drm/i915: Fix Sink CRC

In some cases like when PSR just got enabled the panel need more vblank
times to calculate CRC. I figured that out with the new PSR test cases
facing some cases that I had a green screen but a blank CRC. Even with
2 vblank waits on kernel + 2 vblank waits on test case.

So let's give up to 6 vblank wait time. However we now check for
TEST_CRC_COUNT that shows when panel finished to calculate CRC and
has it ready.

v2: Jani pointed out attempts decrements was wrong and should never reach
the error condition. And Daniel pointed out that EIO is more appropriated than
EGAIN. Also I realized that I have to read test_crc_count after setting
test_sink

v3: Rebase and adding error message

Cc: Todd Previte <tprevite@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Todd Previte <tprevite@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -3807,21 +3807,32 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc)
 	struct drm_device *dev = intel_dig_port->base.base.dev;
 	struct intel_crtc *intel_crtc =
 		to_intel_crtc(intel_dig_port->base.base.crtc);
-	u8 buf[1];
+	u8 buf;
+	int test_crc_count;
+	int attempts = 6;
 
-	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, buf) < 0)
+	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, &buf) < 0)
 		return -EIO;
 
-	if (!(buf[0] & DP_TEST_CRC_SUPPORTED))
+	if (!(buf & DP_TEST_CRC_SUPPORTED))
 		return -ENOTTY;
 
 	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_TEST_SINK,
 			       DP_TEST_SINK_START) < 0)
 		return -EIO;
 
-	/* Wait 2 vblanks to be sure we will have the correct CRC value */
-	intel_wait_for_vblank(dev, intel_crtc->pipe);
+	drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, &buf);
+	test_crc_count = buf & DP_TEST_COUNT_MASK;
+
+	do {
+		drm_dp_dpcd_readb(&intel_dp->aux, DP_TEST_SINK_MISC, &buf);
 		intel_wait_for_vblank(dev, intel_crtc->pipe);
+	} while (--attempts && (buf & DP_TEST_COUNT_MASK) == test_crc_count);
+
+	if (attempts == 0) {
+		DRM_ERROR("Panel is unable to calculate CRC after 6 vblanks\n");
+		return -EIO;
+	}
 
 	if (drm_dp_dpcd_read(&intel_dp->aux, DP_TEST_CRC_R_CR, crc, 6) < 0)
 		return -EIO;

include/drm/drm_dp_helper.h

@@ -303,7 +303,8 @@
 #define DP_TEST_CRC_B_CB		    0x244
 
 #define DP_TEST_SINK_MISC		    0x246
-#define DP_TEST_CRC_SUPPORTED		    (1 << 5)
+# define DP_TEST_CRC_SUPPORTED		    (1 << 5)
+# define DP_TEST_COUNT_MASK		    0x7
 
 #define DP_TEST_RESPONSE		    0x260
 # define DP_TEST_ACK			    (1 << 0)
@@ -313,7 +314,7 @@
 #define DP_TEST_EDID_CHECKSUM		    0x261
 
 #define DP_TEST_SINK			    0x270
-#define DP_TEST_SINK_START	    (1 << 0)
+# define DP_TEST_SINK_START		    (1 << 0)
 
 #define DP_PAYLOAD_TABLE_UPDATE_STATUS      0x2c0   /* 1.2 MST */
 # define DP_PAYLOAD_TABLE_UPDATED           (1 << 0)