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

[Modem, Bhanuprakash]

> From: Imre Deak <imre.deak at intel.com>
> Sent: Thursday, April 15, 2021 12:31 AM
> To: Daniel Vetter <daniel at ffwll.ch>
> Cc: Modem, Bhanuprakash <bhanuprakash.modem at intel.com>; Daniel Vetter
> <daniel.vetter at ffwll.ch>; Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>; IGT
> development <igt-dev at lists.freedesktop.org>
> Subject: Re: [igt-dev] [PATCH i-g-t 0/5] Fix mode selection for 2x tests
> 
> 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.

In simple words, just remove the MST specific stuff (link_group_id, PATH, etc...)
from this series, and each individual (Nx)-test should call the helper[1] to get
output/mode combo. Is my understanding correct?

[1] https://patchwork.freedesktop.org/patch/427719

> 
> > -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