[PATCH] drm/i915/dp: Read link status more times when EQ not done

["Lee, Shawn C" <shawn.c.lee@intel.com>]

From: "Lee, Shawn C" <shawn.c.lee@intel.com>

When user space link status, display driver read DPCD register
0x202, 0x203 and 0x204 to identify sink status. When PSR exit
is ongoing before EQ done. Panel will report EQ & symbol lock
not done. Both of them are under progressing at the same time
to cause this issue.

This WA try to read link status more times if EQ not done.
Panel spec request at least 1000us for fast link train when
PSR exit. So driver will wait 1000us~1500us then retrieve
sink link status again.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99639
TEST=Reboot DUT and no flicking on local display at login screen

Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: Wei Shun Chen <wei.shun.chang@intel.com>
Cc: Gary C Wang <gary.c.wang@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>

Signed-off-by: Lee, Shawn C <shawn.c.lee@intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c |   33 ++++++++++++++++++++++++++++-----
 1 file changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index e80d620846c8..a9a6ce476438 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4136,13 +4136,36 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
 		return;
 
 	/* if link training is requested we should perform it always */
-	if ((intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) ||
-	    (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))) {
-		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
-			      intel_encoder->base.name);
+	if (intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) {
+		DRM_DEBUG_KMS("%s: compliance test mode, retraining\n",
+			intel_encoder->base.name);
+	} else {
+		u8 retry;
+
+		for (retry = 0; retry < 3; retry++) {
+			if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
+				/*
+				 * EQ not ok may caused by fast link train while exit PSR active,
+				 * wait at least 1000 us then read it again.
+				 */
+				DRM_DEBUG_KMS("%s: channel EQ not ok, retry = %d, DPCD 0x202 = 0x%x, 0x203 = 0x%x, 0x204 = 0x%x\n",
+					intel_encoder->base.name, retry, link_status[0], link_status[1], link_status[2]);
+				usleep_range(1000, 1500);
+				if (!intel_dp_get_link_status(intel_dp, link_status)) {
+					DRM_ERROR("Failed to get link status\n");
+					return;
+				}
+			} else {
+				/* channel EQ is fine */
+				return;
+			}
+		}
 
-		intel_dp_retrain_link(intel_dp);
+		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
+			intel_encoder->base.name);
 	}
+
+	intel_dp_retrain_link(intel_dp);
 }
 
 /*
-- 
1.7.9.5

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