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

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Date:   Wed, 07 Oct 2020 17:53:21 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Satadru Pramanik <satadru@...il.com>,
        Kai-Heng Feng <kai.heng.feng@...onical.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

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.


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