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

[Daniel Vetter]

On Fri, Apr 9, 2021 at 1:39 PM Bhanuprakash Modem
<bhanuprakash.modem at intel.com> wrote:
>
> When two monitors connected through MST, the second monitor also
> tries to use the same mode. So two such modes may not fit into the
> link bandwidth.
>
> This series will find a combination of modes that fit into the BW.
>
> By parsing the PATH property, we can add a link_group_id field to
> igt_output_t to identify all connectors that shares the BW of the
> same link.
>
> Parsing the PATH property consists of finding all connectors with
> the same X prefix in the X-Y[-Z...] path property format and assigning
> a unique non-zero link_group_id to all such connectors. Connectors
> without a PATH property are not an MST output, so their link_group_id
> can be left at 0.
>
> IGT core helper would override the mode on all connectors that will
> be modeset by the next igt_display_commit() call in the test. These
> are all the connectors in igt_display_t that have a pending_pipe set
> by the test up to the point of calling this helper.
>
> Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem at intel.com>

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
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
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch