On Sat, Jan 2, 2021 at 1:35 PM Mario Kleiner mario.kleiner.de@gmail.com wrote:
I'm less sure about nouveau. It uses modifiers, but has atomic support only on nv50+ and that atomic support is off by default -- needs a nouveau.nouveau_atomic=1 boot parameter to switch it on. It seems to enable modifier support unconditionally regardless if atomic or not, see: https://elixir.bootlin.com/linux/v5.11-rc1/source/drivers/gpu/drm/nouveau/no...
Atm. nouveau doesn't assign a new format_info though, so wouldn't trigger this issue atm.
Note that pre-nv50, no modifiers exist. Also, drm_drv_uses_atomic_modeset() doesn't care whether the client is an atomic client or not. It will return true for nv50+ no matter what. nouveau_atomic=1 affects whether atomic UAPI is exposed. Not sure if this impacts your discussion.
Cheers,
-ilia