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.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/drivers/cxl/mem.h b/drivers/cxl/mem.h
index 0a3f703..23fc40d 100644
--- a/drivers/cxl/mem.h
+++ b/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;