[Intel-gfx] [v4 3/7] i915/dp/fec: Check for FEC Support

[Ville Syrjälä]

On Tue, Oct 30, 2018 at 05:45:13PM -0700, Anusha Srivatsa wrote:
> For DP 1.4 and above, Display Stream compression can be
> enabled only if Forward Error Correctin can be performed.
> 
> Check if the sink supports FEC using the helper.
> 
> v2: Mention External DP where ever FEC is mentioned
> in the code.Check return status of dpcd reads. (Gaurav)
> - Do regular mode check even if FEC is not supported. (manasi)
> 
> v3: Do not perform any dpcd writes in the atomic
> check phase. (DK, Manasi)
> 
> v4: Use debug level logging for scenario where sink does
> not support a feature. (DK)
> 
> v5: Correct commit message. rebase.
> 
> v6: pass single field instead of an array for helper
> function. (manasi)
> 
> Cc: Gaurav K Singh <gaurav.k.singh at intel.com>
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Manasi Navare <manasi.d.navare at intel.com>
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> Signed-off-by: Anusha Srivatsa <anusha.srivatsa at intel.com>
> Reviewed-by: Manasi Navare <manasi.d.navare at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_dp.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 8ae7cf3d4ee1..a344be555dd6 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -680,7 +680,7 @@ intel_dp_mode_valid(struct drm_connector *connector,
>  			dsc_slice_count =
>  				drm_dp_dsc_sink_max_slice_count(intel_dp->dsc_dpcd,
>  								true);
> -		} else {
> +		} else if (drm_dp_sink_supports_fec(intel_dp->fec_capable)) {
>  			dsc_max_output_bpp =
>  				intel_dp_dsc_get_output_bpp(max_link_clock,
>  							    max_lanes,
> @@ -690,7 +690,8 @@ intel_dp_mode_valid(struct drm_connector *connector,
>  				intel_dp_dsc_get_slice_count(intel_dp,
>  							     target_clock,
>  							     mode->hdisplay);
> -		}
> +		} else
> +			DRM_DEBUG_KMS("Sink device does not Support FEC\n");

Please no debug prints in the mode_valid() that would spam a lot.

Not enough context in the patch for me to see what happens if FEC isn't
supported. Do we just check against the uncompressed limits?

>  	}
>  
>  	if ((mode_rate > max_rate && !(dsc_max_output_bpp && dsc_slice_count)) ||
> @@ -2063,6 +2064,13 @@ static bool intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
>  	if (pipe == PIPE_A && !intel_dp_is_edp(intel_dp))
>  		return false;
>  
> +	/* DSC not supported if external DP sink does not support FEC */
> +	if (!intel_dp_is_edp(intel_dp) &&
> +	    !drm_dp_sink_supports_fec(intel_dp->fec_capable)) {

Why aren't we checking the source capabilities here as well?

> +		DRM_DEBUG_KMS("Sink does not support Forward Error Correction, disabling Display Compression\n");

"disabling Display Compression" is not true. We're rejecting the entire
thing.

> +		return false;
> +	}
> +
>  	/* DSC not supported for DSC sink BPC < 8 */
>  	if (limits->max_bpp < 3 * DP_DSC_MIN_SUPPORTED_BPC) {
>  		DRM_DEBUG_KMS("No DSC support for less than 8bpc\n");
> -- 
> 2.17.1

-- 
Ville Syrjälä
Intel