[Intel-gfx] [PATCH i-g-t] kms_rotation_crc: 90 degree flip test is not a stress test

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-08-03 15:33:54)
> 
> On 03/08/2017 15:19, Chris Wilson wrote:
> > Ultimately, is the path through the driver taken by each frame a good
> > enough metric to decide if the test has achieved its maximal coverage?
> 
> There should be a ton more coverage that we should add before calling it 
> maximal coverage. Like tiling changes between flips, which is currently 
> tested only for unrotated fbs. some rotation changes might also be 
> possible between flips?

That's fine. My question is more about can we assume driver coverage as
a reasonable guide for hw coverage, or rather how often can the hw do
something different when we take an identical path through the driver?

The worst offender I can think of is memory ordering, where the hw isn't
as strict as we would like and we spend lots of effort in trying to
enforce + check behaviour. But even then, our enforcement only takes a
few different patterns so the number of tests we need should be finite.
But I feel the trap there is by only testing what the driver does, we
never test what it does *not* do. And that is my conundrum how to find
the missing tests; how to reduce tests to achieve similar edge coverage
through the driver is easy enough (cf american fuzzy loop).
-Chris