linux-kernel - [PATCH v3 18/38] drm/msm/dp: Add support to enable MST in mainlink control

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Message-Id: <20250825-msm-dp-mst-v3-18-01faacfcdedd@oss.qualcomm.com>
Date: Mon, 25 Aug 2025 22:16:04 +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 18/38] drm/msm/dp: Add support to enable MST in mainlink
 control

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

Add support to program the MST enable bit in the mainlink control
register when an MST session is active or being disabled.

Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
Signed-off-by: Yongxing Mou <yongxing.mou@....qualcomm.com>
---
 drivers/gpu/drm/msm/dp/dp_ctrl.c | 17 +++++++++++++++++
 drivers/gpu/drm/msm/dp/dp_reg.h  |  1 +
 2 files changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
index 16e5ed58e791971d5dca3077cbb77bfcc186505a..d562377a8d2846099bf0f8757128978a162745c3 100644
--- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
+++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
@@ -254,6 +254,19 @@ void msm_dp_ctrl_mst_send_act(struct msm_dp_ctrl *msm_dp_ctrl)
 	return;
 }
 
+static void msm_dp_ctrl_mst_config(struct msm_dp_ctrl_private *ctrl, bool enable)
+{
+	u32 mainlink_ctrl;
+
+	mainlink_ctrl = msm_dp_read_link(ctrl, REG_DP_MAINLINK_CTRL);
+	if (enable)
+		mainlink_ctrl |= DP_MAINLINK_CTRL_MST_EN;
+	else
+		mainlink_ctrl &= ~DP_MAINLINK_CTRL_MST_EN;
+
+	msm_dp_write_link(ctrl, REG_DP_MAINLINK_CTRL, mainlink_ctrl);
+}
+
 /*
  * NOTE: resetting DP controller will also clear any pending HPD related interrupts
  */
@@ -2656,6 +2669,9 @@ int msm_dp_ctrl_on_stream(struct msm_dp_ctrl *msm_dp_ctrl, struct msm_dp_panel *
 	msm_dp_ctrl_lane_mapping(ctrl);
 	msm_dp_setup_peripheral_flush(ctrl);
 
+	if (ctrl->mst_active)
+		msm_dp_ctrl_mst_config(ctrl, true);
+
 	if (msm_dp_panel->stream_id == DP_STREAM_0)
 		msm_dp_ctrl_config_ctrl_link(ctrl);
 
@@ -2711,6 +2727,7 @@ void msm_dp_ctrl_off_link(struct msm_dp_ctrl *msm_dp_ctrl)
 	phy = ctrl->phy;
 
 	msm_dp_ctrl_mainlink_disable(ctrl);
+	msm_dp_ctrl_mst_config(ctrl, false);
 
 	msm_dp_ctrl_reset(&ctrl->msm_dp_ctrl);
 
diff --git a/drivers/gpu/drm/msm/dp/dp_reg.h b/drivers/gpu/drm/msm/dp/dp_reg.h
index de3d0b8b52c269fd7575edf3f4096a4284ad0b8d..fda847b33f8d0d6ec4d2589586b5a3d6c9b1ccf3 100644
--- a/drivers/gpu/drm/msm/dp/dp_reg.h
+++ b/drivers/gpu/drm/msm/dp/dp_reg.h
@@ -128,6 +128,7 @@
 #define DP_MAINLINK_FLUSH_MODE_UPDATE_SDP	FIELD_PREP(DP_MAINLINK_CTRL_FLUSH_MODE_MASK, 1)
 #define DP_MAINLINK_FLUSH_MODE_SDE_PERIPH_UPDATE	FIELD_PREP(DP_MAINLINK_CTRL_FLUSH_MODE_MASK, 3)
 #define DP_MAINLINK_FB_BOUNDARY_SEL		(0x02000000)
+#define DP_MAINLINK_CTRL_MST_EN			(0x04000100)
 
 #define REG_DP_STATE_CTRL			(0x00000004)
 #define DP_STATE_CTRL_LINK_TRAINING_PATTERN1	(0x00000001)

-- 
2.34.1