Re: [PATCH 3/5] drm/msm/dp: suppress bridge hotplug events during MST operation

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

On Mon, Jun 29, 2026 at 10:48:05PM +0800, Yongxing Mou wrote:
> The DP MST framework already generates the required hotplug events for
> MST topology changes.
> 
> Suppress connector hotplug event generation from the bridge connector
> path while MST is active, and continue propagating HPD notifications to
> the DP driver.
> 
> Signed-off-by: Yongxing Mou <yongxing.mou@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/display/drm_bridge_connector.c | 6 ++++--
>  drivers/gpu/drm/msm/dp/dp_display.c            | 9 ++++++++-

No, it can't go as this. The drm_bridge_connector part should have been
a part of the first patch.

>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_bridge_connector.c b/drivers/gpu/drm/display/drm_bridge_connector.c
> index 7334d6677604..82ed0dc450ab 100644
> --- a/drivers/gpu/drm/display/drm_bridge_connector.c
> +++ b/drivers/gpu/drm/display/drm_bridge_connector.c
> @@ -162,6 +162,7 @@ static void drm_bridge_connector_handle_hpd(struct drm_bridge_connector *drm_bri
>  {
>  	struct drm_connector *connector = &drm_bridge_connector->base;
>  	struct drm_device *dev = connector->dev;
> +	bool send_hotplug = true;
>  
>  	/*
>  	 * IRQ-only notification: extra_status carries the event but
> @@ -179,9 +180,10 @@ static void drm_bridge_connector_handle_hpd(struct drm_bridge_connector *drm_bri
>  	connector->status = status;
>  	mutex_unlock(&dev->mode_config.mutex);
>  
> -	drm_bridge_connector_hpd_notify(connector, status, extra_status, NULL);
> +	drm_bridge_connector_hpd_notify(connector, status, extra_status, &send_hotplug);
>  
> -	drm_kms_helper_connector_hotplug_event(connector);
> +	if (send_hotplug)
> +		drm_kms_helper_connector_hotplug_event(connector);

But now I can also see that the idea seems to be incorrect. You are
preventing the kernel from sending the events, but it doesn't really
matter. If connection status oscillates, then other components might
notice it even without the event being sent.


>  }
>  
>  static void drm_bridge_connector_hpd_cb(void *cb_data,
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index 6835c68fe510..bc93b566fbca 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1790,10 +1790,17 @@ void msm_dp_bridge_hpd_notify(struct drm_bridge *bridge,
>  			msm_dp_hpd_plug_handle(dp);
>  		} else {
>  			msm_dp_hpd_plug_handle(dp);
> +			/* mst_active is set in plug_handle; suppress SST hotplug */
> +			if (send_hotplug && msm_dp_display->mst_active)
> +				*send_hotplug = false;
>  		}
>  	} else {
> -		if (hpd_link_status == ISR_DISCONNECTED)
> +		if (!msm_dp_display->mst_active) {
>  			msm_dp_hpd_unplug_handle(dp);
> +		} else if (send_hotplug) {
> +			msm_dp_hpd_unplug_handle(dp);
> +			*send_hotplug = false;

Why? Disconnected events definitely should be reported further.

> +		}
>  	}
>  
>  	pm_runtime_put_sync(&msm_dp_display->pdev->dev);
> 
> -- 
> 2.43.0
> 

-- 
With best wishes
Dmitry

_______________________________________________
linux-amlogic mailing list
linux-amlogic@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-amlogic