[PATCH v2] ACPI: scan: Avoid enumerating devices with clearly invalid _STA values

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The return value of _STA with the "present" bit unset and the "enabled"
bit set is clearly invalid as per the ACPI specification, Section 6.3.7
"_STA (Device Status)", so make the ACPI device enumeration code
disregard devices with such _STA return values.

Also, because this implies that status.enabled will only be set if
status.present is set too, acpi_device_is_enabled() can be modified
to simply return the value of the former.

Link: https://uefi.org/specs/ACPI/6.5/06_Device_Configuration.html#sta-device-status
Link: https://lore.kernel.org/linux-acpi/88179311a503493099028c12ca37d430@huawei.com/
Suggested-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
---

v1 -> v2:
   * Fix a confusing comment.
   * Add R-by from Jonathan (thank you!)

---
 drivers/acpi/bus.c  |   11 +++++++++++
 drivers/acpi/scan.c |    2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/acpi/bus.c
===================================================================
--- linux-pm.orig/drivers/acpi/bus.c
+++ linux-pm/drivers/acpi/bus.c
@@ -112,6 +112,17 @@ int acpi_bus_get_status(struct acpi_devi
 	if (ACPI_FAILURE(status))
 		return -ENODEV;
 
+	if (!device->status.present && device->status.enabled) {
+		pr_info(FW_BUG "Device [%s] status [%08x]: not present and enabled\n",
+			device->pnp.bus_id, (u32)sta);
+		device->status.enabled = 0;
+		/*
+		 * The status is clearly invalid, so clear the functional bit as
+		 * well to avoid attempting to use the device.
+		 */
+		device->status.functional = 0;
+	}
+
 	acpi_set_device_status(device, sta);
 
 	if (device->status.functional && !device->status.present) {
Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -1962,7 +1962,7 @@ bool acpi_device_is_present(const struct
 
 bool acpi_device_is_enabled(const struct acpi_device *adev)
 {
-	return adev->status.present && adev->status.enabled;
+	return adev->status.enabled;
 }
 
 static bool acpi_scan_handler_matching(struct acpi_scan_handler *handler,