i915/dp/fec: Cache the FEC_CAPABLE DPCD register

Similar to DSC DPCD registers, let us cache
FEC_CAPABLE register to avoid using stale
values. With this we can avoid aux reads
everytime and instead read the cached values.

v2: Avoid using memset and array for a single
field. (Manasi,Jani)

v3: Print FEC CAPABILITY value. (Manasi)

Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181102041455.15818-1-anusha.srivatsa@intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -3954,6 +3954,9 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
 	 */
 	memset(intel_dp->dsc_dpcd, 0, sizeof(intel_dp->dsc_dpcd));
 
+	/* Clear fec_capable to avoid using stale values */
+	intel_dp->fec_capable = 0;
+
 	/* Cache the DSC DPCD if eDP or DP rev >= 1.4 */
 	if (intel_dp->dpcd[DP_DPCD_REV] >= 0x14 ||
 	    intel_dp->edp_dpcd[0] >= DP_EDP_14) {
@@ -3966,6 +3969,15 @@ static void intel_dp_get_dsc_sink_cap(struct intel_dp *intel_dp)
 		DRM_DEBUG_KMS("DSC DPCD: %*ph\n",
 			      (int)sizeof(intel_dp->dsc_dpcd),
 			      intel_dp->dsc_dpcd);
+		/* FEC is supported only on DP 1.4 */
+		if (!intel_dp_is_edp(intel_dp)) {
+			if (drm_dp_dpcd_readb(&intel_dp->aux, DP_FEC_CAPABILITY,
+					      &intel_dp->fec_capable) < 0)
+				DRM_ERROR("Failed to read FEC DPCD register\n");
+
+		DRM_DEBUG_KMS("FEC CAPABILITY: %x\n",
+			      intel_dp->fec_capable);
+		}
 	}
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -1114,6 +1114,7 @@ struct intel_dp {
 	uint8_t downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
 	uint8_t edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
 	u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];
+	u8 fec_capable;
 	/* source rates */
 	int num_source_rates;
 	const int *source_rates;