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

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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 <alison.schofield@xxxxxxxxx>
> Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  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:	linux-cxl@xxxxxxxxxxxxxxx
> +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__ */
> 




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