Documentation showing requirements on correct userspace DRM master behavior?

[Matt Hoosier]

I’m trying to find some sort of formal document showing the thou-shalts and
though-shalt-nots of userspace DRM applications’ interaction with the KMS
UAPI.

(For modern atomic commits, not the legacy modeset API.)

I’m interested in stuff like what minimum set of properties are required on
CRTCs or planes when activating or deactivating a connector. There’s very
good documentation at
https://www.kernel.org/doc/html/v4.14/gpu/drm-uapi.html showing the
expectations on drivers who implement KMS. But I didn’t find the equivalent
stuff that would show how to write a guaranteed-portable KMS application.

I find that it’s easy to write DRM masters that generally work on canonical
drivers like the integrated Intel GPUs, but show odd behaviors with forked
vendor DRM drivers. It would be really nice to be able to point to a spec
and say either that userspace is doing things by the book (so the bug must
be in the driver) or that userspace was unintentionally relying on
undefined driver behavior.

In practice, there are lots of working examples in libdrm or a reference
compositor like Wayland. But those don’t typically have inline comments to
differentiate between required and elective behavior.

Does anybody know whether something like that exists?

-Matt
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20240118/a2f1c789/attachment.htm>