cxl/mem: Fix no cxl_nvd during pmem region auto-assembling

When CXL subsystem is auto-assembling a pmem region during cxl
endpoint port probing, always hit below calltrace.

 BUG: kernel NULL pointer dereference, address: 0000000000000078
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 RIP: 0010:cxl_pmem_region_probe+0x22e/0x360 [cxl_pmem]
 Call Trace:
  <TASK>
  ? __die+0x24/0x70
  ? page_fault_oops+0x82/0x160
  ? do_user_addr_fault+0x65/0x6b0
  ? exc_page_fault+0x7d/0x170
  ? asm_exc_page_fault+0x26/0x30
  ? cxl_pmem_region_probe+0x22e/0x360 [cxl_pmem]
  ? cxl_pmem_region_probe+0x1ac/0x360 [cxl_pmem]
  cxl_bus_probe+0x1b/0x60 [cxl_core]
  really_probe+0x173/0x410
  ? __pfx___device_attach_driver+0x10/0x10
  __driver_probe_device+0x80/0x170
  driver_probe_device+0x1e/0x90
  __device_attach_driver+0x90/0x120
  bus_for_each_drv+0x84/0xe0
  __device_attach+0xbc/0x1f0
  bus_probe_device+0x90/0xa0
  device_add+0x51c/0x710
  devm_cxl_add_pmem_region+0x1b5/0x380 [cxl_core]
  cxl_bus_probe+0x1b/0x60 [cxl_core]

The cxl_nvd of the memdev needs to be available during the pmem region
probe. Currently the cxl_nvd is registered after the endpoint port probe.
The endpoint probe, in the case of autoassembly of regions, can cause a
pmem region probe requiring the not yet available cxl_nvd. Adjust the
sequence so this dependency is met.

This requires adding a port parameter to cxl_find_nvdimm_bridge() that
can be used to query the ancestor root port. The endpoint port is not
yet available, but will share a common ancestor with its parent, so
start the query from there instead.

Fixes: f17b558 ("cxl/pmem: Refactor nvdimm device registration, delete the workqueue")
Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Li Ming <ming4.li@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Link: https://patch.msgid.link/20240612064423.2567625-1-ming4.li@intel.com
Signed-off-by: Dave Jiang <dave.jiang@intel.com>

drivers/cxl/core/pmem.c

@@ -62,10 +62,14 @@ static int match_nvdimm_bridge(struct device *dev, void *data)
  return is_cxl_nvdimm_bridge(dev);
 }
 
-struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_memdev *cxlmd)
+/**
+ * cxl_find_nvdimm_bridge() - find a bridge device relative to a port
+ * @port: any descendant port of an nvdimm-bridge associated
+ * root-cxl-port
+ */
+struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_port *port)
 {
- struct cxl_root *cxl_root __free(put_cxl_root) =
- find_cxl_root(cxlmd->endpoint);
+ struct cxl_root *cxl_root __free(put_cxl_root) = find_cxl_root(port);
  struct device *dev;
 
  if (!cxl_root)
@@ -242,18 +246,20 @@ static void cxlmd_release_nvdimm(void *_cxlmd)
 
 /**
  * devm_cxl_add_nvdimm() - add a bridge between a cxl_memdev and an nvdimm
+ * @parent_port: parent port for the (to be added) @cxlmd endpoint port
  * @cxlmd: cxl_memdev instance that will perform LIBNVDIMM operations
  *
  * Return: 0 on success negative error code on failure.
  */
-int devm_cxl_add_nvdimm(struct cxl_memdev *cxlmd)
+int devm_cxl_add_nvdimm(struct cxl_port *parent_port,
+ struct cxl_memdev *cxlmd)
 {
  struct cxl_nvdimm_bridge *cxl_nvb;
  struct cxl_nvdimm *cxl_nvd;
  struct device *dev;
  int rc;
 
- cxl_nvb = cxl_find_nvdimm_bridge(cxlmd);
+ cxl_nvb = cxl_find_nvdimm_bridge(parent_port);
  if (!cxl_nvb)
  return -ENODEV;
 

drivers/cxl/core/region.c

@@ -2847,7 +2847,7 @@ static int cxl_pmem_region_alloc(struct cxl_region *cxlr)
  * bridge for one device is the same for all.
  */
  if (i == 0) {
- cxl_nvb = cxl_find_nvdimm_bridge(cxlmd);
+ cxl_nvb = cxl_find_nvdimm_bridge(cxlmd->endpoint);
  if (!cxl_nvb)
  return -ENODEV;
  cxlr->cxl_nvb = cxl_nvb;

drivers/cxl/cxl.h

@@ -855,8 +855,8 @@ struct cxl_nvdimm_bridge *devm_cxl_add_nvdimm_bridge(struct device *host,
 struct cxl_nvdimm *to_cxl_nvdimm(struct device *dev);
 bool is_cxl_nvdimm(struct device *dev);
 bool is_cxl_nvdimm_bridge(struct device *dev);
-int devm_cxl_add_nvdimm(struct cxl_memdev *cxlmd);
-struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_memdev *cxlmd);
+int devm_cxl_add_nvdimm(struct cxl_port *parent_port, struct cxl_memdev *cxlmd);
+struct cxl_nvdimm_bridge *cxl_find_nvdimm_bridge(struct cxl_port *port);
 
 #ifdef CONFIG_CXL_REGION
 bool is_cxl_pmem_region(struct device *dev);

drivers/cxl/mem.c

@@ -152,6 +152,15 @@ static int cxl_mem_probe(struct device *dev)
  return -ENXIO;
  }
 
+ if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM)) {
+ rc = devm_cxl_add_nvdimm(parent_port, cxlmd);
+ if (rc) {
+ if (rc == -ENODEV)
+ dev_info(dev, "PMEM disabled by platform\n");
+ return rc;
+ }
+ }
+
  if (dport->rch)
  endpoint_parent = parent_port->uport_dev;
  else
@@ -174,14 +183,6 @@ static int cxl_mem_probe(struct device *dev)
  if (rc)
  return rc;
 
- if (resource_size(&cxlds->pmem_res) && IS_ENABLED(CONFIG_CXL_PMEM)) {
- rc = devm_cxl_add_nvdimm(cxlmd);
- if (rc == -ENODEV)
- dev_info(dev, "PMEM disabled by platform\n");
- else
- return rc;
- }
-
  /*
  * The kernel may be operating out of CXL memory on this device,
  * there is no spec defined way to determine whether this device