On Saturday 10 March 2018 03:53 AM, Enric Balletbo i Serra wrote:
From: zain wang <w...@rock-chips.com>

According to DP spec v1.3 chap 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.

Reviewed-by: Archit Taneja <arch...@codeaurora.org>


Cc: Stéphane Marchesin <marc...@chromium.org>
Signed-off-by: zain wang <w...@rock-chips.com>
Signed-off-by: Sean Paul <seanp...@chromium.org>
Signed-off-by: Thierry Escande <thierry.esca...@collabora.com>
Signed-off-by: Enric Balletbo i Serra <enric.balle...@collabora.com>
Tested-by: Marek Szyprowski <m.szyprow...@samsung.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 
index c81733b8185e..92fb9a072cb6 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
@@ -1169,6 +1169,17 @@ static int analogix_dp_set_bridge(struct 
analogix_dp_device *dp)
        if (ret)
                goto out_dp_init;
+ /*
+        * According to DP spec v1.3 chap 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;

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