[Intel-gfx] [PATCH v12 3/3] drm/i915: Add option to support dynamic backlight via DPCD

[David Weinehall]

On Thu, Jun 22, 2017 at 12:03:39PM -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.

This patch causes a regression on my ThinkPad X1 Carbon Gen 4;
with enable_dbc = true the backlight stays off; setting i915.enable_dbc=0
on boot makes things work properly again.

> Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>
> Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> ---
>  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 | 26 ++++++++++++++++++++++++++
>  3 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
> index 5b5ab15d191f..88b9d3e6713a 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 = true,
>  };
>  
>  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:true)");
> diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
> index 0d6cf9138dc4..057e203e6bda 100644
> --- a/drivers/gpu/drm/i915/i915_params.h
> +++ b/drivers/gpu/drm/i915/i915_params.h
> @@ -67,7 +67,8 @@
>  	func(bool, verbose_state_checks); \
>  	func(bool, nuclear_pageflip); \
>  	func(bool, enable_dp_mst); \
> -	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 fea161727c6e..b25cd88fc1c5 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -173,6 +173,24 @@ static bool intel_dp_aux_set_pwm_freq(struct intel_connector *connector)
>  	return true;
>  }
>  
> +/*
> +* Set minimum / maximum dynamic brightness percentage. This value is expressed
> +* as the percentage of normal brightness in 5% increments.
> +*/
> +static bool
> +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");
> +		return false;
> +	}
> +	return true;
> +}
> +
>  static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_state,
>  					  const struct drm_connector_state *conn_state)
>  {
> @@ -208,6 +226,14 @@ static void intel_dp_aux_enable_backlight(const struct intel_crtc_state *crtc_st
>  		if (intel_dp_aux_set_pwm_freq(connector))
>  			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
>  
> +	if (i915.enable_dbc &&
> +	    (intel_dp->edp_dpcd[2] & DP_EDP_DYNAMIC_BACKLIGHT_CAP)) {
> +		if(intel_dp_aux_set_dynamic_backlight_percent(intel_dp, 0, 100)) {
> +			new_dpcd_buf |= DP_EDP_DYNAMIC_BACKLIGHT_ENABLE;
> +			DRM_DEBUG_KMS("Enable dynamic brightness.\n");
> +		}
> +	}
> +
>  	if (new_dpcd_buf != dpcd_buf) {
>  		if (drm_dp_dpcd_writeb(&intel_dp->aux,
>  			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
> -- 
> 2.13.1.611.g7e3b11ae1-goog
> 
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