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

[Maxime Ripard]

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@xxxxxxxxxxx>
> >> Tested-by: Diederik de Haas <diederik@xxxxxxxxxxxxxx>  # NanoPC-T6 LTS, Rock 5B
> >> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxxxxxx>
> >> ---
> >>  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 :)

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);                                                                                                                                                                                                            

Maxime

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