[Intel-gfx] [PATCH i-g-t 1/2] tests/chamelium: Skip suspend/resume test with unreliable hotplug event

[Paul Kocialkowski]

On Tue, 2017-07-18 at 22:21 +0100, Chris Wilson wrote:
> Quoting Paul Kocialkowski (2017-07-18 16:16:26)
> > It may occur that a hotplug uevent is detected at resume, even
> > though it
> > does not indicate that an actual hotplug happened. This is the case
> > when
> > link training fails on any other connector.
> > 
> > There is currently no way to distinguish what connector caused a
> > hotplug
> > uevent, nor what the reason for that uevent really is. This makes it
> > impossible to find out whether the test actually passed or not.
> 
> And you may get more than one and then this skips even though the test
> passed. Looks like the patch is overcompensating. What you can do is
> repeat the test a few times, and then look at all the different errors
> you get. If the connector remains (no mst disappareance) once it goes
> bad, it should remain bad and so not generate any new uevent. Or you
> only repeat the test whilst link_status[old] != link_status[new].

I am not sure it is really desirable to repeat the test until we are
fairly certain it succeeds. This involves suspend/resume, that is
already long enough as it is.

Also, a uevent will be generated everytime link training fails,
regardless of whether it was already failing before (I just tested that
to make sure). In my case, it's due to a DP-VGA bridge that will
consistently fail link training in the first seconds after resume.

So this is actually even worse that I thought, because there is no way
to find out that this is why a uevent was generated if the link status
was already bad before.

So I don't see how we can manage with the current information at
disposal.

My main point here is that we need more information about what's going
on than simply "HOTPLUG=1". These patches demonstrate that working
around the lack of information is a pain for testing purposes and can
only leads to semi-working hackish workarounds.

Do you agree that this is what the problem really is?

-- 
Paul Kocialkowski <paul.kocialkowski at linux.intel.com>
Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo, Finland