Kevin Chowski said he would be geting to working on upstreaming a version
of that which was in the ChromeOS tree here:

https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2344844
when I last spoke to hi

(This was two weeks ago.)

Kevin - do you have any input on this?

Satadru

On Thu, Oct 8, 2020 at 1:07 PM Lyude Paul <lyude@redhat.com> wrote:

> oh hold on, I misspoke. Here's the patch I was thinking of:
>
> https://patchwork.freedesktop.org/series/82041/
>
> On Thu, 2020-10-08 at 10:32 +0800, Kai-Heng Feng wrote:
> > Hi Lyude,
> >
> > > On Oct 8, 2020, at 05:53, Lyude Paul <lyude@redhat.com> wrote:
> > >
> > > Hi! I thought this patch rang a bell, we actually already had some
> > > discussion
> > > about this since there's a couple of other systems this was causing
> issues
> > > for.
> > > Unfortunately it never seems like that patch got sent out. Satadru?
> > >
> > > (if I don't hear back from them soon, I'll just send out a patch for
> this
> > > myself)
> > >
> > > JFYI - the proper fix here is to just drop the
> > > DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP check from the code entirely.
> As
> > > long as
> > > the backlight supports AUX_SET_CAP, that should be enough for us to
> control
> > > it.
> >
> > Does the proper fix include dropping DP_QUIRK_FORCE_DPCD_BACKLIGHT
> entirely?
> >
> > Kai-Heng
> >
> > >
> > > On Wed, 2020-10-07 at 14:58 +0800, Kai-Heng Feng wrote:
> > > > HP DreamColor panel needs to be controlled via AUX interface.
> However,
> > > > it has both DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP and
> > > > DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP set, so it fails to pass
> > > > intel_dp_aux_display_control_capable() test.
> > > >
> > > > Skip the test if the panel has force DPCD quirk.
> > > >
> > > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> > > > ---
> > > > drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 10 ++++++----
> > > > 1 file changed, 6 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > > index acbd7eb66cbe..acf2e1c65290 100644
> > > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > > @@ -347,9 +347,13 @@ int intel_dp_aux_init_backlight_funcs(struct
> > > > intel_connector *intel_connector)
> > > >   struct intel_panel *panel = &intel_connector->panel;
> > > >   struct intel_dp *intel_dp =
> enc_to_intel_dp(intel_connector->encoder);
> > > >   struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> > > > + bool force_dpcd;
> > > > +
> > > > + force_dpcd = drm_dp_has_quirk(&intel_dp->desc,
> intel_dp->edid_quirks,
> > > > +                               DP_QUIRK_FORCE_DPCD_BACKLIGHT);
> > > >
> > > >   if (i915->params.enable_dpcd_backlight == 0 ||
> > > > -     !intel_dp_aux_display_control_capable(intel_connector))
> > > > +     (!force_dpcd &&
> > > > !intel_dp_aux_display_control_capable(intel_connector)))
> > > >           return -ENODEV;
> > > >
> > > >   /*
> > > > @@ -358,9 +362,7 @@ int intel_dp_aux_init_backlight_funcs(struct
> > > > intel_connector *intel_connector)
> > > >    */
> > > >   if (i915->vbt.backlight.type !=
> > > >       INTEL_BACKLIGHT_VESA_EDP_AUX_INTERFACE &&
> > > > -     i915->params.enable_dpcd_backlight != 1 &&
> > > > -     !drm_dp_has_quirk(&intel_dp->desc, intel_dp->edid_quirks,
> > > > -                       DP_QUIRK_FORCE_DPCD_BACKLIGHT)) {
> > > > +     i915->params.enable_dpcd_backlight != 1 && !force_dpcd) {
> > > >           drm_info(&i915->drm,
> > > >                    "Panel advertises DPCD backlight support, but "
> > > >                    "VBT disagrees. If your backlight controls "
> > > --
> > > Sincerely,
> > >      Lyude Paul (she/her)
> > >      Software Engineer at Red Hat
> --
> Sincerely,
>       Lyude Paul (she/her)
>       Software Engineer at Red Hat
>
>