linux-kernel - Re: [PATCH 1/2] drm/i915/dpcd_bl: Skip testing control capability with force DPCD quirk

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Message-ID: <c06193df9273fb396bdb40e73aed64197ba3b01d.camel@redhat.com>
Date:   Thu, 08 Oct 2020 12:39:30 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Satadru Pramanik <satadru@...il.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Juha-Pekka Heikkila <juhapekka.heikkila@...il.com>,
        intel-gfx@...ts.freedesktop.org,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/i915/dpcd_bl: Skip testing control capability
 with force DPCD quirk

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@...hat.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?\

Not yet - we need someone to help with reviewing my Intel HDR backlight
interface patches before we can drop that. I was just talking about dropping the
check where we don't enable the DPCD backlight if it claims to support
DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP

> 
> 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@...onical.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