Commit 29317f8d authored by Dan Williams's avatar Dan Williams Committed by Dave Jiang
Browse files

cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation 



Unlike the cxl_pci class driver that opportunistically enables memory
expansion with no other dependent functionality, CXL accelerator drivers
have distinct PCIe-only and CXL-enhanced operation states. If CXL is
available some additional coherent memory/cache operations can be enabled,
otherwise traditional DMA+MMIO over PCIe/CXL.io is a fallback.

This constitutes a new mode of operation where the caller of
devm_cxl_add_memdev() wants to make a "go/no-go" decision about running
in CXL accelerated mode or falling back to PCIe-only operation. Part of
that decision making process likely also includes additional
CXL-acceleration-specific resource setup. Encapsulate both of those
requirements into 'struct cxl_memdev_attach' that provides a ->probe()
callback. The probe callback runs in cxl_mem_probe() context, after the
port topology is successfully attached for the given memdev. It supports
a contract where, upon successful return from devm_cxl_add_memdev(),
everything needed for CXL accelerated operation has been enabled.

Additionally the presence of @cxlmd->attach indicates that the accelerator
driver be detached when CXL operation ends. This conceptually makes a CXL
link loss event mirror a PCIe link loss event which results in triggering
the ->remove() callback of affected devices+drivers. A driver can re-attach
to recover back to PCIe-only operation. Live recovery, i.e. without a
->remove()/->probe() cycle, is left as a future consideration.

[ dj: Repalce with updated commit log from Dan ]

Cc: Smita Koralahalli <Smita.KoralahalliChannabasappa@amd.com>
Reviewed-by: default avatarBen Cheatham <benjamin.cheatham@amd.com>
Reviewed-by: default avatarDave Jiang <dave.jiang@intel.com>
Tested-by: default avatarAlejandro Lucero <alucerop@amd.com>
Reviewed-by: default avatarJonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251216005616.3090129-7-dan.j.williams@intel.com


Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarDave Jiang <dave.jiang@intel.com>
parent f2546eba

drivers/cxl/core/memdev.c

+29 −4
Original line number Diff line number Diff line
@@ -641,6 +641,15 @@ static void detach_memdev(struct work_struct *work) 
	struct cxl_memdev *cxlmd;



	cxlmd = container_of(work, typeof(*cxlmd), detach_work);



	/*

	 * When the creator of @cxlmd sets ->attach it indicates CXL operation

	 * is required. In that case, @cxlmd detach escalates to parent device

	 * detach.

	 */

	if (cxlmd->attach)

		device_release_driver(cxlmd->dev.parent);

	else

		device_release_driver(&cxlmd->dev);

	put_device(&cxlmd->dev);

}
@@ -648,7 +657,8 @@ static void detach_memdev(struct work_struct *work) 
static struct lock_class_key cxl_memdev_key;



static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,

					   const struct file_operations *fops)

					   const struct file_operations *fops,

					   const struct cxl_memdev_attach *attach)

{

	struct cxl_memdev *cxlmd;

	struct device *dev;
@@ -664,6 +674,8 @@ static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds, 
		goto err;

	cxlmd->id = rc;

	cxlmd->depth = -1;

	cxlmd->attach = attach;

	cxlmd->endpoint = ERR_PTR(-ENXIO);



	dev = &cxlmd->dev;

	device_initialize(dev);
@@ -1081,6 +1093,18 @@ static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd) 
{

	int rc;



	/*

	 * If @attach is provided fail if the driver is not attached upon

	 * return. Note that failure here could be the result of a race to

	 * teardown the CXL port topology. I.e. cxl_mem_probe() could have

	 * succeeded and then cxl_mem unbound before the lock is acquired.

	 */

	guard(device)(&cxlmd->dev);

	if (cxlmd->attach && !cxlmd->dev.driver) {

		cxl_memdev_unregister(cxlmd);

		return ERR_PTR(-ENXIO);

	}



	rc = devm_add_action_or_reset(cxlmd->cxlds->dev, cxl_memdev_unregister,

				      cxlmd);

	if (rc)
@@ -1093,13 +1117,14 @@ static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd) 
 * Core helper for devm_cxl_add_memdev() that wants to both create a device and

 * assert to the caller that upon return cxl_mem::probe() has been invoked.

 */

struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds)

struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds,

					 const struct cxl_memdev_attach *attach)

{

	struct device *dev;

	int rc;



	struct cxl_memdev *cxlmd __free(put_cxlmd) =

		cxl_memdev_alloc(cxlds, &cxl_memdev_fops);

		cxl_memdev_alloc(cxlds, &cxl_memdev_fops, attach);

	if (IS_ERR(cxlmd))

		return cxlmd;

drivers/cxl/cxlmem.h

+10 −2
Original line number Diff line number Diff line
@@ -34,6 +34,10 @@ 
	(FIELD_GET(CXLMDEV_RESET_NEEDED_MASK, status) !=                       \

	 CXLMDEV_RESET_NEEDED_NOT)



struct cxl_memdev_attach {

	int (*probe)(struct cxl_memdev *cxlmd);

};



/**

 * struct cxl_memdev - CXL bus object representing a Type-3 Memory Device

 * @dev: driver core device object
@@ -43,6 +47,7 @@ 
 * @cxl_nvb: coordinate removal of @cxl_nvd if present

 * @cxl_nvd: optional bridge to an nvdimm if the device supports pmem

 * @endpoint: connection to the CXL port topology for this memory device

 * @attach: creator of this memdev depends on CXL link attach to operate

 * @id: id number of this memdev instance.

 * @depth: endpoint port depth

 * @scrub_cycle: current scrub cycle set for this device
@@ -59,6 +64,7 @@ struct cxl_memdev { 
	struct cxl_nvdimm_bridge *cxl_nvb;

	struct cxl_nvdimm *cxl_nvd;

	struct cxl_port *endpoint;

	const struct cxl_memdev_attach *attach;

	int id;

	int depth;

	u8 scrub_cycle;
@@ -95,8 +101,10 @@ static inline bool is_cxl_endpoint(struct cxl_port *port) 
	return is_cxl_memdev(port->uport_dev);

}



struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds);

struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds);

struct cxl_memdev *__devm_cxl_add_memdev(struct cxl_dev_state *cxlds,

					 const struct cxl_memdev_attach *attach);

struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds,

				       const struct cxl_memdev_attach *attach);

int devm_cxl_sanitize_setup_notifier(struct device *host,

				     struct cxl_memdev *cxlmd);

struct cxl_memdev_state;

drivers/cxl/mem.c

+16 −4
Original line number Diff line number Diff line
@@ -142,6 +142,12 @@ static int cxl_mem_probe(struct device *dev) 
			return rc;

	}



	if (cxlmd->attach) {

		rc = cxlmd->attach->probe(cxlmd);

		if (rc)

			return rc;

	}



	rc = devm_cxl_memdev_edac_register(cxlmd);

	if (rc)

		dev_dbg(dev, "CXL memdev EDAC registration failed rc=%d\n", rc);
@@ -166,17 +172,23 @@ static int cxl_mem_probe(struct device *dev) 
/**

 * devm_cxl_add_memdev - Add a CXL memory device

 * @cxlds: CXL device state to associate with the memdev

 * @attach: Caller depends on CXL topology attachment

 *

 * Upon return the device will have had a chance to attach to the

 * cxl_mem driver, but may fail if the CXL topology is not ready

 * (hardware CXL link down, or software platform CXL root not attached)

 * cxl_mem driver, but may fail to attach if the CXL topology is not ready

 * (hardware CXL link down, or software platform CXL root not attached).

 *

 * When @attach is NULL it indicates the caller wants the memdev to remain

 * registered even if it does not immediately attach to the CXL hierarchy. When

 * @attach is provided a cxl_mem_probe() failure leads to failure of this routine.

 *

 * The parent of the resulting device and the devm context for allocations is

 * @cxlds->dev.

 */

struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)

struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds,

				       const struct cxl_memdev_attach *attach)

{

	return __devm_cxl_add_memdev(cxlds);

	return __devm_cxl_add_memdev(cxlds, attach);

}

EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");

drivers/cxl/pci.c

+1 −1
Original line number Diff line number Diff line
@@ -1006,7 +1006,7 @@ static int cxl_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id) 
	if (rc)

		dev_dbg(&pdev->dev, "No CXL Features discovered\n");



	cxlmd = devm_cxl_add_memdev(cxlds);

	cxlmd = devm_cxl_add_memdev(cxlds, NULL);

	if (IS_ERR(cxlmd))

		return PTR_ERR(cxlmd);

tools/testing/cxl/test/mem.c

+1 −1
Original line number Diff line number Diff line
@@ -1767,7 +1767,7 @@ static int cxl_mock_mem_probe(struct platform_device *pdev) 


	cxl_mock_add_event_logs(&mdata->mes);



	cxlmd = devm_cxl_add_memdev(cxlds);

	cxlmd = devm_cxl_add_memdev(cxlds, NULL);

	if (IS_ERR(cxlmd))

		return PTR_ERR(cxlmd);