I'm adding features to VKMS! What would you like to see?

[Daniel Stone]

Hi Jim,

On Fri, 29 Jul 2022 at 08:30, Jim Shargo <jshargo at chromium.org> wrote:
> TL;DR: I'm working on extending VKMS and wanted feedback from other
> compositor/wayland devs.

Awesome! :) Glad to see it, and yeah, I second everything Pekka said.
Having hotplug in particular would be really great.

> // Questions
>
>   - What VKMS features could help your testing the most?
>   - How much do you care about writeback buffer support vs CRC checks
> in tests atm?
>   - What kinds of bugs do you get around DRM/KMS?
>   - Any thoughts in general?

One thing I've really wanted is corner-case handling which just can't
be done in generic code. Weston is really aggressive at trying to get
things into planes, but we can only test those on actual systems with
particular semantics.

I'd love to be able to programmatically fake those to be able to check
our fallbacks in an automatic way. About the best idea I've come up
with for that is being able to attach an eBPF hook to atomic_check.
The absolute MVP would be no arguments and an errno return; if you
completely control the environment, then you can store a counter in a
map and return a particular error for the n'th attempt. But a better
one would allow you to inspect the properties on each object in the
atomic state, and also things like framebuffer attributes (dimensions,
format, modifier, etc) so you could take action accordingly.

Thanks for taking this on! Really looking forward to it.

Cheers,
Daniel