ACPICA: Update comments about behavior when _STA does not exist

No functional change.  Add some comments concerning behavior
when the _STA method does not exist. According to the ACPI
specification, in this case the device should be assumed to be
present, functional, and enabled.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Acked-by: Len Brown <len.brown@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 13 insertions, 2 deletions

diff --git a/drivers/acpi/acpica/nsxfname.c b/drivers/acpi/acpica/nsxfname.c
index f3a4d95899f7..21a2ef363ad4 100644
--- a/drivers/acpi/acpica/nsxfname.c
+++ b/drivers/acpi/acpica/nsxfname.c
@@ -379,9 +379,14 @@ acpi_get_object_info(acpi_handle handle,
                  * Get extra info for ACPI Device/Processor objects only:
                  * Run the _STA, _ADR and, sx_w, and _sx_d methods.
                  *
-                 * Note: none of these methods are required, so they may or may
+                 * Notes: none of these methods are required, so they may or may
                  * not be present for this device. The Info->Valid bitfield is used
                  * to indicate which methods were found and run successfully.
+                 *
+                 * For _STA, if the method does not exist, then (as per the ACPI
+                 * specification), the returned current_status flags will indicate
+                 * that the device is present/functional/enabled. Otherwise, the
+                 * current_status flags reflect the value returned from _STA.
                  */
 
                 /* Execute the Device._STA method */
diff --git a/drivers/acpi/acpica/uteval.c b/drivers/acpi/acpica/uteval.c
index ee83adb97b1e..4fd68971019b 100644
--- a/drivers/acpi/acpica/uteval.c
+++ b/drivers/acpi/acpica/uteval.c
@@ -239,7 +239,8 @@ acpi_ut_evaluate_numeric_object(char *object_name,
  * RETURN:      Status
  *
  * DESCRIPTION: Executes _STA for selected device and stores results in
- *              *Flags.
+ *              *Flags. If _STA does not exist, then the device is assumed
+ *              to be present/functional/enabled (as per the ACPI spec).
  *
  *              NOTE: Internal function, no parameter validation
  *
@@ -257,6 +258,11 @@ acpi_ut_execute_STA(struct acpi_namespace_node *device_node, u32 * flags)
                                          ACPI_BTYPE_INTEGER, &obj_desc);
         if (ACPI_FAILURE(status)) {
                 if (AE_NOT_FOUND == status) {
+                        /*
+                         * if _STA does not exist, then (as per the ACPI specification),
+                         * the returned flags will indicate that the device is present,
+                         * functional, and enabled.
+                         */
                         ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
                                           "_STA on %4.4s was not found, assuming device is present\n",
                                           acpi_ut_get_node_name(device_node)));