ACPI: video: Stop trying to use vendor backlight control on laptops from after ~2012

[linux-2.6-microblaze.git] / drivers / acpi / video_detect.c

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index b87783c..eb014c0 100644 (file)
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -844,6 +844,27 @@ enum acpi_backlight_type __acpi_video_get_backlight_type(bool native, bool *auto
        if (native_available)
                return acpi_backlight_native;
 
+       /*
+        * The vendor specific BIOS interfaces are only necessary for
+        * laptops from before ~2008.
+        *
+        * For laptops from ~2008 till ~2023 this point is never reached
+        * because on those (video_caps & ACPI_VIDEO_BACKLIGHT) above is true.
+        *
+        * Laptops from after ~2023 no longer support ACPI_VIDEO_BACKLIGHT,
+        * if this point is reached on those, this likely means that
+        * the GPU kms driver which sets native_available has not loaded yet.
+        *
+        * Returning acpi_backlight_vendor in this case is known to sometimes
+        * cause a non working vendor specific /sys/class/backlight device to
+        * get registered.
+        *
+        * Return acpi_backlight_none on laptops with ACPI tables written
+        * for Windows 8 (laptops from after ~2012) to avoid this problem.
+        */
+       if (acpi_osi_is_win8())
+               return acpi_backlight_none;
+
        /* No ACPI video/native (old hw), use vendor specific fw methods. */
        return acpi_backlight_vendor;
 }