[Intel-gfx] [PATCH RESEND v4 3/6] drm/i915: Support dynamic backlight via DPCD register

[Puthikorn Voravootivat]

On Tue, May 2, 2017 at 8:00 PM, Pandiyan, Dhinakaran <
dhinakaran.pandiyan at intel.com> wrote:

> On Tue, 2017-04-18 at 16:48 -0700, Puthikorn Voravootivat wrote:
> > This patch enables dynamic backlight by default for eDP
> > panel that supports this feature via DPCD register and
> > set minimum / maximum brightness to 0% and 100% of the
> > normal brightness.
>
>
> What does dynamic backlight do? I am trying to understand what allowing
> 0% minimum brightness means.
>
> Display will make backlight dimmer when content shown on screen is darker.
See
https://www.ecnmag.com/article/2010/04/content-adaptive-lcd-backlight-control

>
> >
> > Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> > ---
> >  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 31
> +++++++++++++++++++++++----
> >  1 file changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > index f06c8381c74e..ae1b6fe67feb 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> > @@ -97,10 +97,24 @@ intel_dp_aux_set_backlight(struct intel_connector
> *connector, u32 level)
> >       }
> >  }
> >
> > +/*
> > + * Set minimum / maximum dynamic brightness percentage. This value is
> expressed
> > + * as the percentage of normal brightness in 5% increments.
> > + */
> > +static void
> > +intel_dp_aux_set_dynamic_backlight_percent(struct intel_dp *intel_dp,
> > +                                        u32 min, u32 max)
> > +{
> > +     u8 dbc[] = { DIV_ROUND_CLOSEST(min, 5), DIV_ROUND_CLOSEST(max, 5)
> };
> > +     drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_DBC_MINIMUM_BRIGHTNESS_
> SET,
> > +                       dbc, sizeof(dbc));
> > +}
> > +
> >  static void intel_dp_aux_enable_backlight(struct intel_connector
> *connector)
> >  {
> >       struct intel_dp *intel_dp = enc_to_intel_dp(&connector->
> encoder->base);
> >       uint8_t dpcd_buf = 0;
> > +     uint8_t new_dpcd_buf = 0;
> >       uint8_t edp_backlight_mode = 0;
> >
> >       set_aux_backlight_enable(intel_dp, true);
> > @@ -110,16 +124,15 @@ static void intel_dp_aux_enable_backlight(struct
> intel_connector *connector)
> >               return;
> >       }
> >
> > +     new_dpcd_buf = dpcd_buf;
> >       edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_
> MASK;
> >
> >       switch (edp_backlight_mode) {
> >       case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> >       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> >       case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> > -             dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > -             dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> > -             drm_dp_dpcd_writeb(&intel_dp->aux,
> > -                     DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf);
> > +             new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> > +             new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> >               break;
> >
> >       /* Do nothing when it is already DPCD mode */
> > @@ -127,6 +140,16 @@ static void intel_dp_aux_enable_backlight(struct
> intel_connector *connector)
> >       default:
> >               break;
> >       }
>
>
> Still need a switch here? You are setting mode as
> DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD for all four values of mode.
>
>
>
> > +
> > +     if (intel_dp->edp_dpcd[2] & DP_EDP_DYNAMIC_BACKLIGHT_CAP) {
> > +             new_dpcd_buf |= DP_EDP_DYNAMIC_BACKLIGHT_ENABLE;
> > +             intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0,
> 100);
> > +     }
>
> Should enabling dynamic backlight control be logged in debug messages?
> Could be useful in case this turns out to be buggy.
>
Sure

>
> -DK
>
> > +
> > +     if (new_dpcd_buf != dpcd_buf) {
> > +             drm_dp_dpcd_writeb(&intel_dp->aux,
> > +                     DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> > +     }
> >  }
> >
> >  static void intel_dp_aux_disable_backlight(struct intel_connector
> *connector)
>
>
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