On Sun, 09 Oct 2022 14:40:14 +0000
Simon Ser <contact@xxxxxxxxxxx> wrote:
> Introduce a new DRM_IOCTL_SYNCOBJ_TIMELINE_REGISTER_EVENTFD IOCTL
> which signals an eventfd when a timeline point completes.
>
> This is useful for Wayland compositors to handle wait-before-submit.
> Wayland clients can send a timeline point to the compositor
> before the point has materialized yet, then compositors can wait
> for the point to materialize via this new IOCTL.
>
> The existing DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT IOCTL is not suitable
> because it blocks. Compositors want to integrate the wait with
> their poll(2)-based event loop.
>
> Signed-off-by: Simon Ser <contact@xxxxxxxxxxx>
> Cc: Jason Ekstrand <jason@xxxxxxxxxxxxxx>
> Cc: Daniel Vetter <daniel@xxxxxxxx>
> Cc: Christian König <christian.koenig@xxxxxxx>
> Cc: Bas Nieuwenhuizen <bas@xxxxxxxxxxxxxxxxxxx>
> Cc: Daniel Stone <daniel@xxxxxxxxxxxxx>
> Cc: Pekka Paalanen <ppaalanen@xxxxxxxxx>
> Cc: James Jones <jajones@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_internal.h | 3 +
> drivers/gpu/drm/drm_ioctl.c | 3 +
> drivers/gpu/drm/drm_syncobj.c | 113 +++++++++++++++++++++++++++++++--
> include/drm/drm_syncobj.h | 6 +-
> include/uapi/drm/drm.h | 15 +++++
> 5 files changed, 133 insertions(+), 7 deletions(-)
...
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 642808520d92..359e21414196 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -909,6 +909,20 @@ struct drm_syncobj_timeline_wait {
> __u32 pad;
> };
>
Hi,
I'm completely clueless about this API.
> +/**
> + * 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?
> + */
> +struct drm_syncobj_timeline_register_eventfd {
> + __u32 handle;
Handle of what?
> + __u32 flags;
What flags are allowed? Must be zero for now?
> + __u64 point;
Is this some Vulkan thingy?
> + __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?
> + __u32 pad;
Must be zero?
Thanks,
pq
> +};
> +
>
> struct drm_syncobj_array {
> __u64 handles;
> @@ -1095,6 +1109,7 @@ extern "C" {
> #define DRM_IOCTL_SYNCOBJ_QUERY DRM_IOWR(0xCB, struct drm_syncobj_timeline_array)
> #define DRM_IOCTL_SYNCOBJ_TRANSFER DRM_IOWR(0xCC, struct drm_syncobj_transfer)
> #define DRM_IOCTL_SYNCOBJ_TIMELINE_SIGNAL DRM_IOWR(0xCD, struct drm_syncobj_timeline_array)
> +#define DRM_IOCTL_SYNCOBJ_TIMELINE_REGISTER_EVENTFD DRM_IOWR(0xCE, struct drm_syncobj_timeline_register_eventfd)
>
> /**
> * DRM_IOCTL_MODE_GETFB2 - Get framebuffer metadata.
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