linux-kernel - [PATCH v4 drm-dp 05/11] drm/hisilicon/hibmc: fix rare monitors cannot display problem

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Message-ID: <20250813094238.3722345-6-shiyongbang@huawei.com>
Date: Wed, 13 Aug 2025 17:42:32 +0800
From: Yongbang Shi <shiyongbang@...wei.com>
To: <xinliang.liu@...aro.org>, <tiantao6@...ilicon.com>,
	<maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
	<tzimmermann@...e.de>, <airlied@...il.com>, <daniel@...ll.ch>,
	<kong.kongxinwei@...ilicon.com>, <dmitry.baryshkov@....qualcomm.com>
CC: <liangjian010@...wei.com>, <chenjianmin@...wei.com>,
	<fengsheng5@...wei.com>, <shiyongbang@...wei.com>, <libaihan@...wei.com>,
	<shenjian15@...wei.com>, <shaojijie@...wei.com>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v4 drm-dp 05/11] drm/hisilicon/hibmc: fix rare monitors cannot display problem

From: Baihan Li <libaihan@...wei.com>

In some case, the dp link training success at 8.1Gbps, but the sink's
maximum supported rate is less than 8.1G. So change the default 8.1Gbps
link rate to the rate that reads from devices' capabilities.

Fixes: 54063d86e036 ("drm/hisilicon/hibmc: add dp link moduel in hibmc drivers")
Signed-off-by: Baihan Li <libaihan@...wei.com>
Signed-off-by: Yongbang Shi <shiyongbang@...wei.com>
---
ChangeLog:
v3 -> v4:
  - remove non-related changes, suggested by Dmitry Baryshkov.
---
 drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c b/drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c
index 74f7832ea53e..0726cb5b736e 100644
--- a/drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c
+++ b/drivers/gpu/drm/hisilicon/hibmc/dp/dp_link.c
@@ -325,6 +325,17 @@ static int hibmc_dp_link_downgrade_training_eq(struct hibmc_dp_dev *dp)
 	return hibmc_dp_link_reduce_rate(dp);
 }
 
+static void hibmc_dp_update_caps(struct hibmc_dp_dev *dp)
+{
+	dp->link.cap.link_rate = dp->dpcd[DP_MAX_LINK_RATE];
+	if (dp->link.cap.link_rate > DP_LINK_BW_8_1 || !dp->link.cap.link_rate)
+		dp->link.cap.link_rate = DP_LINK_BW_8_1;
+
+	dp->link.cap.lanes = dp->dpcd[DP_MAX_LANE_COUNT] & DP_MAX_LANE_COUNT_MASK;
+	if (dp->link.cap.lanes > HIBMC_DP_LANE_NUM_MAX)
+		dp->link.cap.lanes = HIBMC_DP_LANE_NUM_MAX;
+}
+
 int hibmc_dp_link_training(struct hibmc_dp_dev *dp)
 {
 	struct hibmc_dp_link *link = &dp->link;
@@ -334,8 +345,7 @@ int hibmc_dp_link_training(struct hibmc_dp_dev *dp)
 	if (ret)
 		drm_err(dp->dev, "dp aux read dpcd failed, ret: %d\n", ret);
 
-	dp->link.cap.link_rate = dp->dpcd[DP_MAX_LINK_RATE];
-	dp->link.cap.lanes = 0x2;
+	hibmc_dp_update_caps(dp);
 
 	ret = hibmc_dp_get_serdes_rate_cfg(dp);
 	if (ret < 0)
-- 
2.33.0