ACPI: scan: Avoid enumerating devices with clearly invalid _STA values

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/[e-mail]/
Suggested-by: Salil Mehta <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Sudeep Holla <[e-mail]>

drivers/acpi/bus.c

···
 	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) {

drivers/acpi/scan.c

···
 
 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,