acpi, nfit: Prefer _DSM over _LSR for namespace label reads

The _LSR method indicates locked status via error-code-3 returned in the
_LSR payload. When any error is returned the payload of _LSR is
truncated to a zero-length buffer.

The _DSM path in comparison allows system software to retrieve the
locked status *and* namespace label area contents.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/acpi/nfit/core.c

@@ -1697,7 +1697,7 @@ static int acpi_nfit_add_dimm(struct acpi_nfit_desc *acpi_desc,
 {
 	struct acpi_device *adev, *adev_dimm;
 	struct device *dev = acpi_desc->dev;
-	unsigned long dsm_mask;
+	unsigned long dsm_mask, label_mask;
 	const guid_t *guid;
 	int i;
 	int family = -1;
@@ -1769,6 +1769,16 @@ static int acpi_nfit_add_dimm(struct acpi_nfit_desc *acpi_desc,
 					1ULL << i))
 			set_bit(i, &nfit_mem->dsm_mask);
 
+	/*
+	 * Prefer the NVDIMM_FAMILY_INTEL label read commands if present
+	 * due to their better semantics handling locked capacity.
+	 */
+	label_mask = 1 << ND_CMD_GET_CONFIG_SIZE | 1 << ND_CMD_GET_CONFIG_DATA
+		| 1 << ND_CMD_SET_CONFIG_DATA;
+	if (family == NVDIMM_FAMILY_INTEL
+			&& (dsm_mask & label_mask) == label_mask)
+		return 0;
+
 	if (acpi_nvdimm_has_method(adev_dimm, "_LSI")
 			&& acpi_nvdimm_has_method(adev_dimm, "_LSR")) {
 		dev_dbg(dev, "%s: has _LSR\n", dev_name(&adev_dimm->dev));