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

[Yongxing Mou <yongxing.mou@oss.qualcomm.com>]

On 7/12/2026 6:44 PM, Dmitry Baryshkov wrote:
> 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.
> 
Got it.
>>   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.
> 
Here our original intent behind suppressing the hotplug was
that, under MST, hotplugs should be sent independently by the MST
framework, rather than being emitted along the IRQ handling path.

Following the extra_status approach you introduced, would it make sense
to let the bridge_connector layer distinguish between long pulses (HPD)
and short pulses (IRQ_HPD) -- a short pulse would not update
connector->status and would not emit a hotplug, only forwarding the
event to the bridge driver. Does this direction sound reasonable to
you?
> 
>>   }
>>   
>>   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.
> 
In MST case, MST DRM framework will send the discconnected hotplug by 
msm_dp_mst_display_set_mgr_state(&dp->msm_dp_display, false);.
>> +		}
>>   	}
>>   
>>   	pm_runtime_put_sync(&msm_dp_display->pdev->dev);
>>
>> -- 
>> 2.43.0
>>
>