drm/bridge: analogix_dp: Wait for HPD signal before configuring link

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>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423105003.9004-6-enric.balletbo@collabora.com

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
index bf805f15627250d89fd0e213ca83d9bdba721c53..3269deec739df669462d3d1351a95abbf08dcde5 100644 (file)
--- 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 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;