Re: [PATCH igt] lib/kms: Force a full reprobe if we find a bad link

[Martin Peres <martin.peres@linux.intel.com>]

On 31/05/17 15:42, Chris Wilson wrote:
> On Wed, May 31, 2017 at 01:40:00PM +0300, Martin Peres wrote:
>> On 26/05/17 14:48, Chris Wilson wrote:
>>> If we do a shallow probe of the connector and it reports the link failed
>>> previous (link-status != GOOD), force a full probe of the connector to
>>> give the kernel a chance to validate the mode list.
>>
>> Sounds good, but will this make the tests SKIP if no modes are available?
> 
> I'm actually not sure what will happen if the mode is removed. I think
> the tests are just using the first mode in the list? At the moment I
> hope just to stop turning a single failure into many, it is still a bug
> that the link training failed and was not recovered. Alternatively, we
> can ask why isn't the kernel taking the corrective action when presented
> with a new setcrtc?

No, this is not a kernel bug, it is a failure that the userspace has to 
handle because the kernel can't do shit about this.

> 
> I'm not sure what the correct approach here should be, just what is the
> contract the kernel is expecting of userspace? Should that contract
> apply to new clients unaware of the earlier error?

Right, IGT assumes that if a mode is already set, it can be set again. 
However, this assumption has been broken when the link-status patches 
landed.

On a hotplug event, IGT should do a full reprobe, select one mode from 
the list and use it. If no modes can be set and the test is trying to 
set one, then the test should just SKIP.
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