[PATCH v15 07/11] drm/mediatek: Add retry to prevent misjudgment for sink devices

[Bo-Chen Chen]

For some DP dungles, we need to train more than onece to confirm that we
don't misjudge the status of sink device.

Signed-off-by: Bo-Chen Chen <rex-bc.chen at mediatek.com>
---
 drivers/gpu/drm/mediatek/mtk_dp.c | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index ce817cb59445..80d7d6488105 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -42,6 +42,7 @@
 #define MTK_DP_CHECK_SINK_CAP_TIMEOUT_COUNT 3
 #define MTK_DP_TBC_BUF_READ_START_ADDR 0x08
 #define MTK_DP_TRAIN_DOWNSCALE_RETRY 8
+#define MTK_DP_TRAIN_CLEAR_RETRY 50
 
 struct mtk_dp_train_info {
 	bool tps3;
@@ -1431,11 +1432,25 @@ static int mtk_dp_video_config(struct mtk_dp *mtk_dp)
 
 static int mtk_dp_training(struct mtk_dp *mtk_dp)
 {
+	short max_retry = MTK_DP_TRAIN_CLEAR_RETRY;
 	int ret;
 
-	ret = mtk_dp_train_start(mtk_dp);
-	if (ret)
-		return ret;
+	/*
+	 * We do retry to confirm that we don't misjudge the sink status.
+	 * If it is still failed, we can confirm there are some issues for the
+	 * sink device.
+	 */
+	do {
+		ret = mtk_dp_train_start(mtk_dp);
+		if (!ret)
+			break;
+	} while (--max_retry);
+
+	dev_info(mtk_dp->dev, "dp training clear retry times: %d\n",
+		 MTK_DP_TRAIN_CLEAR_RETRY - max_retry);
+
+	if (!max_retry)
+		return -ETIMEDOUT;
 
 	ret = mtk_dp_video_config(mtk_dp);
 	if (ret)
-- 
2.18.0