Re: [PATCH RFC v3 0/7] Async Flip in Atomic ioctl corrections

["Murthy, Arun R" <arun.r.murthy@intel.com>]

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On 09-01-2026 16:52, Michel Dänzer wrote:
> On 1/9/26 12:07, Murthy, Arun R wrote:
>>> From: Michel Dänzer<michel.daenzer@mailbox.org>
>>> On 1/8/26 10:43, Arun R Murthy wrote:
>>>> struct drm_crtc_state {
>>>>           /**
>>>>            * @async_flip:
>>>>            *
>>>>            * This is set when DRM_MODE_PAGE_FLIP_ASYNC is set in the legacy
>>>>            * PAGE_FLIP IOCTL. It's not wired up for the atomic IOCTL
>>>> itself yet.
>>>>            */
>>>>           bool async_flip;
>>>>
>>>> In the existing code the flag async_flip was intended for the legacy
>>>> PAGE_FLIP IOCTL. But the same is being used for atomic IOCTL.
>>>> As per the hardware feature is concerned, async flip is a plane
>>>> feature and is to be treated per plane basis and not per pipe basis.
>>>> For a given hardware pipe, among the multiple hardware planes, one can
>>>> go with sync flip and other 2/3 can go with async flip.
>>> FWIW, this kind of mix'n'match doesn't seem useful with current UAPI, since no
>>> new commit can be made for the async plane(s) before the previous commit for
>>> the sync plane(s) has completed, so the async plane(s) can't actually have
>>> higher update rate than the sync one(s).
>> That’s right, such mix and match flips will still consume vblank time for flipping.
> Does a plane property really make sense for this then?

As per the hardware this async flip is per plane basis and not per crtc. 
Looking into the corrections in the display driver, the flag that we are 
using async_flip which is defined in drm_crtc_state has been commented 
saying this is to be used with legacy page_flip ioctl.
When support for async was added in atomic_ioctl, approach was taken so 
as to get it working with minimal changes.
Not that I am trying to clean up this. Recently AMD added async support 
on overlays as well for which  few other hacks were added. The checks 
that we do for async flip were all done in place of copy the 
objs/properties, but it actually is supposed to be done in the 
check_only() part of the drm core code. This was the limitation with the 
existing implementation.
As per hardware the async flip is associated with the plane, hence 
changing it to a plane property. Have taken precautions to not break the 
existing workflow.

This change will make the driver more clean for async flips and will 
give path for enabling more hardware features pertaining to async flip 
supported by the hardware.


>
>> This series doesn’t solve that, but rather accommodate multiple plane async flips in an atomic ioctl and allowing disabling of a sync plane which is already enabled. There has been a long discussion in the gitlab(https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13834) on this.
> AFAICT that's a false-positive rejection of commits which don't actually change cursor plane state.

https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/13834#note_2855843

Thanks and Regards,
Arun R Murthy
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