[PATCH] drm: document how user-space should use link-status

[Simon Ser]

On Tuesday, June 2, 2020 9:38 AM, Pekka Paalanen <ppaalanen at gmail.com> wrote:

> Can it happen that there will be no modes left in
> the list?

Reading drm_helper_probe_single_connector_modes, this sounds unlikely
but possible.

This isn't specific to link-status though. This can be the case on a
regular hotplug uevent too.

> What if userspace is driving two connectors from the same CRTC, and only
> one connector gets link-status bad, what does it mean? Is the other
> connector still running as normal, as if the failed connector didn't
> even exist?
>
> That is mostly a question about what happens if userspace does not fix
> up the link-status=bad connector and does not detach it from the CRTC,
> but keeps on flipping or modesetting as if the failure never happened.
> I guess I could ask it about both a CRTC that has another connector
> still good, and a CRTC where the failed connector was the only one.
>
> Can I trust that if the other connector is in any way affected, it too
> will get link-status bad?

link-status is about link maintenance (e.g. DP link training), so I
think the other connector would be fine in this case. I'll add this to
the next version and let Daniel/Manasi comment if that's incorrect.