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

[Pandiyan, Dhinakaran]

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. 


> 
> 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.

-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)