linux-kernel - [PATCH RESEND] drm/bridge: Fixed a DP link training bug

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Date: Thu, 21 Dec 2023 17:30:57 +0800
From: xiazhengqiao <xiazhengqiao@...qin.corp-partner.google.com>
To: dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Cc: neil.armstrong@...aro.org,
	rfoss@...nel.org,
	jonas@...boo.se,
	sam@...nborg.org,
	jernej.skrabec@...il.com,
	allen.chen@....corp-partner.google.com,
	Laurent.pinchart@...asonboard.com,
	andrzej.hajda@...el.com,
	dianders@...gle.com,
	hsinyi@...gle.com,
	xiazhengqiao <xiazhengqiao@...qin.corp-partner.google.com>
Subject: [PATCH RESEND] drm/bridge: Fixed a DP link training bug

To have better compatibility for DP sink, there is a retry mechanism
for the link training process to switch between different training process.
The original driver code doesn't reset the retry counter when training
state is pass. If the system triggers link training over 3 times,
there will be a chance to causes the driver to use the wrong training
method and return a training fail result.

To Fix this, we reset the retry counter when training state is pass
each time.

Signed-off-by: Allen Chen <allen.chen@....corp-partner.google.com>
Signed-off-by: xiazhengqiao <xiazhengqiao@...qin.corp-partner.google.com>
---
 drivers/gpu/drm/bridge/ite-it6505.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
index 2f300f5ca051..b589136ca6da 100644
--- a/drivers/gpu/drm/bridge/ite-it6505.c
+++ b/drivers/gpu/drm/bridge/ite-it6505.c
@@ -2240,11 +2240,13 @@ static void it6505_link_training_work(struct work_struct *work)
 	ret = it6505_link_start_auto_train(it6505);
 	DRM_DEV_DEBUG_DRIVER(dev, "auto train %s, auto_train_retry: %d",
 			     ret ? "pass" : "failed", it6505->auto_train_retry);
-	it6505->auto_train_retry--;
 
 	if (ret) {
+		it6505->auto_train_retry = AUTO_TRAIN_RETRY;
 		it6505_link_train_ok(it6505);
 		return;
+	} else {
+		it6505->auto_train_retry--;
 	}
 
 	it6505_dump(it6505);
-- 
2.17.1