On Monday, October 10th, 2022 at 10:19, Pekka Paalanen <ppaalanen@xxxxxxxxx> wrote:
> I'm completely clueless about this API.
No worries!
> > +/**
> > + * struct drm_syncobj_timeline_register_eventfd
> > + *
> > + * Register an eventfd to be signalled when a timeline point completes. The
> > + * eventfd counter will be incremented by one.
>
> Sounds nice.
>
> Since the action is to increment the counter by one, does it mean it
> will be possible to wait for a bunch of completions and have the
> eventfd poll return only when they have all signaled?
It is possible to perform the IOCTL multiple times with the same eventfd, but
eventfd semnatics would wake up user-space each time any timeline point
completes.
> > + */
> > +struct drm_syncobj_timeline_register_eventfd {
> > + __u32 handle;
>
> Handle of what?
drm_syncobj handle
> > + __u32 flags;
>
> What flags are allowed? Must be zero for now?
Same flags as the wait IOCTL.
Must be WAIT_AVAILABLE for now, but I'll implement the zero case as well (see
TODO).
> > + __u64 point;
>
> Is this some Vulkan thingy?
It's a drm_syncobj timeline thing. The timeline contains multiple sync points.
> > + __s32 fd;
>
> I guess the userspace needs to create an eventfd first, and pass it as
> the argument here? This is not creating a new eventfd itself?
Correct
> > + __u32 pad;
>
> Must be zero?
Indeed.
I'll spell out these requirements explicitly in the next version.
