cxl/pmem: add provider name to cxl pmem dimm attribute group

Add provider name in order to associate cxl test dimm from cxl_test to the
cxl pmem device when going through sysfs for security testing.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/166983618174.2734609.15600031015423828810.stgit@djiang5-desk3.ch.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/ABI/testing/sysfs-bus-nvdimm

@@ -47,3 +47,11 @@ Date:		November 2022
 KernelVersion:	6.2
 Contact:	Dave Jiang <dave.jiang@intel.com>
 Description:	(RO) Show the id (serial) of the device. This is CXL specific.
+
+What:		/sys/bus/nd/devices/nmemX/cxl/provider
+Date:		November 2022
+KernelVersion:	6.2
+Contact:	Dave Jiang <dave.jiang@intel.com>
+Description:	(RO) Shows the CXL bridge device that ties to a CXL memory device
+		to this NVDIMM device. I.e. the parent of the device returned is
+		a /sys/bus/cxl/devices/memX instance.

drivers/cxl/pmem.c

@@ -51,6 +51,15 @@ static void unregister_nvdimm(void *nvdimm)
 	cxl_nvd->bridge = NULL;
 }
 
+static ssize_t provider_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct nvdimm *nvdimm = to_nvdimm(dev);
+	struct cxl_nvdimm *cxl_nvd = nvdimm_provider_data(nvdimm);
+
+	return sysfs_emit(buf, "%s\n", dev_name(&cxl_nvd->dev));
+}
+static DEVICE_ATTR_RO(provider);
+
 static ssize_t id_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	struct nvdimm *nvdimm = to_nvdimm(dev);
@@ -63,6 +72,7 @@ static DEVICE_ATTR_RO(id);
 
 static struct attribute *cxl_dimm_attributes[] = {
 	&dev_attr_id.attr,
+	&dev_attr_provider.attr,
 	NULL
 };