[Intel-gfx] [PATCH] drm/i915: Android sync points for i915 v2

[Daniel Vetter]

On Tue, Aug 5, 2014 at 1:18 AM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
> +#define DRM_IOCTL_I915_GEM_FENCE                       DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_FENCE, struct drm_i915_gem_fence)
>
>  /* Allow drivers to submit batchbuffers directly to hardware, relying
>   * on the security mechanisms provided by hardware.
> @@ -1066,4 +1068,25 @@ struct drm_i915_gem_userptr {
>         __u32 handle;
>  };
>
> +/**
> + * drm_i915_gem_fence - create a fence
> + * @fd: fd for fence
> + * @ctx_id: context ID for fence
> + * @flags: flags for operation
> + *
> + * Creates a fence in @fd and returns it to the caller.  This fd can be
> + * passed around between processes as any other fd, and can be poll'd
> + * and read for status.
> + *
> + * RETURNS:
> + * A valid fd in the @fd field or an errno on error.
> + */
> +struct drm_i915_gem_fence {
> +       __s32 fd;
> +       __u32 ctx_id;
> +       __u32 flags;
> +       __u32 pad;
> +       char name[32];
> +};
> +

This doesn't really look like the interface I'd expected. Imo we just
need to add a flag to execbuf so that userspace can tell the kernel to
create a fence for that execbuf, and switch one of the leftover rsvd
fields to __s32 as an outparam for the fd.

Then we need similar flags for vblank events and pageflips to do the
same (obviously those are drm core patches) and it's all there. That
should probably integrated as a special type of drm_event, so that
drivers don't need to change a single line of code.

Also this should be based on top of Chris' patch to refcount requests
and make them first-class structures. Then we can simply replace the
embedded struct kref with a struct fence, i.e. we'll always create a
fence, but only give userspace an fd handle for it when it asks for
it.

For merging there's a few things we need:
- Some open-source user, either the open-source android-ia project or
something else.
- The android syncpt stuff obviously needs to be de-staged. From my
side that means an ABI review of what's there (and getting the buy-in
from google guys if we need to change it) plus a full set of testcases
(if google doesn't already have something we could integrate easily).
Adding Greg and relevant people.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch