linux-kernel - [PATCH v3 6/6] drm/msm/dp: do not end dp link training until video is ready

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Message-Id: <1628196295-7382-7-git-send-email-khsieh@codeaurora.org>
Date:   Thu,  5 Aug 2021 13:44:55 -0700
From:   Kuogee Hsieh <khsieh@...eaurora.org>
To:     dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org
Cc:     Kuogee Hsieh <khsieh@...eaurora.org>, abhinavk@...eaurora.org,
        aravindh@...eaurora.org, airlied@...ux.ie, daniel@...ll.ch,
        bjorn.andersson@...aro.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 6/6] drm/msm/dp: do not end dp link training until video is ready

Initialize both pre-emphasis and voltage swing level to 0 before
start link training and do not end link training until video is
ready to reduce the period between end of link training and video
start to meet Link Layer CTS requirement.  Some dongle main link
symbol may become unlocked again if host did not end link training
soon enough after completion of link training 2. Host have to re
train main link if loss of symbol locked detected before end link
training so that the coming video stream can be transmitted to sink
properly. This fixes Link Layer CTS cases 4.3.2.1, 4.3.2.2, 4.3.2.3
and 4.3.2.4.

Changes in v3:
-- merge retrain link if loss of symbol locked happen into this patch
-- replace dp_ctrl_loss_symbol_lock() with dp_ctrl_channel_eq_ok()

Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
---
 drivers/gpu/drm/msm/dp/dp_ctrl.c | 56 +++++++++++++++++++++++++++++-----------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index 0002805..ffed523 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -1484,6 +1484,9 @@ static int dp_ctrl_link_maintenance(struct dp_ctrl_private *ctrl)
 
 	dp_ctrl_push_idle(&ctrl->dp_ctrl);
 
+	ctrl->link->phy_params.p_level = 0;
+	ctrl->link->phy_params.v_level = 0;
+
 	ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
 
 	ret = dp_ctrl_setup_main_link(ctrl, &training_step);
@@ -1636,6 +1639,16 @@ static bool dp_ctrl_clock_recovery_any_ok(
 	return drm_dp_clock_recovery_ok(link_status, reduced_cnt);
 }
 
+static bool dp_ctrl_channel_eq_ok(struct dp_ctrl_private *ctrl)
+{
+	u8 link_status[DP_LINK_STATUS_SIZE];
+	int num_lanes = ctrl->link->link_params.num_lanes;
+
+	dp_ctrl_read_link_status(ctrl, link_status);
+
+	return drm_dp_channel_eq_ok(link_status, num_lanes);
+}
+
 int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 {
 	int rc = 0;
@@ -1671,6 +1684,9 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 		ctrl->link->link_params.rate,
 		ctrl->link->link_params.num_lanes, ctrl->dp_ctrl.pixel_rate);
 
+	ctrl->link->phy_params.p_level = 0;
+	ctrl->link->phy_params.v_level = 0;
+
 	rc = dp_ctrl_enable_mainlink_clocks(ctrl);
 	if (rc)
 		return rc;
@@ -1736,17 +1752,19 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 	if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN)
 		return rc;
 
-	/* stop txing train pattern */
-	dp_ctrl_clear_training_pattern(ctrl);
+	if (rc == 0) {  /* link train successfully */
+		/*
+		 * do not stop train pattern here
+		 * stop link training at on_stream
+		 * to pass compliance test
+		 */
+	} else  {
+		/*
+		 * link training failed
+		 * end txing train pattern here
+		 */
+		dp_ctrl_clear_training_pattern(ctrl);
 
-	/*
-	 * keep transmitting idle pattern until video ready
-	 * to avoid main link from loss of sync
-	 */
-	if (rc == 0)  /* link train successfully */
-		dp_ctrl_push_idle(dp_ctrl);
-	else  {
-		/* link training failed */
 		dp_ctrl_deinitialize_mainlink(ctrl);
 		rc = -ECONNRESET;
 	}
@@ -1754,9 +1772,15 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
 	return rc;
 }
 
+static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
+{
+	int training_step = DP_TRAINING_NONE;
+
+	return dp_ctrl_setup_main_link(ctrl, &training_step);
+}
+
 int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
 {
-	u32 rate = 0;
 	int ret = 0;
 	bool mainlink_ready = false;
 	struct dp_ctrl_private *ctrl;
@@ -1766,10 +1790,6 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
 
 	ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
 
-	rate = ctrl->panel->link_info.rate;
-
-	ctrl->link->link_params.rate = rate;
-	ctrl->link->link_params.num_lanes = ctrl->panel->link_info.num_lanes;
 	ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
 
 	DRM_DEBUG_DP("rate=%d, num_lanes=%d, pixel_rate=%d\n",
@@ -1784,6 +1804,12 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
 		}
 	}
 
+	if (!dp_ctrl_channel_eq_ok(ctrl))
+		dp_ctrl_link_retrain(ctrl);
+
+	/* stop txing train pattern to end link training */
+	dp_ctrl_clear_training_pattern(ctrl);
+
 	ret = dp_ctrl_enable_stream_clocks(ctrl);
 	if (ret) {
 		DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
-- 
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