On Fri, Mar 19, 2021 at 5:31 PM Evan Benn <evanbenn@xxxxxxxxx> wrote: > > On Sat, 20 Mar 2021 at 02:10, Harry Wentland <harry.wentland@xxxxxxx> wrote: > > On 2021-03-19 10:22 a.m., Alex Deucher wrote: > > > On Fri, Mar 19, 2021 at 3:23 AM Evan Benn <evanbenn@xxxxxxxxxxxx> 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 <evanbenn@xxxxxxxxxxxx> > > >> > > >> --- > > >> 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? > > > > > > > Yeah, this is a NACK from me as-is for the reasons Alex described. > > Thanks Harry + Alex, > > I agree this solution is not the best. > > > > > I agree a whitelist approach might be best. > > Do you have any idea what an allowlist could be keyed on? > Is the flickering you observed here a function of the panel or the gpu > or some other component? > Maybe we could move the minimum level into the logic for that hardware. > Maybe the panel string from the EDID? Either that or something from dmi data? Harry would probably have a better idea. Alex > > > > Is this fix perhaps for OLED panels? If so we could use a different > > min-value for OLED panels that don't do PWM, but use 12 for everything else. > > All the chromebooks I have worked with LCD + LED backlight have been > fine with a backlight set to 0. > We do have OLED panels too, but I'm not aware of what they do. > > > Harry > > > > > 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-devel@xxxxxxxxxxxxxxxxxxxxx > > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel>> _______________________________________________ > > > dri-devel mailing list > > > dri-devel@xxxxxxxxxxxxxxxxxxxxx > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel>> > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
