Re: [PATCH v10 2/3] drm/i915: Add option to support dynamic backlight via DPCD

["Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>]

On Fri, 2017-05-26 at 18:42 -0700, Puthikorn Voravootivat wrote:
> This patch adds option to enable dynamic backlight for eDP
> panel that supports this feature via DPCD register and
> set minimum / maximum brightness to 0% and 100% of the
> normal brightness.
> 
> Signed-off-by: Puthikorn Voravootivat <puthik@chromium.org>
> ---
>  drivers/gpu/drm/i915/i915_params.c            |  5 ++++
>  drivers/gpu/drm/i915/i915_params.h            |  3 +-
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 42 ++++++++++++++++++++++-----
>  3 files changed, 41 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 3758ae1f11b4..ce033d58134e 100644
> --- a/drivers/gpu/drm/i915/i915_params.c
> +++ b/drivers/gpu/drm/i915/i915_params.c
> @@ -65,6 +65,7 @@ struct i915_params i915 __read_mostly = {
>  	.inject_load_failure = 0,
>  	.enable_dpcd_backlight = -1,
>  	.enable_gvt = false,
> +	.enable_dbc = false,
>  };
>  
>  module_param_named(modeset, i915.modeset, int, 0400);
> @@ -254,3 +255,7 @@ MODULE_PARM_DESC(enable_dpcd_backlight,
>  module_param_named(enable_gvt, i915.enable_gvt, bool, 0400);
>  MODULE_PARM_DESC(enable_gvt,
>  	"Enable support for Intel GVT-g graphics virtualization host support(default:false)");
> +
> +module_param_named_unsafe(enable_dbc, i915.enable_dbc, bool, 0600);
> +MODULE_PARM_DESC(enable_dbc,
> +	"Enable support for dynamic backlight control (default:false)");
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index ac02efce6e22..2de3e2850b54 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -67,7 +67,8 @@
>  	func(bool, nuclear_pageflip); \
>  	func(bool, enable_dp_mst); \
>  	func(int, enable_dpcd_backlight); \
> -	func(bool, enable_gvt)
> +	func(bool, enable_gvt); \
> +	func(bool, enable_dbc)
>  
>  #define MEMBER(T, member) T member
>  struct i915_params {
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index c89aae804659..f55af41ce3bd 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -100,11 +100,26 @@ 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) };
> +
> +	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_DBC_MINIMUM_BRIGHTNESS_SET,
> +			  dbc, sizeof(dbc)) < 0) {
> +		DRM_DEBUG_KMS("Failed to write aux DBC brightness level\n");
> +	}
> +}
> +
>  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 edp_backlight_mode = 0;
> +	uint8_t dpcd_buf, new_dpcd_buf, edp_backlight_mode;
>  
>  	if (drm_dp_dpcd_readb(&intel_dp->aux,
>  			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
> @@ -113,18 +128,15 @@ 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;
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, dpcd_buf) < 0) {
> -			DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
> -		}
> +		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 */
> @@ -133,6 +145,20 @@ static void intel_dp_aux_enable_backlight(struct intel_connector *connector)
>  		break;
>  	}
>  
> +	if (i915.enable_dbc &&
> +	    (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);
> +		DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> +	}
> +


Just curious, does DBC require DP AUX brightness control? 


-DK

> +	if (new_dpcd_buf != dpcd_buf) {
> +		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> +			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
> +			DRM_DEBUG_KMS("Failed to write aux backlight mode\n");
> +		}
> +	}
> +
>  	set_aux_backlight_enable(intel_dp, true);
>  	intel_dp_aux_set_backlight(connector, connector->panel.backlight.level);
>  }

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