[igt-dev] [PATCH i-g-t] tests/kms_plane_lowres: Test only with one plane

[Kahola, Mika]

On Fri, 2020-01-17 at 15:15 +0200, Petri Latvala wrote:
> On Fri, Jan 17, 2020 at 02:44:40PM +0200, Kahola, Mika wrote:
> > On Fri, 2020-01-17 at 14:13 +0200, Petri Latvala wrote:
> > > On Fri, Jan 17, 2020 at 11:17:49AM +0200, Mika Kahola wrote:
> > > > The test is intended to test resolution changes from higher to
> > > > lower and back. We can test this with only one plane and we
> > > > don't
> > > > need to run through all planes. This will save significant
> > > > amount
> > > > of test execution time.
> > > > 
> > > > Fix for
> > > > Bugzilla: https://gitlab.freedesktop.org/drm/intel/issues/899
> > > 
> > > I'm having a hard time understanding how this change fixes this
> > > issue.
> > 
> > For some reason crc's don't match if we loop through multiple
> > overlay
> > planes. The reference image has primary, first overlay and cursors
> > plane. Crc already fails if we compare the reference with the image
> > having primary, second overlay and cursor plane. This I have been
> > testing with TGL.
> 
> 
> Commit message talks about saving test execution time but this
> explanation is about working around failures.
Right. I should have been more verbal about the commit message. On TGL
running a single subtest takes ~15s with one plane of each type. If we
loop through all planes, it takes ~55s.

> 
> What is actually broken and is this working around an issue or hiding
> it? Is it always the same plane combination failing, every test
> round?
> 
> (Am I reading the test wrong though, as far as I can see there's just
> two planes in use at a time, primary and one other...)
That's true. The crc's are ok with overlay plane[0] but has a mismatch
on the round plane[1]. Should we draw references too with all the
overlay planes instead? Any suggestions how to handle this?

Originally, we tested only with the first overlay plane. This is not
about testing the plane but more on testing resolution changes. That's
why I suggested to take a step back and test only with one plane.

> At the very least one plane of each type should be tested instead of
> just the first non-primary.
> 
>