drm/i915: Force sink crc stop before start.

By Vesa DP spec, test counter at DP_TEST_SINK_MISC just reset to 0
when unsetting DP_TEST_SINK_START, so let's force this stop here.

But let's minimize the aux transactions and just do it when we know
it hasn't been properly stoped.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -3995,29 +3995,44 @@ intel_dp_probe_mst(struct intel_dp *intel_dp)
 	return intel_dp->is_mst;
 }
 
-static void intel_dp_sink_crc_stop(struct intel_dp *intel_dp)
+static int intel_dp_sink_crc_stop(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct intel_crtc *intel_crtc = to_intel_crtc(dig_port->base.base.crtc);
 	u8 buf;
+	int ret = 0;
 
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK, &buf) < 0) {
 		DRM_DEBUG_KMS("Sink CRC couldn't be stopped properly\n");
-		return;
+		ret = -EIO;
+		goto out;
 	}
 
 	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_TEST_SINK,
-			       buf & ~DP_TEST_SINK_START) < 0)
+			       buf & ~DP_TEST_SINK_START) < 0) {
 		DRM_DEBUG_KMS("Sink CRC couldn't be stopped properly\n");
+		ret = -EIO;
+		goto out;
+	}
 
+	intel_dp->sink_crc_started = false;
+ out:
 	hsw_enable_ips(intel_crtc);
+	return ret;
 }
 
 static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
 	struct intel_crtc *intel_crtc = to_intel_crtc(dig_port->base.base.crtc);
 	u8 buf;
+	int ret;
+
+	if (intel_dp->sink_crc_started) {
+		ret = intel_dp_sink_crc_stop(intel_dp);
+		if (ret)
+			return ret;
+	}
 
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, &buf) < 0)
 		return -EIO;
@@ -4036,6 +4051,7 @@ static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
 		return -EIO;
 	}
 
+	intel_dp->sink_crc_started = true;
 	return 0;
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -713,6 +713,7 @@ struct intel_dp {
 	/* sink rates as reported by DP_SUPPORTED_LINK_RATES */
 	uint8_t num_sink_rates;
 	int sink_rates[DP_MAX_SUPPORTED_RATES];
+	bool sink_crc_started;
 	struct drm_dp_aux aux;
 	uint8_t train_set[4];
 	int panel_power_up_delay;