[PATCH v6 27/29] drm/msm/dp: enable MST on capable sinks
From: Yongxing Mou
Date: Mon Aug 31 2026 - 04:28:39 EST
From: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
MST topology discovery requires the sink to operate in MST mode.
Enable MST on sinks that advertise MST capability and are connected
to a multi-stream capable DP controller.
Once MST is enabled, downstream sink discovery and EDID retrieval are
handled through the MST topology rather than the primary DP connector.
Activate the MST topology manager on connect and disable it on
disconnect to track the sink topology lifecycle.
Snapshot the negotiated link parameters when MST is enabled so
subsequent MST payload allocation can derive bandwidth information
from a stable link configuration.
Signed-off-by: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
Signed-off-by: Yongxing Mou <yongxing.mou@xxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/msm/dp/dp_display.c | 59 ++++++++++++++++++++++++++++++++-----
drivers/gpu/drm/msm/dp/dp_display.h | 2 ++
drivers/gpu/drm/msm/dp/dp_mst_drm.c | 18 +++++++++++
drivers/gpu/drm/msm/dp/dp_mst_drm.h | 1 +
4 files changed, 73 insertions(+), 7 deletions(-)
diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
index f350c1d03b06..dbc0e82d333a 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"
@@ -269,6 +270,29 @@ static int msm_dp_display_lttpr_init(struct msm_dp_display_private *dp, u8 *dpcd
return lttpr_count;
}
+static void msm_dp_display_mst_enable(struct msm_dp_display_private *dp)
+{
+ struct msm_dp *msm_dp = &dp->msm_dp_display;
+ int ret;
+
+ /* Clear any pre-existing MST state before enabling MST. */
+ ret = drm_dp_dpcd_write_byte(dp->aux, DP_MSTM_CTRL, 0);
+ if (ret < 0) {
+ DRM_ERROR("failed to clear DP_MSTM_CTRL, ret=%d\n", ret);
+ return;
+ }
+
+ ret = drm_dp_dpcd_write_byte(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;
+ msm_dp_mst_display_set_mgr_state(msm_dp, true);
+}
+
static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
{
struct drm_connector *connector = dp->msm_dp_display.connector;
@@ -287,14 +311,17 @@ 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 (msm_dp_ctrl_get_stream_cnt(dp->ctrl) <= 1 ||
+ !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;
+ }
}
msm_dp_link_process_request(dp->link);
@@ -316,6 +343,10 @@ 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 (msm_dp_ctrl_get_stream_cnt(dp->ctrl) > 1 &&
+ drm_dp_read_mst_cap(dp->aux, dp->panel->dpcd))
+ msm_dp_display_mst_enable(dp);
+
msm_dp_link_reset_phy_params_vx_px(dp->link);
end:
@@ -490,6 +521,11 @@ static int msm_dp_hpd_unplug_handle(struct msm_dp_display_private *dp)
dp->panel->dpcd,
dp->panel->downstream_ports);
+ if (dp->msm_dp_display.mst_active) {
+ msm_dp_mst_display_set_mgr_state(&dp->msm_dp_display, false);
+ dp->msm_dp_display.mst_active = false;
+ }
+
/* signal the disconnect event early to ensure proper teardown */
msm_dp_display_handle_plugged_change(&dp->msm_dp_display, false);
@@ -566,6 +602,15 @@ struct msm_dp_panel *msm_dp_display_get_panel(struct msm_dp *msm_dp_display,
return dp_panel;
}
+void msm_dp_display_get_link_info(struct msm_dp *msm_dp_display,
+ struct msm_dp_link_info *link_info)
+{
+ struct msm_dp_display_private *dp =
+ container_of(msm_dp_display, struct msm_dp_display_private, msm_dp_display);
+
+ memcpy(link_info, &dp->panel->link_info, sizeof(*link_info));
+}
+
static void msm_dp_display_deinit_sub_modules(struct msm_dp_display_private *dp)
{
msm_dp_audio_put(dp->audio);
diff --git a/drivers/gpu/drm/msm/dp/dp_display.h b/drivers/gpu/drm/msm/dp/dp_display.h
index ca2faf478c95..96b53d5b6090 100644
--- a/drivers/gpu/drm/msm/dp/dp_display.h
+++ b/drivers/gpu/drm/msm/dp/dp_display.h
@@ -65,4 +65,6 @@ int msm_dp_get_mst_max_stream(struct msm_dp *msm_dp_display);
int msm_dp_mst_register(struct msm_dp *msm_dp_display);
struct msm_dp_panel *msm_dp_display_get_panel(struct msm_dp *msm_dp_display,
enum msm_dp_stream_id stream_id);
+void msm_dp_display_get_link_info(struct msm_dp *msm_dp_display,
+ struct msm_dp_link_info *link_info);
#endif /* _DP_DISPLAY_H_ */
diff --git a/drivers/gpu/drm/msm/dp/dp_mst_drm.c b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
index 2e625a7db981..b2905c894ce5 100644
--- a/drivers/gpu/drm/msm/dp/dp_mst_drm.c
+++ b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
@@ -328,6 +328,24 @@ int msm_dp_mst_attach_encoder(struct msm_dp *dp_display, unsigned int stream_id,
return 0;
}
+int msm_dp_mst_display_set_mgr_state(struct msm_dp *dp_display, bool state)
+{
+ struct msm_dp_mst *mst = dp_display->msm_dp_mst;
+ int rc;
+
+ rc = drm_dp_mst_topology_mgr_set_mst(&mst->mst_mgr, state);
+ if (rc < 0) {
+ drm_err(dp_display->drm_dev,
+ "[MST] failed to set topology mgr state to %d rc:%d\n", state, rc);
+ }
+
+ if (state)
+ msm_dp_display_get_link_info(dp_display, &mst->link_info);
+
+ drm_dbg_kms(dp_display->drm_dev, "[MST] set_mgr_state state:%d\n", state);
+ return rc;
+}
+
void msm_dp_mst_display_hpd_irq(struct msm_dp *dp_display)
{
int rc;
diff --git a/drivers/gpu/drm/msm/dp/dp_mst_drm.h b/drivers/gpu/drm/msm/dp/dp_mst_drm.h
index 8546214cbca1..4a5707dd50a9 100644
--- a/drivers/gpu/drm/msm/dp/dp_mst_drm.h
+++ b/drivers/gpu/drm/msm/dp/dp_mst_drm.h
@@ -10,6 +10,7 @@
int msm_dp_mst_mgr_init(struct msm_dp *dp_display, u32 max_streams, struct drm_dp_aux *drm_aux);
int msm_dp_mst_attach_encoder(struct msm_dp *dp_display, unsigned int stream_id,
struct drm_encoder *encoder);
+int msm_dp_mst_display_set_mgr_state(struct msm_dp *dp_display, bool state);
void msm_dp_mst_display_hpd_irq(struct msm_dp *dp_display);
#endif /* _DP_MST_DRM_H_ */
--
2.43.0