cxl/pci.c: Add a 'label_storage_size' attribute to the memdev

The 'Identify Device' mailbox command returns an 'lsa_size', which is
the size of the label storage area on the device. Export it as a sysfs
attribute so that userspace tooling to read/write the LSA can determine
the size without having to run an 'Identify Device' on their own.

Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/20210520194745.1095517-1-vishal.l.verma@intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/mem.h

@@ -54,6 +54,8 @@ struct cxl_memdev {
  * @regs: Parsed register blocks
  * @payload_size: Size of space for payload
  *                (CXL 2.0 8.2.8.4.3 Mailbox Capabilities Register)
+ * @lsa_size: Size of Label Storage Area
+ *                (CXL 2.0 8.2.9.5.1.1 Identify Memory Device)
  * @mbox_mutex: Mutex to synchronize mailbox access.
  * @firmware_version: Firmware version for the memory device.
  * @enabled_cmds: Hardware commands found enabled in CEL.
@@ -68,6 +70,7 @@ struct cxl_mem {
 	struct cxl_regs regs;
 
 	size_t payload_size;
+	size_t lsa_size;
 	struct mutex mbox_mutex; /* Protects device mailbox and firmware */
 	char firmware_version[0x10];
 	unsigned long *enabled_cmds;

drivers/cxl/pci.c

@@ -1036,6 +1036,16 @@ static ssize_t payload_max_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(payload_max);
 
+static ssize_t label_storage_size_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
+	struct cxl_mem *cxlm = cxlmd->cxlm;
+
+	return sysfs_emit(buf, "%zu\n", cxlm->lsa_size);
+}
+static DEVICE_ATTR_RO(label_storage_size);
+
 static ssize_t ram_size_show(struct device *dev, struct device_attribute *attr,
 			     char *buf)
 {
@@ -1065,6 +1075,7 @@ static struct device_attribute dev_attr_pmem_size =
 static struct attribute *cxl_memdev_attributes[] = {
 	&dev_attr_firmware_version.attr,
 	&dev_attr_payload_max.attr,
+	&dev_attr_label_storage_size.attr,
 	NULL,
 };
 
@@ -1397,6 +1408,7 @@ static int cxl_mem_identify(struct cxl_mem *cxlm)
 	cxlm->pmem_range.end =
 		le64_to_cpu(id.persistent_capacity) * SZ_256M - 1;
 
+	cxlm->lsa_size = le32_to_cpu(id.lsa_size);
 	memcpy(cxlm->firmware_version, id.fw_revision, sizeof(id.fw_revision));
 
 	return 0;