[Intel-gfx] [PATCH] drm/i915: Use AUX for backlight only if eDP 1.4 or later

[Pandiyan, Dhinakaran]

On Thu, 2017-07-20 at 10:06 +0000, Tc, Jenny wrote:
> > >> With older panels, AUX pin for backlight doesn't work.
> > 
> > What evidence do you have to back up that claim?
> 
> Debugging further it's found that the panel I am having doesn't support AUX Backlight.
> 
> cat /sys/kernel/debug/dri/0/eDP-1/i915_dpcd 
> ...
> 0701: bb ff 00 00
> ....
> 
> With below change its working for my panel. But doesn't address issue reported in
> https://bugs.freedesktop.org/show_bug.cgi?id=101619 which seems to have a wrong DPCD data.
> Since we don't have a proper fix for all panels, I agree for revert.
> 
> intel_dp_aux_display_control_heuristic(struct intel_connector *connector)
>         struct intel_dp *intel_dp = enc_to_intel_dp(&connector->encoder->base);
>         uint8_t reg_val;
>  
> +       /* Panel dosn't support enabling AUX Backlight control */
> +       if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)) {
> +               return false;
> +       }

AUX backlight brightness control should work even without AUX enable
capability.


>         /* Panel doesn't support adjusting backlight brightness via PWN pin */
>         if (!(intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
>                 return true;
>  
> > >> On some panels, this causes backlight issues on S3 resume.
> > >
> > > What is it that we are missing in the resume path?
> > >
> > >>  Enable the
> > >> feature only for eDP1.4 or later.
> > >
> > > I can't find the eDP 1.4 requirement in the spec. Regional brightness
> > > control was added in eDP 1.4, but we don't enable that. My concern is
> > > we might be missing a real fix by ignoring < eDP 1.4 panels.
> > 
> > Agreed.
> > 
> > This has been going on too long now, with no real effort to get at the roots of
> > the problem. The right approach is to revert the regressing commits now,
> > and start over. Reverts posted [1].
> > 
> > BR,
> > Jani.
> > 
> > [1] https://patchwork.freedesktop.org/series/27623/
> > 
> > >
> > >
> > >>
> > >> Fix-suggested-by: Puthikorn Voravootivat <puthik at chromium.org>
> > >
> > > 1. Please use the "Fixes" tag to refer to the commit that introduced
> > > the code you are fixing.
> > > 2. The "Suggested-by" tag is more common to give credits to the person
> > > who suggested the fix.
> > > 3. Please use the "Bugzilla" tag to point to the bug that David
> > > reported.
> > >
> > >
> > >> Signed-off-by: Jenny TC <jenny.tc at intel.com>
> > >> ---
> > >>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 6 +++++-
> > >>  1 file changed, 5 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > >> b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > >> index b25cd88..421f31f 100644
> > >> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > >> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > >> @@ -292,7 +292,7 @@ static int intel_dp_aux_setup_backlight(struct
> > intel_connector *connector,
> > >>   * via PWM pin or using AUX is better than using PWM pin.
> > >>   *
> > >>   * The heuristic to determine that using AUX pin is better than
> > >> using PWM pin is
> > >> - * that the panel support any of the feature list here.
> > >> + * that the panel is eDP 1.4 or later and support any of the feature
> > >> + list here
> > >>   * - Regional backlight brightness adjustment
> > >>   * - Backlight PWM frequency set
> > >>   * - More than 8 bits resolution of brightness level @@ -310,6
> > >> +310,10 @@ static int intel_dp_aux_setup_backlight(struct
> > intel_connector *connector,
> > >>  	if (!(intel_dp->edp_dpcd[2] &
> > DP_EDP_BACKLIGHT_BRIGHTNESS_PWM_PIN_CAP))
> > >>  		return true;
> > >>
> > >> +	/* Enable this for eDP 1.4 panel or later. */
> > >> +	if (intel_dp->edp_dpcd[0] < DP_EDP_14)
> > >> +		return false;
> > >> +
> > >>  	/* Panel supports regional backlight brightness adjustment */
> > >>  	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_GENERAL_CAP_3,
> > >>  			      &reg_val) != 1) {
> > 
> > --
> > Jani Nikula, Intel Open Source Technology Center
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