linux-kernel - [PATCH v3 3/8] drm/msm/dp: Read DPCD and sink count in bridge detect()

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Message-Id: <20260115-hpd-refactor-v3-3-08e2f3bcd2e0@oss.qualcomm.com>
Date: Thu, 15 Jan 2026 09:29:08 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Jessica Zhang <jessica.zhang@....qualcomm.com>
Subject: [PATCH v3 3/8] drm/msm/dp: Read DPCD and sink count in bridge
 detect()

From: Jessica Zhang <jessica.zhang@....qualcomm.com>

Instead of relying on the link_ready flag to specify if DP is connected,
read the DPCD bits and get the sink count to accurately detect if DP is
connected.

Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 60 +++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/msm/dp/dp_drm.c     | 20 -------------
 drivers/gpu/drm/msm/dp/dp_drm.h     |  2 ++
 3 files changed, 62 insertions(+), 20 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index 5997cd28ba11..a05144de3b93 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -1151,6 +1151,66 @@ static int msm_dp_hpd_event_thread_start(struct msm_dp_display_private *msm_dp_p
 	return 0;
 }
 
+/**
+ * msm_dp_bridge_detect - callback to determine if connector is connected
+ * @bridge: Pointer to drm bridge structure
+ * @connector: Pointer to drm connector structure
+ * Returns: Bridge's 'is connected' status
+ */
+enum drm_connector_status msm_dp_bridge_detect(struct drm_bridge *bridge,
+					       struct drm_connector *connector)
+{
+	struct msm_dp_bridge *msm_dp_bridge = to_dp_bridge(bridge);
+	struct msm_dp *dp = msm_dp_bridge->msm_dp_display;
+	struct msm_dp_display_private *priv;
+	int ret = 0;
+	int status = connector_status_disconnected;
+	u8 dpcd[DP_RECEIVER_CAP_SIZE];
+	struct drm_dp_desc desc;
+
+	dp = to_dp_bridge(bridge)->msm_dp_display;
+
+	priv = container_of(dp, struct msm_dp_display_private, msm_dp_display);
+
+	if (!dp->link_ready)
+		return status;
+
+	msm_dp_aux_enable_xfers(priv->aux, true);
+
+	ret = pm_runtime_resume_and_get(&dp->pdev->dev);
+	if (ret) {
+		DRM_ERROR("failed to pm_runtime_resume\n");
+		msm_dp_aux_enable_xfers(priv->aux, false);
+		return status;
+	}
+
+	ret = msm_dp_aux_is_link_connected(priv->aux);
+	if (dp->internal_hpd && !ret)
+		goto end;
+
+	ret = drm_dp_read_dpcd_caps(priv->aux, dpcd);
+	if (ret)
+		goto end;
+
+	ret = drm_dp_read_desc(priv->aux, &desc, drm_dp_is_branch(dpcd));
+	if (ret)
+		goto end;
+
+	status = connector_status_connected;
+	if (drm_dp_read_sink_count_cap(connector, dpcd, &desc)) {
+		int sink_count = drm_dp_read_sink_count(priv->aux);
+
+		drm_dbg_dp(dp->drm_dev, "sink_count = %d\n", sink_count);
+
+		if (sink_count <= 0)
+			status = connector_status_disconnected;
+	}
+
+end:
+	pm_runtime_put_sync(&dp->pdev->dev);
+	return status;
+}
+
 static irqreturn_t msm_dp_display_irq_handler(int irq, void *dev_id)
 {
 	struct msm_dp_display_private *dp = dev_id;
diff --git a/drivers/gpu/drm/msm/dp/dp_drm.c b/drivers/gpu/drm/msm/dp/dp_drm.c
index fd6443d2b6ce..e4622c85fb66 100644
--- a/drivers/gpu/drm/msm/dp/dp_drm.c
+++ b/drivers/gpu/drm/msm/dp/dp_drm.c
@@ -15,26 +15,6 @@
 #include "dp_audio.h"
 #include "dp_drm.h"
 
-/**
- * msm_dp_bridge_detect - callback to determine if connector is connected
- * @bridge: Pointer to drm bridge structure
- * @connector: Pointer to drm connector structure
- * Returns: Bridge's 'is connected' status
- */
-static enum drm_connector_status
-msm_dp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
-{
-	struct msm_dp *dp;
-
-	dp = to_dp_bridge(bridge)->msm_dp_display;
-
-	drm_dbg_dp(dp->drm_dev, "link_ready = %s\n",
-		str_true_false(dp->link_ready));
-
-	return (dp->link_ready) ? connector_status_connected :
-					connector_status_disconnected;
-}
-
 static int msm_dp_bridge_atomic_check(struct drm_bridge *bridge,
 			    struct drm_bridge_state *bridge_state,
 			    struct drm_crtc_state *crtc_state,
diff --git a/drivers/gpu/drm/msm/dp/dp_drm.h b/drivers/gpu/drm/msm/dp/dp_drm.h
index 9eb3431dd93a..6c0426803d78 100644
--- a/drivers/gpu/drm/msm/dp/dp_drm.h
+++ b/drivers/gpu/drm/msm/dp/dp_drm.h
@@ -25,6 +25,8 @@ int msm_dp_bridge_init(struct msm_dp *msm_dp_display, struct drm_device *dev,
 		   struct drm_encoder *encoder,
 		   bool yuv_supported);
 
+enum drm_connector_status msm_dp_bridge_detect(struct drm_bridge *bridge,
+					       struct drm_connector *connector);
 void msm_dp_bridge_atomic_enable(struct drm_bridge *drm_bridge,
 				 struct drm_atomic_state *state);
 void msm_dp_bridge_atomic_disable(struct drm_bridge *drm_bridge,

-- 
2.47.3