[igt-dev] [PATCH i-g-t 0/5] Fix mode selection for 2x tests

[Imre Deak]

On Wed, Apr 14, 2021 at 08:37:40PM +0200, Daniel Vetter wrote:
> > > > > [...]
> > > > > Uh this is really not how kms is supposed to work. There are _tons_ of
> > > > > reasons why 2 crtc at the same time wont work, mst bw constraint is
> > > > > just one.
> > > > > 
> > > > > If you want to fix this, this should be fixed with atomic TEST_ONLY
> > > > In fact, we are doing the same in this series.
> > > > 
> > > > By parsing the PATH connector prop, igt_output_refresh() will update the
> > > > link_group_id field for each connector [1]. 
> > > > 
> > > > Each individual (Nx)-test will identify the connectors those are sharing
> > > > the MST bw (by reading the link_group_id field in igt_output_t), and call
> > > > the helper to find the suitable modes [2].
> > > > 
> > > > A helper function iterates through those N output/mode combinations. And
> > > > find the combination using the most BW by ATOMIC_TEST_ONLY and returned
> > > > to the test [3].
> > > > 
> > > > Am I missing anything?
> > > 
> > > Using TEST_ONLY sounds good. Trying to do clever filtering with PATH
> > > property before you call TEST_ONLY is not good. You should check with
> > > TEST_ONLY in general, not just when the path property indicates that the
> > > dp output is shared.
> > 
> > I think it would still make sense to find the working config first on
> > outputs sharing a link bandwidth with TEST_ONLY and only then find the
> > config with all required outputs included in the TEST_ONLY commit,
> > starting with the modes found for outpus sharing a link. This is the way
> > you could find the maximum resolution that can be used on each output.
> 
> That sounds like a testcase to make sure we support at least 2 working
> modes on the same MST link. I'm not sure that really should be the generic
> solution thing, for that you just have to go around reducing resolutions
> until you've managed to light up enough outputs. So order doesn't
> matter really, aside from maybe a preference for same resolutions (due to
> clock sharing and even splits of fifos and that kind of stuff).
>
> Treating MST links specially just to light up a set of outputs still feels
> a bit wrong.

Imo we should test the most usual user scenario, which I assumed is the
max resolution on all connected displays. But this could be wrong and
any more complicated logic could be added as a follow up if needed. So
I'm also ok to ignore the link bandwidth sharing aspect.

> -Daniel
> 
> > 
> > > -Daniel
> > > 
> > > > 
> > > > [1]: https://patchwork.freedesktop.org/patch/427718
> > > > [2]: https://patchwork.freedesktop.org/patch/427720
> > > > [3]: https://patchwork.freedesktop.org/patch/427719
> > > >  N : 2,3,4,...
> > > > 
> > > > -Bhanu
> > > > > mode to figure out what works and what doesn't. Not by trying to
> > > > > re-implement the kernel's atomic_check configuration validation,
> > > > > because you just can't do that.
> > > > > 
> > > > > So nack on architectural reasons on this approach.
> > > > > -Daniel
> > > > > 
> > > > > >
> > > > > > Bhanuprakash Modem (5):
> > > > > >   lib/igt_kms: Add a support to read PATH connector property
> > > > > >   lib/igt_kms: Identify outputs that shares link bandwidth
> > > > > >   lib/igt_kms: helper to override the mode on all connectors
> > > > > >   tests/kms_frontbuffer_tracking: Fix mode selection for 2x tests
> > > > > >   tests/kms_cursor_legacy: Fix mode selection for 2x tests
> > > > > >
> > > > > >  lib/igt_kms.c                    | 71 ++++++++++++++++++++++++++++++++
> > > > > >  lib/igt_kms.h                    |  3 ++
> > > > > >  tests/kms_cursor_legacy.c        | 53 ++++++++++++++++++++++--
> > > > > >  tests/kms_frontbuffer_tracking.c | 35 ++++++++++++++++
> > > > > >  4 files changed, 159 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > --
> > > > > > 2.20.1
> > > > > >
> > > > > > _______________________________________________
> > > > > > igt-dev mailing list
> > > > > > igt-dev at lists.freedesktop.org
> > > > > > https://lists.freedesktop.org/mailman/listinfo/igt-dev
> > > > > 
> > > > > 
> > > > > 
> > > > > --
> > > > > Daniel Vetter
> > > > > Software Engineer, Intel Corporation
> > > > > http://blog.ffwll.ch
> > > 
> > > -- 
> > > Daniel Vetter
> > > Software Engineer, Intel Corporation
> > > http://blog.ffwll.ch
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch