[PATCH 1/2] drm/amd/display: Fix the brightness read via aux

[Takashi Iwai]

On Fri, 05 Feb 2021 17:36:44 +0100,
Alex Deucher wrote:
> 
> On Wed, Feb 3, 2021 at 7:42 AM Takashi Iwai <tiwai at suse.de> wrote:
> >
> > The current code tries to read the brightness value via
> > dc_link_get_backlight_level() no matter whether it's controlled via
> > aux or not, and this results in a bogus value returned.
> > Fix it to read the current value via
> > dc_link_get_backlight_level_nits() for the aux.
> >
> > BugLink: https://bugzilla.opensuse.org/show_bug.cgi?id=1180749
> > BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1438
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> 
> This looks fine to me.  FWIW, I have a similar patch set here:
> https://cgit.freedesktop.org/~agd5f/linux/log/?h=backlight_wip

I'm fine to scratch mine as long as the issue gets fixed :)

FWIW, the biggest problem so far was the aux channel backlight didn't
work as expected, the actual backlight isn't changed by the backlight
sysfs write.  (And the sysfs read gives a bogus value, but it's not
the cause of the non-working backlight control.)

Does the aux channel backlight really work with the current code?
Or is this rather a device-specific issue (e.g. broken BIOS) and we
might need to come up with a deny list or such?


thanks,

Takashi