i915/display/dp: SDP CRC16 for 128b132b link layer

Enable SDP error detection configuration, this will set CRC16 in
128b/132b link layer.
For Display version 13 a hardware bit31 in register VIDEO_DIP_CTL is
added to enable/disable SDP CRC applicable for DP2.0 only, but the
default value of this bit will enable CRC16 in 128b/132b hence
skipping this write.
Corrective actions on SDP corruption is yet to be defined.

v2: Moved the CRC enable to link training init(Jani N)
v3: Moved crc enable to ddi pre enable <Jani N>
v4: Separate function for SDP CRC16 (Jani N)
Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230302081532.765821-3-arun.r.murthy@intel.com

drivers/gpu/drm/i915/display/intel_ddi.c

@@ -2519,6 +2519,10 @@ static void intel_ddi_pre_enable_dp(struct intel_atomic_state *state,
 {
 	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 
+	if (HAS_DP20(dev_priv))
+		intel_dp_128b132b_sdp_crc16(enc_to_intel_dp(encoder),
+					    crtc_state);
+
 	if (DISPLAY_VER(dev_priv) >= 12)
 		tgl_ddi_pre_enable_dp(state, encoder, crtc_state, conn_state);
 	else

drivers/gpu/drm/i915/display/intel_dp_link_training.c

@@ -1474,3 +1474,23 @@ void intel_dp_start_link_train(struct intel_dp *intel_dp,
 	if (!passed)
 		intel_dp_schedule_fallback_link_training(intel_dp, crtc_state);
 }
+
+void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
+				 const struct intel_crtc_state *crtc_state)
+{
+	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+
+	/*
+	 * VIDEO_DIP_CTL register bit 31 should be set to '0' to not
+	 * disable SDP CRC. This is applicable for Display version 13.
+	 * Default value of bit 31 is '0' hence discarding the write
+	 * TODO: Corrective actions on SDP corruption yet to be defined
+	 */
+	if (intel_dp_is_uhbr(crtc_state))
+		/* DP v2.0 SCR on SDP CRC16 for 128b/132b Link Layer */
+		drm_dp_dpcd_writeb(&intel_dp->aux,
+				   DP_SDP_ERROR_DETECTION_CONFIGURATION,
+				   DP_SDP_CRC16_128B132B_EN);
+
+	drm_dbg_kms(&i915->drm, "DP2.0 SDP CRC16 for 128b/132b enabled\n");
+}

drivers/gpu/drm/i915/display/intel_dp_link_training.h

@@ -39,4 +39,6 @@ static inline u8 intel_dp_training_pattern_symbol(u8 pattern)
 	return pattern & ~DP_LINK_SCRAMBLING_DISABLE;
 }
 
+void intel_dp_128b132b_sdp_crc16(struct intel_dp *intel_dp,
+				 const struct intel_crtc_state *crtc_state);
 #endif /* __INTEL_DP_LINK_TRAINING_H__ */