cxl/pmem: add id attribute to CXL based nvdimm

Add an id group attribute for CXL based nvdimm object. The addition allows
ndctl to display the "unique id" for the nvdimm. The serial number for the
CXL memory device will be used for this id.

[
  {
      "dev":"nmem10",
      "id":"0x4",
      "security":"disabled"
  },
]

The id attribute is needed by the ndctl security key management to setup a
keyblob with a unique file name tied to the mem device.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/166983617029.2734609.8251308562882142281.stgit@djiang5-desk3.ch.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

Documentation/ABI/testing/sysfs-bus-nvdimm

@@ -41,3 +41,9 @@ KernelVersion:  5.18
 Contact:        Kajol Jain <kjain@linux.ibm.com>
 Description:	(RO) This sysfs file exposes the cpumask which is designated to
 		to retrieve nvdimm pmu event counter data.
+
+What:		/sys/bus/nd/devices/nmemX/cxl/id
+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.

drivers/cxl/pmem.c

@@ -51,6 +51,31 @@ static void unregister_nvdimm(void *nvdimm)
 	cxl_nvd->bridge = NULL;
 }
 
+static ssize_t id_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);
+	struct cxl_dev_state *cxlds = cxl_nvd->cxlmd->cxlds;
+
+	return sysfs_emit(buf, "%lld\n", cxlds->serial);
+}
+static DEVICE_ATTR_RO(id);
+
+static struct attribute *cxl_dimm_attributes[] = {
+	&dev_attr_id.attr,
+	NULL
+};
+
+static const struct attribute_group cxl_dimm_attribute_group = {
+	.name = "cxl",
+	.attrs = cxl_dimm_attributes,
+};
+
+static const struct attribute_group *cxl_dimm_attribute_groups[] = {
+	&cxl_dimm_attribute_group,
+	NULL
+};
+
 static int cxl_nvdimm_probe(struct device *dev)
 {
 	struct cxl_nvdimm *cxl_nvd = to_cxl_nvdimm(dev);
@@ -80,7 +105,8 @@ static int cxl_nvdimm_probe(struct device *dev)
 	set_bit(ND_CMD_GET_CONFIG_SIZE, &cmd_mask);
 	set_bit(ND_CMD_GET_CONFIG_DATA, &cmd_mask);
 	set_bit(ND_CMD_SET_CONFIG_DATA, &cmd_mask);
-	nvdimm = __nvdimm_create(cxl_nvb->nvdimm_bus, cxl_nvd, NULL, flags,
+	nvdimm = __nvdimm_create(cxl_nvb->nvdimm_bus, cxl_nvd,
+				 cxl_dimm_attribute_groups, flags,
 				 cmd_mask, 0, NULL, NULL, cxl_security_ops, NULL);
 	if (!nvdimm) {
 		rc = -ENOMEM;