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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Jan 20, 2020 at 02:02:08PM +0200, Petri Latvala wrote:
> On Fri, Jan 17, 2020 at 04:35:37PM +0200, Kahola, Mika wrote:
> > 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.
> 
> Ok fair enough.
> 
> > > 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.
> 
> 
> The thumb rule is that we have a test case for all different
> behaviours of the driver, and incidentally for different behaviours of
> the hardware because the kernel is supposed to handle the
> differences. I suppose the pertinent question here is: Does the driver
> have different code paths for resolution changes for different plane
> usage?

I would expect that using any subset of HDR planes (first three
planes) + cursor to produce the same crc. The crc could be different
if any SDR planes are used since we have to instruct the hw to go
through the non-HDR blending path. If the test already fails with
some HDR planes then feels like there is an actual problem somewhere.

-- 
Ville Syrjälä
Intel
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