linux-kernel - [PATCH v2 17/43] drm/bridge: analogix_dp: Wait for HPD signal before configuring link

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Date:   Fri, 26 Jan 2018 14:16:44 +0100
From:   Thierry Escande <thierry.escande@...labora.com>
To:     Archit Taneja <architt@...eaurora.org>,
        Inki Dae <inki.dae@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sandy Huang <hjc@...k-chips.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Tomasz Figa <tfiga@...omium.org>
Cc:     Haixia Shi <hshi@...omium.org>,
        Ørjan Eide <orjan.eide@....com>,
        Zain Wang <wzz@...k-chips.com>,
        Yakir Yang <ykk@...k-chips.com>, Lin Huang <hl@...k-chips.com>,
        Douglas Anderson <dianders@...omium.org>,
        Mark Yao <mark.yao@...k-chips.com>,
        linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org
Subject: [PATCH v2 17/43] 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>
---
 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