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

[Anusha Srivatsa]

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