[PATCH 19/41] drm/bridge: analogix_dp: Wait for HPD signal before configuring link

[Sean Paul]

From: zain wang <wzz at rock-chips.com>

According to DP spec v1.3 chap 3.5.1.2 Link Training, Link Policy Maker
must first detect that the HPD signal is asserted high by the Downstream
Device before establishing a link with it.

Cc: Stéphane Marchesin <marcheu at chromium.org>
Signed-off-by: zain wang <wzz at rock-chips.com>
Signed-off-by: Sean Paul <seanpaul at chromium.org>
---
 drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index f3eea7636a2e..048b6f7c9b6e 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1172,6 +1172,15 @@ static int analogix_dp_set_bridge(struct analogix_dp_device *dp)
 	if (ret)
 		goto out_dp_init;
 
+	/* According to DP spec v1.3 chap 3.5.1.2 Link Training,
+	 * We should first make sure the HPD signal is asserted high by device
+	 * when we want to establish a link with it. */
+	ret = analogix_dp_detect_hpd(dp);
+	if (ret) {
+		DRM_ERROR("failed to get hpd single ret = %d\n", ret);
+		goto out_dp_init;
+	}
+
 	ret = analogix_dp_commit(dp);
 	if (ret)
 		goto out_dp_init;
-- 
2.12.0.246.ga2ecc84866-goog