On Fri, Mar 19, 2021 at 3:23 AM Evan Benn <evanb...@chromium.org> wrote: > > AMDGPU_DM_DEFAULT_MIN_BACKLIGHT was set to the value of 12 > to ensure no display backlight will flicker at low user brightness > settings. However this value is quite bright, so for devices that do not > implement the ACPI ATIF > ATIF_FUNCTION_QUERY_BRIGHTNESS_TRANSFER_CHARACTERISTICS > functionality the user cannot set the brightness to a low level even if > the display would support such a low PWM. > > This ATIF feature is not implemented on for example AMD grunt chromebooks. > > Signed-off-by: Evan Benn <evanb...@chromium.org> > > --- > I could not find a justification for the reason for the value. It has > caused some noticable regression for users: > https://bugzilla.kernel.org/show_bug.cgi?id=203439 > > Maybe this can be either user controlled or userspace configured, but > preventing users from turning their backlight dim seems wrong.
My understanding is that some panels flicker if you set the min to a value too low. This was a safe minimum if the platform didn't specify it's own safe minimum. I think we'd just be trading one bug for another (flickering vs not dim enough). Maybe a whitelist or blacklist would be a better solution? Alex > > Also reviewed here: > https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2748377 > > drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > index 573cf17262da..0129bd69b94e 100644 > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c > @@ -3151,7 +3151,7 @@ static int amdgpu_dm_mode_config_init(struct > amdgpu_device *adev) > return 0; > } > > -#define AMDGPU_DM_DEFAULT_MIN_BACKLIGHT 12 > +#define AMDGPU_DM_DEFAULT_MIN_BACKLIGHT 0 > #define AMDGPU_DM_DEFAULT_MAX_BACKLIGHT 255 > #define AUX_BL_DEFAULT_TRANSITION_TIME_MS 50 > > -- > 2.31.0.291.g576ba9dcdaf-goog > > _______________________________________________ > dri-devel mailing list > dri-de...@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
