drm/i915: Save latest known sink CRC to compensate delayed counter reset.

By Vesa DP 1.2 Spec TEST_CRC_COUNT should be
"reset to 0 when TEST_SINK bit 0 = 0."

However for some strange reason when PSR is enabled in
certain platforms this is not true. At least not immediatelly.

So we face cases like this:

first get_sink_crc operation:
	     count: 0, crc: 000000000000
	     count: 1, crc: c101c101c101
returned expected crc: c101c101c101

secont get_sink_crc operation:
	     count: 1, crc: c101c101c101
	     count: 0, crc: 000000000000
	     count: 1, crc: 0000c1010000
should return expected crc: 0000c1010000

But also the reset to 0 should be faster resulting into:

get_sink_crc operation:
	     count: 1, crc: c101c101c101
	     count: 1, crc: 0000c1010000
should return expected crc: 0000c1010000

So in order to know that the second one is valid one
we need to compare the pair (count, crc) with latest (count, crc).

If the pair changed you have your valid CRC.
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

@@ -4015,7 +4015,7 @@ static int intel_dp_sink_crc_stop(struct intel_dp *intel_dp)
 		goto out;
 	}
 
-	intel_dp->sink_crc_started = false;
+	intel_dp->sink_crc.started = false;
  out:
 	hsw_enable_ips(intel_crtc);
 	return ret;
@@ -4028,7 +4028,7 @@ static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
 	u8 buf;
 	int ret;
 
-	if (intel_dp->sink_crc_started) {
+	if (intel_dp->sink_crc.started) {
 		ret = intel_dp_sink_crc_stop(intel_dp);
 		if (ret)
 			return ret;
@@ -4040,6 +4040,8 @@ static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
 	if (!(buf & DP_TEST_CRC_SUPPORTED))
 		return -ENOTTY;
 
+	intel_dp->sink_crc.last_count = buf & DP_TEST_COUNT_MASK;
+
 	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK, &buf) < 0)
 		return -EIO;
 
@@ -4051,7 +4053,7 @@ static int intel_dp_sink_crc_start(struct intel_dp *intel_dp)
 		return -EIO;
 	}
 
-	intel_dp->sink_crc_started = true;
+	intel_dp->sink_crc.started = true;
 	return 0;
 }
 
@@ -4061,29 +4063,39 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 	struct drm_device *dev = dig_port->base.base.dev;
 	struct intel_crtc *intel_crtc = to_intel_crtc(dig_port->base.base.crtc);
 	u8 buf;
-	int test_crc_count;
+	int count, ret;
 	int attempts = 6;
-	int ret;
 
 	ret = intel_dp_sink_crc_start(intel_dp);
 	if (ret)
 		return ret;
 
-	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, &buf) < 0) {
-		ret = -EIO;
-		goto stop;
-	}
-
-	test_crc_count = buf & DP_TEST_COUNT_MASK;
-
 	do {
+		intel_wait_for_vblank(dev, intel_crtc->pipe);
+
 		if (drm_dp_dpcd_readb(&intel_dp->aux,
 				      DP_TEST_SINK_MISC, &buf) < 0) {
 			ret = -EIO;
 			goto stop;
 		}
-		intel_wait_for_vblank(dev, intel_crtc->pipe);
-	} while (--attempts && (buf & DP_TEST_COUNT_MASK) == test_crc_count);
+		count = buf & DP_TEST_COUNT_MASK;
+		/*
+		 * Count might be reset during the loop. In this case
+		 * last known count needs to be reset as well.
+		 */
+		if (count == 0)
+			intel_dp->sink_crc.last_count = 0;
+
+		if (drm_dp_dpcd_read(&intel_dp->aux, DP_TEST_CRC_R_CR, crc, 6) < 0) {
+			ret = -EIO;
+			goto stop;
+		}
+	} while (--attempts && (count == 0 || (count == intel_dp->sink_crc.last_count &&
+					       !memcmp(intel_dp->sink_crc.last_crc, crc,
+						       6 * sizeof(u8)))));
+
+	intel_dp->sink_crc.last_count = buf & DP_TEST_COUNT_MASK;
+	memcpy(intel_dp->sink_crc.last_crc, crc, 6 * sizeof(u8));
 
 	if (attempts == 0) {
 		DRM_DEBUG_KMS("Panel is unable to calculate CRC after 6 vblanks\n");
@@ -4091,8 +4103,6 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 		goto stop;
 	}
 
-	if (drm_dp_dpcd_read(&intel_dp->aux, DP_TEST_CRC_R_CR, crc, 6) < 0)
-		ret = -EIO;
 stop:
 	intel_dp_sink_crc_stop(intel_dp);
 	return ret;

drivers/gpu/drm/i915/intel_drv.h

@@ -696,6 +696,12 @@ enum link_m_n_set {
 	M2_N2
 };
 
+struct sink_crc {
+	bool started;
+	u8 last_crc[6];
+	int last_count;
+};
+
 struct intel_dp {
 	uint32_t output_reg;
 	uint32_t aux_ch_ctl_reg;
@@ -713,7 +719,7 @@ 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 sink_crc sink_crc;
 	struct drm_dp_aux aux;
 	uint8_t train_set[4];
 	int panel_power_up_delay;