[Intel-gfx] [PATCH v5 2/9] drm/i915: Correctly enable backlight brightness adjustment via DPCD

[Pandiyan, Dhinakaran]

On Wed, 2017-05-03 at 17:28 -0700, Puthikorn Voravootivat wrote:
> intel_dp_aux_enable_backlight() assumed that the register
> BACKLIGHT_BRIGHTNESS_CONTROL_MODE can only has value 01
> (DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET) when initialize.
> 
> This patch fixed that by handling all cases of that register.
> 
> Signed-off-by: Puthikorn Voravootivat <puthik at chromium.org>

Spec says both 0x00 and 0x01 are possible power-on defaults. So,

Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>

> ---
>  drivers/gpu/drm/i915/intel_dp_aux_backlight.c | 33 ++++++++++++++++++++++-----
>  1 file changed, 27 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> index 24a905d1a74b..ad8560c5f689 100644
> --- a/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/intel_dp_aux_backlight.c
> @@ -97,15 +97,36 @@ 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;
>  
>  	set_aux_backlight_enable(intel_dp, true);
>  
> -	if ((drm_dp_dpcd_readb(&intel_dp->aux,
> -			       DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) == 1) &&
> -	    ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> -	     DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET))
> -		drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> -				   (dpcd_buf | DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD));
> +	if (drm_dp_dpcd_readb(&intel_dp->aux,
> +			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
> +		DRM_DEBUG_KMS("Failed to read DPCD register 0x%x\n",
> +			      DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> +		return;
> +	}
> +
> +	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");
> +		}
> +		break;
> +
> +	/* Do nothing when it is already DPCD mode */
> +	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> +	default:
> +		break;
> +	}
>  }
>  
>  static void intel_dp_aux_disable_backlight(struct intel_connector *connector)