ACPI: video: Prefer native over vendor

[ Upstream commit fb1836c91317e0770950260dfa91eb9b2170cb27 ]

When available prefer native backlight control over vendor backlight
control.

Testing has shown that there are quite a few laptop models which rely
on native backlight control (they don't have ACPI video bus backlight
control) and on which acpi_osi_is_win8() returns false.

Currently __acpi_video_get_backlight_type() returns vendor on these
laptops, leading to an empty /sys/class/backlight.

As a workaround for this acpi_video_backlight_use_native() has been
temporarily changed to always return true.

This re-introduces the problem of having multiple backlight
devices under /sys/class/backlight for a single panel.

Change __acpi_video_get_backlight_type() to prefer native over vendor
when available. So that it returns native on these models.

And change acpi_video_backlight_use_native() back to only return
true when __acpi_video_get_backlight_type() returns native.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 0c17ee9..76b7e7f 100644 (file)
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -795,10 +795,10 @@ static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
                return acpi_backlight_video;
 
        /* Use native if available */
-       if (native_available && prefer_native_over_acpi_video())
+       if (native_available)
                return acpi_backlight_native;
 
-       /* No ACPI video (old hw), use vendor specific fw methods. */
+       /* No ACPI video/native (old hw), use vendor specific fw methods. */
        return acpi_backlight_vendor;
 }
 
@@ -810,18 +810,6 @@ EXPORT_SYMBOL(acpi_video_get_backlight_type);
 
 bool acpi_video_backlight_use_native(void)
 {
-       /*
-        * Call __acpi_video_get_backlight_type() to let it know that
-        * a native backlight is available.
-        */
-       __acpi_video_get_backlight_type(true);
-
-       /*
-        * For now just always return true. There is a whole bunch of laptop
-        * models where (video_caps & ACPI_VIDEO_BACKLIGHT) is false causing
-        * __acpi_video_get_backlight_type() to return vendor, while these
-        * models only have a native backlight control.
-        */
-       return true;
+       return __acpi_video_get_backlight_type(true) == acpi_backlight_native;
 }
 EXPORT_SYMBOL(acpi_video_backlight_use_native);