[RFC 2/2] ACPI: video: Prefer native over vendor

Hans de Goede
2022-11-05T14:54:14Z

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>
---
drivers/acpi/video_detect.c | 18 +++---------------
1 file changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index ec7421a3986f..19e9bc25225d 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -748,10 +748,10 @@ 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;
}

@@ -763,18 +763,6 @@ 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);
--
2.37.3