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Subject[PATCH 17/40] drm/bridge: analogix_dp: Wait for HPD signal before configuring link
Date
From: zain wang <wzz@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@chromium.org>
Signed-off-by: zain wang <wzz@rock-chips.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
---
drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index ba2506e17f6d..c940a5bb80ac 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1170,6 +1170,17 @@ 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;
--
2.14.1
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