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

[Puthikorn Voravootivat <puthik@xxxxxxxxxxxx>]

On Tue, May 2, 2017 at 8:00 PM, Pandiyan, Dhinakaran <dhinakaran.pandiyan@xxxxxxxxx> 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@xxxxxxxxxxxx>
> ---
>  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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