Re: [PATCH v10 22/69] drm/display: hdmi-state-helper: Sync SCDC state on hotplug

[Cristian Ciocaltea <cristian.ciocaltea@collabora.com>]

On 8/25/26 12:25 PM, Maxime Ripard wrote:
> On Thu, Aug 20, 2026 at 05:44:08PM +0300, Cristian Ciocaltea wrote:
>> On 8/20/26 11:53 AM, Maxime Ripard wrote:
>>> On Fri, Jul 31, 2026 at 07:19:29PM +0300, Cristian Ciocaltea wrote:
>>>> drm_atomic_helper_connector_hdmi_hotplug() does not currently
>>>> synchronize SCDC status on hotplug events, leaving the scrambler state
>>>> potentially inconsistent after (re)connect.
>>>>
>>>> Hook drm_connector_hdmi_sync_scdc() into both the connect and disconnect
>>>> paths, replacing the existing TODOs around missing scrambler handling.
>>>>
>>>> Tested-by: Maud Spierings <maud_spierings@hotmail.com>
>>>> Tested-by: Diederik de Haas <diederik@cknow-tech.com>  # NanoPC-T6 LTS, Rock 5B
>>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
>>>> ---
>>>>  drivers/gpu/drm/display/drm_hdmi_state_helper.c | 23 ++++++++++++++---------
>>>>  1 file changed, 14 insertions(+), 9 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>>>> index 4a93c279c9a7..3377ea936120 100644
>>>> --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>>>> +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
>>>> @@ -1205,13 +1205,16 @@ drm_atomic_helper_connector_hdmi_update(struct drm_connector *connector,
>>>>  					enum drm_connector_status status)
>>>>  {
>>>>  	const struct drm_edid *drm_edid;
>>>> +	int ret = 0;
>>>>  
>>>>  	if (status == connector_status_disconnected) {
>>>> -		// TODO: also handle scramber, HDMI sink disconnected.
>>>> -		drm_connector_hdmi_audio_plugged_notify(connector, false);
>>>> -		drm_edid_connector_update(connector, NULL);
>>>> -		drm_connector_cec_phys_addr_invalidate(connector);
>>>> -		return 0;
>>>> +		ret = drm_connector_hdmi_sync_scdc(connector, false, ctx);
>>>> +		if (ret != -EDEADLK) {
>>>> +			drm_connector_hdmi_audio_plugged_notify(connector, false);
>>>> +			drm_edid_connector_update(connector, NULL);
>>>> +			drm_connector_cec_phys_addr_invalidate(connector);
>>>> +		}
>>>
>>> If there's a deadlock, shouldn't we restart the whole sequence there?
>>
>> In that case we do already propagate -EDEADLK and let the callers
>> (drm_helper_probe_detect_ctx(), drm_helper_probe_single_connector_modes())
>> to ensure the sequence is restarted.
>>
>>> Ie, we should return ret all the time anyway? And if we do that, we
>>> should return ret for drm_edid_connector_update() too.
>>
>> Per .detect_ctx() contract, implementations shall return a drm_connector_status
>> value or -EDEADLK only.  On the other hand, .force_ctx() accepts any error code,
>> but the probe helpers just log it.  Hence returning anything else wouldn't
>> really have an impact on the functionality.
>>
>> Returning errors from drm_edid_connector_update() would potentially override
>> non-deadlock ones from sync_scdc().  Since both helpers already log their own
>> failures, I think it isn't worth the trouble.
>>
>>> Either way, a comment on why we're doing it this way would be nice.
>>
>> Indeed.  Would the following be too verbose?
>>
>> /*
>>  * The SCDC resync may reset the CRTC, which might involve aquiring
>>  * modeset locks.  If that fails, -EDEADLK is reported and the callers
>>  * passing a non-NULL @ctx drop the locks and restart the sequence
>>  * - see drm_helper_probe_detect_ctx() and
>>  * drm_helper_probe_single_connector_modes().
>>  *
>>  * The resync runs first, and the audio and CEC helpers only once the
>>  * link state has settled: the CRTC reset is a blocking commit, so on
>>  * success the pipeline is already up again, while on -EDEADLK nothing
>>  * has been resynced yet and the pending retry redoes everything.  This
>>  * keeps userspace from acting upon a link that is about to be reset.
>>  *
>>  * -EDEADLK is the only status gating the helpers below, as it is the
>>  * sole one guaranteeing a new run.  The other failures are merely
>>  * reported: .force_ctx() accepts any error code and the probe helpers
>>  * just log it, while .detect_ctx() has to swallow it, being only
>>  * allowed to return a drm_connector_status value or -EDEADLK.
>>  * Propagating the status of drm_edid_connector_update() on top would
>>  * therefore only make it compete with an earlier resync failure over a
>>  * value that triggers no recovery, the more so as both helpers already
>>  * log their own errors.
>>  */
> 
> You can tell your LLM to be more terse :)

That's actually the shortened form :-)

> 
> Something like the following would be enough:
> 
>   /*
>    * detect_ctx can only ever return an status or EDEADLK. Handle deadlocks, and report any !EDEADLK error.
>    */
>   ret = drm_connector_hdmi_sync_scdc(connector, false, ctx);
>   if (ret)
>      if (ret == -EDEADLK) {
>      	return ret;
>      } else {
>        drm_warn(connector->dev, "ignored error");
>      }
> 
>   drm_connector_hdmi_audio_plugged_notify(connector, false);                                                                                                                                                                                                    
>   ret = drm_edid_connector_update(connector, NULL);
>   if (ret)
>        drm_warn(connector->dev, "ignored error");
>   drm_connector_cec_phys_addr_invalidate(connector);                                                                                                                                                                                                            

Ack.

Thanks,
Cristian

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