linux-kernel - [PATCH 28/45] drm/msm/dp: add an API to initialize MST on sink side

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Message-ID: <20241205-dp_mst-v1-28-f8618d42a99a@quicinc.com>
Date: Thu, 5 Dec 2024 20:31:59 -0800
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov
	<dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Simona
 Vetter" <simona@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        "Chandan
 Uddaraju" <chandanu@...eaurora.org>,
        Guenter Roeck <groeck@...omium.org>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
	<conor+dt@...nel.org>
CC: Vara Reddy <quic_varar@...cinc.com>, Rob Clark <robdclark@...omium.org>,
        Tanmay Shah <tanmay@...eaurora.org>, <linux-arm-msm@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Jessica Zhang
	<quic_jesszhan@...cinc.com>,
        Laurent Pinchart
	<laurent.pinchart@...asonboard.com>,
        Abhinav Kumar
	<quic_abhinavk@...cinc.com>
Subject: [PATCH 28/45] drm/msm/dp: add an API to initialize MST on sink
 side

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>
---
 drivers/gpu/drm/msm/dp/dp_display.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index e69cdfbbe10484e47475ef189849f8ff6628bd7a..033d238e956263c1212fce45aab01316ef341edb 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.c
+++ b/drivers/gpu/drm/msm/dp/dp_display.c
@@ -380,6 +380,35 @@ static int msm_dp_display_send_hpd_notification(struct msm_dp_display_private *d
 	return 0;
 }
 
+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 state is not cleared */
+	if (old_mstm_ctrl) {
+		drm_dbg_dp(dp->drm_dev, "MSTM_CTRL is not cleared, wait %luus\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;
@@ -414,6 +443,9 @@ 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->max_stream > DEFAULT_STREAM_COUNT && msm_dp_panel_read_mst_cap(dp->panel))
+		msm_dp_display_mst_init(dp);
+
 	msm_dp_link_reset_phy_params_vx_px(dp->link);
 	rc = msm_dp_ctrl_on_link(dp->ctrl, dp_display->mst_active);
 	if (rc) {

-- 
2.34.1