linux-kernel - [PATCH v3 26/38] drm/msm/dp: add an API to initialize MST on sink side

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Message-Id: <20250825-msm-dp-mst-v3-26-01faacfcdedd@oss.qualcomm.com>
Date: Mon, 25 Aug 2025 22:16:12 +0800
From: Yongxing Mou <yongxing.mou@....qualcomm.com>
To: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jessica.zhang@....qualcomm.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Yongxing Mou <yongxing.mou@....qualcomm.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Subject: [PATCH v3 26/38] drm/msm/dp: add an API to initialize MST on sink
 side

From: Abhinav Kumar <quic_abhinavk@...cinc.com>

If the DP controller is capable of supporting multiple streams
then initialize the DP sink in MST mode by programming the DP_MSTM_CTRL
DPCD register to enable MST mode.

Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
Signed-off-by: Yongxing Mou <yongxing.mou@....qualcomm.com>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 55 ++++++++++++++++++++++++++++++-------
 1 file changed, 45 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index cb433103d439ac6b8089bdecf0ee6be35c914db1..84df34306fb557341bea288ea8c13b0c81b11919 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -14,6 +14,7 @@
 #include <linux/string_choices.h>
 #include <drm/display/drm_dp_aux_bus.h>
 #include <drm/display/drm_hdmi_audio_helper.h>
+#include <drm/display/drm_dp_mst_helper.h>
 #include <drm/drm_edid.h>
 
 #include "msm_drv.h"
@@ -297,6 +298,35 @@ static int msm_dp_display_lttpr_init(struct msm_dp_display_private *dp, u8 *dpcd
 	return lttpr_count;
 }
 
+static void msm_dp_display_mst_init(struct msm_dp_display_private *dp)
+{
+	const unsigned long clear_mstm_ctrl_timeout_us = 100000;
+	u8 old_mstm_ctrl;
+	struct msm_dp *msm_dp = &dp->msm_dp_display;
+	int ret;
+
+	/* clear sink mst state */
+	drm_dp_dpcd_readb(dp->aux, DP_MSTM_CTRL, &old_mstm_ctrl);
+	drm_dp_dpcd_writeb(dp->aux, DP_MSTM_CTRL, 0);
+
+	/* add extra delay if MST old state is on*/
+	if (old_mstm_ctrl) {
+		drm_dbg_dp(dp->drm_dev, "wait %luus to set DP_MSTM_CTRL set 0\n",
+			   clear_mstm_ctrl_timeout_us);
+		usleep_range(clear_mstm_ctrl_timeout_us,
+			     clear_mstm_ctrl_timeout_us + 1000);
+	}
+
+	ret = drm_dp_dpcd_writeb(dp->aux, DP_MSTM_CTRL,
+				 DP_MST_EN | DP_UP_REQ_EN | DP_UPSTREAM_IS_SRC);
+	if (ret < 0) {
+		DRM_ERROR("sink mst enablement failed\n");
+		return;
+	}
+
+	msm_dp->mst_active = true;
+}
+
 static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
 {
 	struct drm_connector *connector = dp->msm_dp_display.connector;
@@ -315,18 +345,20 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
 	if (rc)
 		goto end;
 
-	drm_edid = drm_edid_read_ddc(connector, &dp->aux->ddc);
-	drm_edid_connector_update(connector, drm_edid);
+	if (!dp->mst_supported || !drm_dp_read_mst_cap(dp->aux, dp->panel->dpcd)) {
+		drm_edid = drm_edid_read_ddc(connector, &dp->aux->ddc);
+		drm_edid_connector_update(connector, drm_edid);
 
-	if (!drm_edid) {
-		DRM_ERROR("panel edid read failed\n");
-		/* check edid read fail is due to unplug */
-		if (!msm_dp_aux_is_link_connected(dp->aux))
-			return -ETIMEDOUT;
-	}
+		if (!drm_edid) {
+			DRM_ERROR("panel edid read failed\n");
+			/* check edid read fail is due to unplug */
+			if (!msm_dp_aux_is_link_connected(dp->aux))
+				return -ETIMEDOUT;
+		}
 
-	if (rc)
-		goto end;
+		if (rc)
+			goto end;
+	}
 
 	msm_dp_link_process_request(dp->link);
 
@@ -349,6 +381,9 @@ static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
 	 */
 	msm_dp_link_psm_config(dp->link, &dp->panel->link_info, false);
 
+	if (dp->mst_supported && drm_dp_read_mst_cap(dp->aux, dp->panel->dpcd))
+		msm_dp_display_mst_init(dp);
+
 	msm_dp_link_reset_phy_params_vx_px(dp->link);
 
 	if (!dp->msm_dp_display.internal_hpd)

-- 
2.34.1