * cxl_probe_component_regs() - Detect CXL Component register blocks
>   * @dev: Host device of the @base mapping
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 2c47e9cffd44..46c81165c210 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -145,5 +145,28 @@ int cxl_map_device_regs(struct pci_dev *pdev,
>  			struct cxl_device_regs *regs,
>  			struct cxl_register_map *map);
>  
> +#define CXL_RESOURCE_NONE ((resource_size_t) -1)
> +
> +/**
> + * struct cxl_port - logical collection of upstream port devices and
> + *		     downstream port devices to construct a CXL memory
> + *		     decode hierarchy.
> + * @dev: this port's device
> + * @uport: PCI or platform device implementing the upstream port capability
> + * @id: id for port device-name
> + * @component_regs_phys: component register capability base address (optional)
> + */
> +struct cxl_port {
> +	struct device dev;
> +	struct device *uport;
> +	int id;
> +	resource_size_t component_reg_phys;
> +};
> +
> +struct cxl_port *to_cxl_port(struct device *dev);
> +struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
> +				   resource_size_t component_reg_phys,
> +				   struct cxl_port *parent_port);
> +
>  extern struct bus_type cxl_bus_type;
>  #endif /* __CXL_H__ */
>

Dan Williams June 8, 2021, 8:03 p.m. UTC | #4

On Tue, Jun 8, 2021 at 4:28 AM Jonathan Cameron
<[e-mail]> wrote:
>
> On Sat, 5 Jun 2021 23:05:04 -0700
> Dan Williams <[e-mail]> wrote:
>
> > While CXL builds upon the PCI software model for enumeration and
> > endpoint control, a static platform component is required to bootstrap
> > the CXL memory layout. Similar to how ACPI identifies root-level PCI
> > memory resources the ACPI identifies the address space and interleave
> > configuration for CXL Memory.
> >
> > In addition to identifying the host bridges, ACPI is responsible for
> > enumerating the CXL memory space that can be addressed by downstream
> > decoders. This is similar to the requirement for ACPI to publish
> > resources reported by _CRS for PCI host bridges. Specifically ACPI
> > publishes a table, CXL Early Discovery Table (CEDT), which includes a
> > list of CXL Memory resource, CXL Fixed Memory Window Structures (CFMWS).
> >
> > For now introduce the core infrastructure for a cxl_port hierarchy
> > starting with a root level anchor represented by the ACPI0017 device.
> >
> > Follow on changes model support for the configurable decode capabilities
> > of cxl_port instances.
> >
> > Co-developed-by: Alison Schofield <[e-mail]>
> > Signed-off-by: Alison Schofield <[e-mail]>
> > Signed-off-by: Dan Williams <[e-mail]>
>
> Two trivial comments inline.
>
> Reviewed-by: Jonathan Cameron <[e-mail]>
>

Thanks, as always, for taking a look.

> > ---
> >  Documentation/ABI/testing/sysfs-bus-cxl |   11 ++
> >  drivers/cxl/Kconfig                     |   15 +++
> >  drivers/cxl/Makefile                    |    2
> >  drivers/cxl/acpi.c                      |   39 ++++++++
> >  drivers/cxl/core.c                      |  160 +++++++++++++++++++++++++++++++
> >  drivers/cxl/cxl.h                       |   23 ++++
> >  6 files changed, 250 insertions(+)
> >  create mode 100644 drivers/cxl/acpi.c
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> > index 2fe7490ad6a8..fb996ced7629 100644
> > --- a/Documentation/ABI/testing/sysfs-bus-cxl
> > +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> > @@ -24,3 +24,14 @@ Description:
> >               (RO) "Persistent Only Capacity" as bytes. Represents the
> >               identically named field in the Identify Memory Device Output
> >               Payload in the CXL-2.0 specification.
> > +
> > +What:                /sys/bus/cxl/devices/portX/uport
> > +Date:                May, 2021
> > +KernelVersion:       v5.14
> > +Contact:     [e-mail]
> > +Description:
> > +             CXL port objects are enumerated from either a platform firmware
> > +             device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
> > +             CXL component registers. The 'uport' symlink connects the CXL
> > +             portX object to the device that published the CXL port
> > +             capability.
>
> Is this a complete list of ABI added? Looks like we also add devtype
> attribute in this series.

devtype is the only missing one, I'll add it.

> Mind you I just realized I didn't document the proposed CDAT file either yet.

Hey, we all need prompts to add documentation. I only remembered to
add these here because you commented on it last time.

> > diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> > index 5483ba92b6da..d2573f6aef91 100644
> > --- a/drivers/cxl/Kconfig
> > +++ b/drivers/cxl/Kconfig
> > @@ -45,4 +45,19 @@ config CXL_MEM_RAW_COMMANDS
> >         potential impact to memory currently in use by the kernel.
> >
> >         If developing CXL hardware or the driver say Y, otherwise say N.
> > +
> > +config CXL_ACPI
> > +     tristate "CXL ACPI: Platform Support"
> > +     depends on ACPI
> > +     help
> > +       Enable support for host managed device memory (HDM) resources
> > +       published by a platform's ACPI CXL memory layout description.  See
> > +       Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
> > +       specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
> > +       (https://www.computeexpresslink.org/spec-landing). The CXL core
> > +       consumes these resource to publish the root of a cxl_port decode
> > +       hierarchy to map regions that represent System RAM, or Persistent
> > +       Memory regions to be managed by LIBNVDIMM.
> > +
> > +       If unsure say 'm'.
> >  endif
> > diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
> > index d9d282dc15be..a29efb3e8ad2 100644
> > --- a/drivers/cxl/Makefile
> > +++ b/drivers/cxl/Makefile
> > @@ -1,7 +1,9 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  obj-$(CONFIG_CXL_BUS) += cxl_core.o
> >  obj-$(CONFIG_CXL_MEM) += cxl_pci.o
> > +obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
> >
> >  ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
> >  cxl_core-y := core.o
> >  cxl_pci-y := pci.o
> > +cxl_acpi-y := acpi.o
> > diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> > new file mode 100644
> > index 000000000000..556d25ab6966
> > --- /dev/null
> > +++ b/drivers/cxl/acpi.c
> > @@ -0,0 +1,39 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
> > +#include <linux/platform_device.h>
> > +#include <linux/module.h>
> > +#include <linux/device.h>
> > +#include <linux/kernel.h>
> > +#include <linux/acpi.h>
> > +#include "cxl.h"
> > +
> > +static int cxl_acpi_probe(struct platform_device *pdev)
> > +{
> > +     struct cxl_port *root_port;
> > +     struct device *host = &pdev->dev;
> > +
> > +     root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
> > +     if (IS_ERR(root_port))
> > +             return PTR_ERR(root_port);
> > +     dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
> > +
> > +     return 0;
> > +}
> > +
> > +static const struct acpi_device_id cxl_acpi_ids[] = {
> > +     { "ACPI0017", 0 },
> > +     { "", 0 },
> > +};
> > +MODULE_DEVICE_TABLE(acpi, cxl_acpi_ids);
> > +
> > +static struct platform_driver cxl_acpi_driver = {
> > +     .probe = cxl_acpi_probe,
> > +     .driver = {
> > +             .name = KBUILD_MODNAME,
> > +             .acpi_match_table = cxl_acpi_ids,
> > +     },
> > +};
> > +
> > +module_platform_driver(cxl_acpi_driver);
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_IMPORT_NS(CXL);
> > diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
> > index 853666d8a9f5..dbbb34618d7d 100644
> > --- a/drivers/cxl/core.c
> > +++ b/drivers/cxl/core.c
> > @@ -4,6 +4,8 @@
> >  #include <linux/device.h>
> >  #include <linux/module.h>
> >  #include <linux/pci.h>
> > +#include <linux/slab.h>
> > +#include <linux/idr.h>
> >  #include "cxl.h"
> >
> >  /**
> > @@ -13,6 +15,164 @@
> >   * point for cross-device interleave coordination through cxl ports.
> >   */
> >
> > +static DEFINE_IDA(cxl_port_ida);
> > +
> > +static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
> > +                         char *buf)
> > +{
> > +     return sysfs_emit(buf, "%s\n", dev->type->name);
>
> I guess it's really small so doesn't matter that much, but not so nice
> that we are gaining multiple instances of this same function.
>

This is only the second one unless I'm missing something. I do think
it might be worth placing a common definition in the driver-core.
Although it might be the case that I'm the only one that thinks having
devtype as both an attribute and a uevent variable (DEVTYPE) is
worthwhile. All the other variables in a dev_uevent() appear somewhere
in sysfs, so that's a decent argument in my opinion to make devtype a
core attribute.

Patch

diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
index 2fe7490ad6a8..fb996ced7629 100644
--- a/Documentation/ABI/testing/sysfs-bus-cxl
+++ b/Documentation/ABI/testing/sysfs-bus-cxl
@@ -24,3 +24,14 @@  Description:
 		(RO) "Persistent Only Capacity" as bytes. Represents the
 		identically named field in the Identify Memory Device Output
 		Payload in the CXL-2.0 specification.
+
+What:		/sys/bus/cxl/devices/portX/uport
+Date:		May, 2021
+KernelVersion:	v5.14
+Contact:	[e-mail]
+Description:
+		CXL port objects are enumerated from either a platform firmware
+		device (ACPI0017 and ACPI0016) or PCIe switch upstream port with
+		CXL component registers. The 'uport' symlink connects the CXL
+		portX object to the device that published the CXL port
+		capability.
diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 5483ba92b6da..d2573f6aef91 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -45,4 +45,19 @@  config CXL_MEM_RAW_COMMANDS
 	  potential impact to memory currently in use by the kernel.
 
 	  If developing CXL hardware or the driver say Y, otherwise say N.
+
+config CXL_ACPI
+	tristate "CXL ACPI: Platform Support"
+	depends on ACPI
+	help
+	  Enable support for host managed device memory (HDM) resources
+	  published by a platform's ACPI CXL memory layout description.  See
+	  Chapter 9.14.1 CXL Early Discovery Table (CEDT) in the CXL 2.0
+	  specification, and CXL Fixed Memory Window Structures (CEDT.CFMWS)
+	  (https://www.computeexpresslink.org/spec-landing). The CXL core
+	  consumes these resource to publish the root of a cxl_port decode
+	  hierarchy to map regions that represent System RAM, or Persistent
+	  Memory regions to be managed by LIBNVDIMM.
+
+	  If unsure say 'm'.
 endif
diff --git a/drivers/cxl/Makefile b/drivers/cxl/Makefile
index d9d282dc15be..a29efb3e8ad2 100644
--- a/drivers/cxl/Makefile
+++ b/drivers/cxl/Makefile
@@ -1,7 +1,9 @@ 
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_CXL_BUS) += cxl_core.o
 obj-$(CONFIG_CXL_MEM) += cxl_pci.o
+obj-$(CONFIG_CXL_ACPI) += cxl_acpi.o
 
 ccflags-y += -DDEFAULT_SYMBOL_NAMESPACE=CXL
 cxl_core-y := core.o
 cxl_pci-y := pci.o
+cxl_acpi-y := acpi.o
diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
new file mode 100644
index 000000000000..556d25ab6966
--- /dev/null
+++ b/drivers/cxl/acpi.c
@@ -0,0 +1,39 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright(c) 2021 Intel Corporation. All rights reserved. */
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/acpi.h>
+#include "cxl.h"
+
+static int cxl_acpi_probe(struct platform_device *pdev)
+{
+	struct cxl_port *root_port;
+	struct device *host = &pdev->dev;
+
+	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
+	if (IS_ERR(root_port))
+		return PTR_ERR(root_port);
+	dev_dbg(host, "add: %s\n", dev_name(&root_port->dev));
+
+	return 0;
+}
+
+static const struct acpi_device_id cxl_acpi_ids[] = {
+	{ "ACPI0017", 0 },
+	{ "", 0 },
+};
+MODULE_DEVICE_TABLE(acpi, cxl_acpi_ids);
+
+static struct platform_driver cxl_acpi_driver = {
+	.probe = cxl_acpi_probe,
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.acpi_match_table = cxl_acpi_ids,
+	},
+};
+
+module_platform_driver(cxl_acpi_driver);
+MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(CXL);
diff --git a/drivers/cxl/core.c b/drivers/cxl/core.c
index 853666d8a9f5..dbbb34618d7d 100644
--- a/drivers/cxl/core.c
+++ b/drivers/cxl/core.c
@@ -4,6 +4,8 @@ 
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/slab.h>
+#include <linux/idr.h>
 #include "cxl.h"
 
 /**
@@ -13,6 +15,164 @@ 
  * point for cross-device interleave coordination through cxl ports.
  */
 
+static DEFINE_IDA(cxl_port_ida);
+
+static ssize_t devtype_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	return sysfs_emit(buf, "%s\n", dev->type->name);
+}
+static DEVICE_ATTR_RO(devtype);
+
+static struct attribute *cxl_base_attributes[] = {
+	&dev_attr_devtype.attr,
+	NULL,
+};
+
+static struct attribute_group cxl_base_attribute_group = {
+	.attrs = cxl_base_attributes,
+};
+
+static void cxl_port_release(struct device *dev)
+{
+	struct cxl_port *port = to_cxl_port(dev);
+
+	ida_free(&cxl_port_ida, port->id);
+	kfree(port);
+}
+
+static const struct attribute_group *cxl_port_attribute_groups[] = {
+	&cxl_base_attribute_group,
+	NULL,
+};
+
+static const struct device_type cxl_port_type = {
+	.name = "cxl_port",
+	.release = cxl_port_release,
+	.groups = cxl_port_attribute_groups,
+};
+
+struct cxl_port *to_cxl_port(struct device *dev)
+{
+	if (dev_WARN_ONCE(dev, dev->type != &cxl_port_type,
+			  "not a cxl_port device\n"))
+		return NULL;
+	return container_of(dev, struct cxl_port, dev);
+}
+
+static void unregister_dev(void *dev)
+{
+	device_unregister(dev);
+}
+
+static void cxl_unlink_uport(void *_port)
+{
+	struct cxl_port *port = _port;
+
+	sysfs_remove_link(&port->dev.kobj, "uport");
+}
+
+static int devm_cxl_link_uport(struct device *host, struct cxl_port *port)
+{
+	int rc;
+
+	rc = sysfs_create_link(&port->dev.kobj, &port->uport->kobj, "uport");
+	if (rc)
+		return rc;
+	return devm_add_action_or_reset(host, cxl_unlink_uport, port);
+}
+
+static struct cxl_port *cxl_port_alloc(struct device *uport,
+				       resource_size_t component_reg_phys,
+				       struct cxl_port *parent_port)
+{
+	struct cxl_port *port;
+	struct device *dev;
+	int rc;
+
+	port = kzalloc(sizeof(*port), GFP_KERNEL);
+	if (!port)
+		return ERR_PTR(-ENOMEM);
+
+	rc = ida_alloc(&cxl_port_ida, GFP_KERNEL);
+	if (rc < 0)
+		goto err;
+	port->id = rc;
+
+	/*
+	 * The top-level cxl_port "cxl_root" does not have a cxl_port as
+	 * its parent and it does not have any corresponding component
+	 * registers as its decode is described by a fixed platform
+	 * description.
+	 */
+	dev = &port->dev;
+	if (parent_port)
+		dev->parent = &parent_port->dev;
+	else
+		dev->parent = uport;
+
+	port->uport = uport;
+	port->component_reg_phys = component_reg_phys;
+
+	device_initialize(dev);
+	device_set_pm_not_required(dev);
+	dev->bus = &cxl_bus_type;
+	dev->type = &cxl_port_type;
+
+	return port;
+
+err:
+	kfree(port);
+	return ERR_PTR(rc);
+}
+
+/**
+ * devm_cxl_add_port - register a cxl_port in CXL memory decode hierarchy
+ * @host: host device for devm operations
+ * @uport: "physical" device implementing this upstream port
+ * @component_reg_phys: (optional) for configurable cxl_port instances
+ * @parent_port: next hop up in the CXL memory decode hierarchy
+ */
+struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
+				   resource_size_t component_reg_phys,
+				   struct cxl_port *parent_port)
+{
+	struct cxl_port *port;
+	struct device *dev;
+	int rc;
+
+	port = cxl_port_alloc(uport, component_reg_phys, parent_port);
+	if (IS_ERR(port))
+		return port;
+
+	dev = &port->dev;
+	if (parent_port)
+		rc = dev_set_name(dev, "port%d", port->id);
+	else
+		rc = dev_set_name(dev, "root%d", port->id);
+	if (rc)
+		goto err;
+
+	rc = device_add(dev);
+	if (rc)
+		goto err;
+
+	rc = devm_add_action_or_reset(host, unregister_dev, dev);
+	if (rc)
+		return ERR_PTR(rc);
+
+	rc = devm_cxl_link_uport(host, port);
+	if (rc)
+		return ERR_PTR(rc);
+
+	return port;
+
+err:
+	put_device(dev);
+	return ERR_PTR(rc);
+}
+EXPORT_SYMBOL_GPL(devm_cxl_add_port);
+
 /**
  * cxl_probe_component_regs() - Detect CXL Component register blocks
  * @dev: Host device of the @base mapping
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index 2c47e9cffd44..46c81165c210 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -145,5 +145,28 @@  int cxl_map_device_regs(struct pci_dev *pdev,
 			struct cxl_device_regs *regs,
 			struct cxl_register_map *map);
 
+#define CXL_RESOURCE_NONE ((resource_size_t) -1)
+
+/**
+ * struct cxl_port - logical collection of upstream port devices and
+ *		     downstream port devices to construct a CXL memory
+ *		     decode hierarchy.
+ * @dev: this port's device
+ * @uport: PCI or platform device implementing the upstream port capability
+ * @id: id for port device-name
+ * @component_regs_phys: component register capability base address (optional)
+ */
+struct cxl_port {
+	struct device dev;
+	struct device *uport;
+	int id;
+	resource_size_t component_reg_phys;
+};
+
+struct cxl_port *to_cxl_port(struct device *dev);
+struct cxl_port *devm_cxl_add_port(struct device *host, struct device *uport,
+				   resource_size_t component_reg_phys,
+				   struct cxl_port *parent_port);
+
 extern struct bus_type cxl_bus_type;
 #endif /* __CXL_H__ */