linux-kernel - [PATCH v4 13/38] drm/bridge: analogix_dp: Wait for HPD signal before configuring link

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Date:   Mon,  5 Mar 2018 23:23:05 +0100
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     architt@...eaurora.org, inki.dae@...sung.com,
        thierry.reding@...il.com, hjc@...k-chips.com,
        seanpaul@...omium.org, airlied@...ux.ie, tfiga@...omium.org,
        heiko@...ech.de
Cc:     hshi@...omium.org, wzz@...k-chips.com, hl@...k-chips.com,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        dianders@...omium.org, linux-rockchip@...ts.infradead.org,
        orjan.eide@....com, m.szyprowski@...sung.com,
        Stéphane Marchesin <marcheu@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>
Subject: [PATCH v4 13/38] drm/bridge: analogix_dp: Wait for HPD signal before configuring link

From: zain wang <wzz@...k-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@...omium.org>
Signed-off-by: zain wang <wzz@...k-chips.com>
Signed-off-by: Sean Paul <seanpaul@...omium.org>
Signed-off-by: Thierry Escande <thierry.escande@...labora.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.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 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 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;
-- 
2.16.1