Re: [PATCH v4 36/39] drm/msm/dp: add connector abstraction for DP MST

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

On Fri, Apr 10, 2026 at 05:34:11PM +0800, Yongxing Mou wrote:
> From: Abhinav Kumar <quic_abhinavk@quicinc.com>
> 
> Introduce an MST connector abstraction for DP MST, with each MST
> connector associated with a DP panel and connected through a DRM bridge
> to an MST encoder.
> 
> The connector is only used for MST helper callbacks, such as detect,
> get_modes, and get_encoder. Display enable/disable, hotplug handling,
> and modeset sequencing continue to be handled by the bridge path.
> 
> Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
> Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_mst_drm.c | 231 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 231 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_mst_drm.c b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> index 4df3ea5e36d0..bb3898b1f6b1 100644
> --- a/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> +++ b/drivers/gpu/drm/msm/dp/dp_mst_drm.c
> @@ -7,6 +7,7 @@
>  #include <drm/drm_managed.h>
>  #include <drm/drm_bridge.h>
>  #include <drm/display/drm_dp_mst_helper.h>
> +#include <linux/pm_runtime.h>
>  
>  #include "dp_mst_drm.h"
>  #include "dp_panel.h"
> @@ -489,6 +490,235 @@ int msm_dp_mst_display_set_mgr_state(struct msm_dp *dp_display, bool state)
>  	return rc;
>  }
>  
> +/* DP MST Connector OPs */
> +static int
> +msm_dp_mst_connector_detect(struct drm_connector *connector,
> +			    struct drm_modeset_acquire_ctx *ctx,
> +			    bool force)
> +{
> +	struct msm_dp_mst_connector *mst_conn = to_dp_mst_connector(connector);
> +	struct msm_dp_mst *mst = mst_conn->dp_mst;
> +	struct msm_dp *dp_display = mst->msm_dp;
> +	struct device *dev = dp_display->drm_dev->dev;
> +	enum drm_connector_status status = connector_status_disconnected;
> +	int ret;
> +
> +	ret = pm_runtime_resume_and_get(dev);
> +	if (ret < 0)
> +		return status;
> +
> +	if (dp_display->mst_active)
> +		status = drm_dp_mst_detect_port(connector,
> +						ctx, &mst->mst_mgr, mst_conn->mst_port);
> +
> +	pm_runtime_put_autosuspend(dev);
> +
> +	return status;
> +}
> +
> +static int msm_dp_mst_connector_get_modes(struct drm_connector *connector)
> +{
> +	struct msm_dp_mst_connector *mst_conn = to_dp_mst_connector(connector);
> +	struct msm_dp_mst *mst = mst_conn->dp_mst;
> +	const struct drm_edid *drm_edid;
> +
> +	drm_edid = drm_dp_mst_edid_read(connector, &mst->mst_mgr, mst_conn->mst_port);
> +	drm_edid_connector_update(connector, drm_edid);

Missing drm_edid_free()

> +
> +	return drm_edid_connector_add_modes(connector);
> +}
> +
> +static enum drm_mode_status msm_dp_mst_connector_mode_valid(struct drm_connector *connector,
> +							    const struct drm_display_mode *mode)
> +{
> +	struct msm_dp_mst_connector *mst_conn;
> +	struct drm_dp_mst_port *mst_port;
> +	struct msm_dp *dp_display;
> +	int required_pbn;
> +
> +	if (drm_connector_is_unregistered(connector))
> +		return 0;
> +
> +	mst_conn = to_dp_mst_connector(connector);
> +	mst_port = mst_conn->mst_port;
> +	dp_display = mst_conn->dp_mst->msm_dp;
> +
> +	if (!mst_port)
> +		return MODE_ERROR;

Protective coding?

> +
> +	required_pbn = drm_dp_calc_pbn_mode(mode->clock, (6 * 3) << 4);

Can we actually support 18bpp? At least it deserves a FIXME for bpp
negotiation (for the DSC, etc.). More practically, we have YUV,
espcially YUV 4:2:0, which uses less than 18bpp, if I'm not mistaken.

> +
> +	if (required_pbn > mst_port->full_pbn) {
> +		drm_dbg_dp(dp_display->drm_dev, "mode:%s not supported.\n", mode->name);
> +		return MODE_CLOCK_HIGH;
> +	}
> +
> +	return msm_dp_display_mode_valid(dp_display, &connector->display_info, mode);
> +}
> +
> +static struct drm_encoder *
> +msm_dp_mst_atomic_best_encoder(struct drm_connector *connector, struct drm_atomic_state *state)
> +{
> +	struct msm_dp_mst_connector *mst_conn = to_dp_mst_connector(connector);
> +	struct msm_dp_mst *mst = mst_conn->dp_mst;
> +	struct msm_dp *dp_display = mst->msm_dp;
> +	struct drm_encoder *enc = NULL;
> +	struct msm_dp_mst_bridge_state *mst_bridge_state;
> +	u32 i;
> +	struct drm_connector_state *conn_state = drm_atomic_get_new_connector_state(state,
> +										    connector);
> +
> +	if (conn_state && conn_state->best_encoder)
> +		return conn_state->best_encoder;
> +
> +	for (i = 0; i < mst->max_streams; i++) {
> +		mst_bridge_state = msm_dp_mst_br_priv_state(state, mst->mst_bridge[i]);
> +		if (IS_ERR(mst_bridge_state))
> +			goto end;
> +
> +		if (mst_bridge_state->connector == connector) {
> +			enc = mst->mst_bridge[i]->encoder;
> +			goto end;
> +		}
> +	}

I thought you wanted to get rid of the msm_dp_mst_bridge_state. Let me
see...

> +
> +	for (i = 0; i < mst->max_streams; i++) {
> +		mst_bridge_state = msm_dp_mst_br_priv_state(state, mst->mst_bridge[i]);
> +
> +		if (!mst_bridge_state->connector) {
> +			mst_bridge_state->connector = connector;
> +			mst_bridge_state->msm_dp_panel = mst_conn->dp_panel;
> +			enc = mst->mst_bridge[i]->encoder;
> +			break;
> +		}
> +	}
> +
> +end:
> +	if (enc)
> +		drm_dbg_dp(dp_display->drm_dev, "MST connector:%d atomic best encoder:%d\n",
> +			   connector->base.id, i);
> +	else
> +		drm_dbg_dp(dp_display->drm_dev, "MST connector:%d atomic best encoder failed\n",
> +			   connector->base.id);
> +
> +	return enc;
> +}
> +
> +static int msm_dp_mst_connector_atomic_check(struct drm_connector *connector,
> +					     struct drm_atomic_state *state)
> +{
> +	struct msm_dp_mst_connector *mst_conn = to_dp_mst_connector(connector);
> +	struct msm_dp_mst *mst = mst_conn->dp_mst;
> +
> +	return drm_dp_atomic_release_time_slots(state, &mst->mst_mgr, mst_conn->mst_port);
> +}
> +
> +static void dp_mst_connector_destroy(struct drm_connector *connector)
> +{
> +	struct msm_dp_mst_connector *mst_conn = to_dp_mst_connector(connector);
> +
> +	drm_connector_cleanup(connector);
> +	drm_dp_mst_put_port_malloc(mst_conn->mst_port);
> +	kfree(mst_conn);
> +}
> +
> +/* DRM MST callbacks */
> +static const struct drm_connector_helper_funcs msm_dp_drm_mst_connector_helper_funcs = {
> +	.get_modes =    msm_dp_mst_connector_get_modes,
> +	.detect_ctx =   msm_dp_mst_connector_detect,
> +	.mode_valid =   msm_dp_mst_connector_mode_valid,
> +	.atomic_best_encoder = msm_dp_mst_atomic_best_encoder,
> +	.atomic_check = msm_dp_mst_connector_atomic_check,
> +};
> +
> +static const struct drm_connector_funcs msm_dp_drm_mst_connector_funcs = {
> +	.reset = drm_atomic_helper_connector_reset,
> +	.destroy = dp_mst_connector_destroy,
> +	.fill_modes = drm_helper_probe_single_connector_modes,
> +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static struct drm_connector *
> +msm_dp_mst_add_connector(struct drm_dp_mst_topology_mgr *mgr,
> +			 struct drm_dp_mst_port *port, const char *pathprop)
> +{
> +	struct msm_dp_mst *dp_mst;
> +	struct drm_device *dev;
> +	struct msm_dp *dp_display;
> +	struct msm_dp_mst_connector *mst_conn;
> +	struct drm_connector *connector;
> +	int rc, i;
> +
> +	dp_mst = container_of(mgr, struct msm_dp_mst, mst_mgr);
> +
> +	dp_display = dp_mst->msm_dp;
> +	dev = dp_display->drm_dev;
> +
> +	mst_conn = kzalloc_obj(*mst_conn);
> +
> +	if (!mst_conn)
> +		return NULL;
> +
> +	drm_modeset_lock_all(dev);

What for?

> +
> +	connector = &mst_conn->connector;
> +	rc = drm_connector_dynamic_init(dev, connector,
> +					&msm_dp_drm_mst_connector_funcs,
> +					DRM_MODE_CONNECTOR_DisplayPort, NULL);
> +	if (rc) {
> +		kfree(mst_conn);
> +		drm_modeset_unlock_all(dev);
> +		return NULL;
> +	}
> +
> +	mst_conn->dp_panel = msm_dp_display_get_panel(dp_display);
> +	if (!mst_conn->dp_panel) {
> +		DRM_ERROR("failed to get dp_panel for connector\n");
> +		kfree(mst_conn);
> +		drm_modeset_unlock_all(dev);
> +		return NULL;
> +	}
> +
> +	mst_conn->dp_panel->connector = connector;
> +	mst_conn->dp_mst = dp_mst;
> +
> +	drm_connector_helper_add(connector, &msm_dp_drm_mst_connector_helper_funcs);
> +
> +	if (connector->funcs->reset)
> +		connector->funcs->reset(connector);
> +
> +	/* add all encoders as possible encoders */
> +	for (i = 0; i < dp_mst->max_streams; i++) {
> +		rc = drm_connector_attach_encoder(connector, dp_mst->mst_bridge[i]->encoder);
> +
> +		if (rc) {
> +			DRM_ERROR("failed to attach encoder to connector, %d\n", rc);
> +			kfree(mst_conn);
> +			drm_modeset_unlock_all(dev);
> +			return NULL;
> +		}
> +	}
> +
> +	mst_conn->mst_port = port;
> +	drm_dp_mst_get_port_malloc(mst_conn->mst_port);
> +
> +	drm_object_attach_property(&connector->base,
> +				   dev->mode_config.path_property, 0);
> +	drm_object_attach_property(&connector->base,
> +				   dev->mode_config.tile_property, 0);
> +	drm_connector_set_path_property(connector, pathprop);
> +	drm_modeset_unlock_all(dev);
> +
> +	drm_dbg_dp(dp_display->drm_dev, "add MST connector id:%d\n", connector->base.id);
> +
> +	return connector;
> +}
> +
> +static const struct drm_dp_mst_topology_cbs msm_dp_mst_drm_cbs = {
> +	.add_connector = msm_dp_mst_add_connector,
> +};
> +
>  int msm_dp_mst_init(struct msm_dp *dp_display, u32 max_streams, struct drm_dp_aux *drm_aux)
>  {
>  	struct drm_device *dev = dp_display->drm_dev;
> @@ -501,6 +731,7 @@ int msm_dp_mst_init(struct msm_dp *dp_display, u32 max_streams, struct drm_dp_au
>  		return -ENOMEM;
>  
>  	memset(&msm_dp_mst->mst_mgr, 0, sizeof(msm_dp_mst->mst_mgr));
> +	msm_dp_mst->mst_mgr.cbs = &msm_dp_mst_drm_cbs;
>  	conn_base_id = dp_display->connector->base.id;
>  	msm_dp_mst->msm_dp = dp_display;
>  	msm_dp_mst->max_streams = max_streams;
> 
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry