linux-kernel - [PATCH] drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training

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Message-ID: <1662571300-4898-1-git-send-email-quic_khsieh@quicinc.com>
Date:   Wed, 7 Sep 2022 10:21:40 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     <robdclark@...il.com>, <sean@...rly.run>, <swboyd@...omium.org>,
        <dianders@...omium.org>, <vkoul@...nel.org>, <daniel@...ll.ch>,
        <airlied@...ux.ie>, <agross@...nel.org>,
        <dmitry.baryshkov@...aro.org>, <bjorn.andersson@...aro.org>
CC:     <quic_abhinavk@...cinc.com>, <quic_khsieh@...cinc.com>,
        <quic_sbillaka@...cinc.com>, <freedreno@...ts.freedesktop.org>,
        <dri-devel@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm/msm/dp: cleared DP_DOWNSPREAD_CTRL register before start link training

DOWNSPREAD_CTRL (0x107) shall be cleared to 0 upon power-on reset or an
upstream device disconnect. This patch will enforce this rule by always
cleared DOWNPREAD_CTRL register to 0 before start link training. At rare
case that DP MSA timing parameters may be mis-interpreted by the sinker
which causes audio sampling rate be calculated wrongly and cause audio
did not work at sinker if DOWNSPREAD_CTRL register is not cleared to 0.
This patch also make sure bring sinker out of D3 power-down mode into D0
(normal operation mode) successfully by retrying 3 times.

Fixes: 154b5a7da0fd ("drm/msm/dp: add displayPort driver support")
Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
---
 drivers/gpu/drm/msm/dp/dp_ctrl.c |  5 ++---
 drivers/gpu/drm/msm/dp/dp_link.c | 17 +++++++++++------
 2 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index ab6aa13..e864a6e 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -1245,7 +1245,7 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
 {
 	int ret = 0;
 	const u8 *dpcd = ctrl->panel->dpcd;
-	u8 encoding = DP_SET_ANSI_8B10B;
+	u8 encoding[2] = {0, DP_SET_ANSI_8B10B};
 	u8 ssc;
 	u8 assr;
 	struct dp_link_info link_info = {0};
@@ -1263,8 +1263,7 @@ static int dp_ctrl_link_train(struct dp_ctrl_private *ctrl,
 		drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, &ssc, 1);
 	}
 
-	drm_dp_dpcd_write(ctrl->aux, DP_MAIN_LINK_CHANNEL_CODING_SET,
-				&encoding, 1);
+	drm_dp_dpcd_write(ctrl->aux, DP_DOWNSPREAD_CTRL, encoding, 2);
 
 	if (drm_dp_alternate_scrambler_reset_cap(dpcd)) {
 		assr = DP_ALTERNATE_SCRAMBLER_RESET_ENABLE;
diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
index 36f0af0..3ad3826 100644
--- a/drivers/gpu/drm/msm/dp/dp_link.c
+++ b/drivers/gpu/drm/msm/dp/dp_link.c
@@ -49,7 +49,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 					struct dp_link_info *link)
 {
 	u8 value;
-	int err;
+	int i, err;
 
 	if (link->revision < 0x11)
 		return 0;
@@ -61,11 +61,16 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
 	value &= ~DP_SET_POWER_MASK;
 	value |= DP_SET_POWER_D0;
 
-	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
-	if (err < 0)
-		return err;
-
-	usleep_range(1000, 2000);
+	/*
+	 * When turning on, we need to retry for 1ms to give the sink
+	 * time to wake up.
+	 */
+	for (i = 0; i < 3; i++) {
+	        err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+		usleep_range(1000, 2000);
+		if (err == 1)
+			break;
+	}
 
 	return 0;
 }
-- 
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