@@ -537,16 +537,6 @@ static const struct dmi_system_id video_detect_dmi_table[] = {
/*
* Determine which type of backlight interface to use on this system,
* First check cmdline, then dmi quirks, then do autodetect.
- *
- * The autodetect order is:
- * 1) Is the acpi-video backlight interface supported ->
- * no, use a vendor interface
- * 2) Is this a win8 "ready" BIOS and do we have a native interface ->
- * yes, use a native interface
- * 3) Else use the acpi-video interface
- *
- * Arguably the native on win8 check should be done first, but that would
- * be a behavior change, which may causes issues.
*/
static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
{
@@ -569,19 +559,36 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
native_available = true;
mutex_unlock(&init_mutex);
+ /*
+ * The below heuristics / detection steps are in order of descending
+ * presedence. The commandline takes presedence over anything else.
+ */
if (acpi_backlight_cmdline != acpi_backlight_undef)
return acpi_backlight_cmdline;
+ /* DMI quirks override any autodetection. */
if (acpi_backlight_dmi != acpi_backlight_undef)
return acpi_backlight_dmi;
- if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
- return acpi_backlight_vendor;
-
- if (acpi_osi_is_win8() && native_available)
- return acpi_backlight_native;
+ /* On systems with ACPI video use either native or ACPI video. */
+ if (video_caps & ACPI_VIDEO_BACKLIGHT) {
+ /*
+ * Windows 8 and newer no longer use the ACPI video interface,
+ * so it often does not work. If the ACPI tables are written
+ * for win8 and native brightness ctl is available, use that.
+ *
+ * The native check deliberately is inside the if acpi-video
+ * block on older devices without acpi-video support native
+ * is usually not the best choice.
+ */
+ if (acpi_osi_is_win8() && native_available)
+ return acpi_backlight_native;
+ else
+ return acpi_backlight_video;
+ }
- return acpi_backlight_video;
+ /* No ACPI video (old hw), use vendor specific fw methods. */
+ return acpi_backlight_vendor;
}
enum acpi_backlight_type acpi_video_get_backlight_type(void)