[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>

Display driver read DPCD register 0x202, 0x203 and 0x204 to identify
eDP sink status.If PSR exit is ongoing at eDP sink, and eDP source
read these registers at the same time. Panel will report EQ & symbol
lock not done. It will cause panel display flicking.

Try to read link status more times if eDP EQ not done. Panel side
request at least 1000us for fast link train while doing PSR exit.
So wait more than 1000us then retrieve sink's 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 |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 024798a9c016..f6229d616971 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4225,6 +4225,7 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
 {
 	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 
 	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
@@ -4247,6 +4248,27 @@ static void intel_dp_handle_test_request(struct intel_dp *intel_dp)
 
 	/* Retrain if Channel EQ or CR not ok */
 	if (!drm_dp_channel_eq_ok(link_status, intel_dp->lane_count)) {
+		if (is_edp(intel_dp) && dev_priv->psr.enabled) {
+			u8 retry;
+
+			for (retry = 0; retry < 3; retry++) {
+				/*
+				 * 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;
+				}
+
+				if (drm_dp_channel_eq_ok(link_status, intel_dp->lane_count))
+					return;
+			}
+		}
+
 		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
 			      intel_encoder->base.name);
 
-- 
1.7.9.5

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