nfit: export subsystem ids as attributes

Similar to pci-sysfs export the subsystem information available in the
NFIT.  ACPI 6.1 clarifies that this data is copied as an array of bytes
from the DIMM SPD data.
Reported-by: NRyon Jensen <ryon.jensen@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit.c

@@ -847,6 +847,34 @@ static ssize_t format_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(format);
 
+static ssize_t subsystem_vendor_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct acpi_nfit_control_region *dcr = to_nfit_dcr(dev);
+
+	return sprintf(buf, "0x%04x\n", be16_to_cpu(dcr->subsystem_vendor_id));
+}
+static DEVICE_ATTR_RO(subsystem_vendor);
+
+static ssize_t subsystem_rev_id_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct acpi_nfit_control_region *dcr = to_nfit_dcr(dev);
+
+	return sprintf(buf, "0x%04x\n",
+			be16_to_cpu(dcr->subsystem_revision_id));
+}
+static DEVICE_ATTR_RO(subsystem_rev_id);
+
+static ssize_t subsystem_device_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct acpi_nfit_control_region *dcr = to_nfit_dcr(dev);
+
+	return sprintf(buf, "0x%04x\n", be16_to_cpu(dcr->subsystem_device_id));
+}
+static DEVICE_ATTR_RO(subsystem_device);
+
 static ssize_t serial_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -893,9 +921,12 @@ static struct attribute *acpi_nfit_dimm_attributes[] = {
 	&dev_attr_phys_id.attr,
 	&dev_attr_vendor.attr,
 	&dev_attr_device.attr,
+	&dev_attr_rev_id.attr,
+	&dev_attr_subsystem_vendor.attr,
+	&dev_attr_subsystem_device.attr,
+	&dev_attr_subsystem_rev_id.attr,
 	&dev_attr_format.attr,
 	&dev_attr_serial.attr,
-	&dev_attr_rev_id.attr,
 	&dev_attr_flags.attr,
 	&dev_attr_id.attr,
 	NULL,