I see no request for being able to mix sync & async plane updates in a single commit.

Sorry maybe I might be creating more confusion or my words are not
giving clarity.

Let me try to put it in simple words.
The
comment(https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13834#note_2857640)
from Xaver says that disabling of cursor plane along with a sync flip
should work.
Uma in the
comment(https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13834#note_2863599)
has acknowledged the changes.

That's about a plane that was previously already disabled by a
non-async atomic commit. The issue is about the async commit failing
in a sequence like this:
- disable cursor plane in sync commit
- disable cursor plane in async commit + flip on the primary plane

I would *in general* like to be able to use the cursor plane while
doing async flips on the primary one, but I think doing that requires
more discussion on the high level API design first.

https://lore.kernel.org/dri-devel/16c6c70f-0b89-4a41-8e3c-835a9ce296d5@intel.com/

Thanks and Regards,
Arun R Murthy
--------------------