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

[Daniel Vetter]

On Tue, Aug 5, 2014 at 4:59 PM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
>> 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.
>
> Given that I've got a new execbuf coming too, I just wanted to keep
> them separate.  Any compelling reason to try to wedge it into execbuf?

The new execbuf is for svm, and there we obviously need fences. But we
also need proper fence support everywhere else (hence also the comment
that we need support for fences in drm events).

>> 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.
>
> Except for actually using the fences...

Actually no, nothing needed - drivers already signal drm_events in all
the right places, so we really only need to change
drm_send_vblank_event. And ofc we need to rework the code in the
pageflip/atomic/vblank_wait ioctl code in the drm core to create a
fence (and return it to userspace) instead of a normal drm event.

>> 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.
>
> Yeah I think that was mentioned in the commit.  Once Chris's stuff
> lands this should look even simpler.
>
>> 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.
>
> Yep, I'm hoping Chris has a use for this too in the DDX.  I think
> Wayland wants it too.

Well since syncpts are originally from Android I'd really prefere an
Android based implementation - otherwise we might create something by
accident that's not suitable for Android.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch