Re: [PATCH] drm/i915/dp: fall back to 18 bpp when sink capability is unknown

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jan 13, 2016 at 04:35:20PM +0200, Jani Nikula wrote:
> Per DP spec, the source device should fall back to 18 bpp, VESA range
> RGB when the sink capability is unknown. Fix the color depth
> clamping. 18 bpp color depth should ensure full color range in automatic
> mode.
> 
> The clamping has been HDMI specific since its introduction in
> 
> commit 996a2239f93b03c5972923f04b097f65565c5bed
> Author: Daniel Vetter <daniel.vetter@ffwll.ch>
> Date:   Fri Apr 19 11:24:34 2013 +0200
> 
>     drm/i915: Disable high-bpc on pre-1.4 EDID screens
> 
> Cc: stable@vger.kernel.org
> Reported-by: Dihan Wickremasuriya <nayomal@gmail.com>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=105331
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Makes sense to me as far as the spec is concerned.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/intel_display.c | 20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 07ca19b0ec17..6eaecd9385ab 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -12171,11 +12171,21 @@ connected_sink_compute_bpp(struct intel_connector *connector,
>  		pipe_config->pipe_bpp = connector->base.display_info.bpc*3;
>  	}
>  
> -	/* Clamp bpp to 8 on screens without EDID 1.4 */
> -	if (connector->base.display_info.bpc == 0 && bpp > 24) {
> -		DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of 24\n",
> -			      bpp);
> -		pipe_config->pipe_bpp = 24;
> +	/* Clamp bpp to default limit on screens without EDID 1.4 */
> +	if (connector->base.display_info.bpc == 0) {
> +		int type = connector->base.connector_type;
> +		int clamp_bpp = 24;
> +
> +		/* Fall back to 18 bpp when DP sink capability is unknown. */
> +		if (type == DRM_MODE_CONNECTOR_DisplayPort ||
> +		    type == DRM_MODE_CONNECTOR_eDP)
> +			clamp_bpp = 18;
> +
> +		if (bpp > clamp_bpp) {
> +			DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of %d\n",
> +				      bpp, clamp_bpp);
> +			pipe_config->pipe_bpp = clamp_bpp;
> +		}
>  	}
>  }
>  
> -- 
> 2.1.4

-- 
Ville Syrjälä
Intel OTC
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