Re: [PATCH] drm/i915: Android sync points for i915 v2

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tue, 5 Aug 2014 18:08:16 +0200
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Tue, Aug 5, 2014 at 6:05 PM, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > On Tue, 5 Aug 2014 17:08:22 +0200
> > Daniel Vetter <daniel@ffwll.ch> wrote:
> >
> >> On Tue, Aug 5, 2014 at 4:59 PM, Jesse Barnes <jbarnes@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.
> >
> > Actually yes.  You get back a fence object and want to do something
> > with it, right?  That means new code.  Plus modifying current execbuf
> > users that want fences to pass in a flag.
> 
> This comment was specifically about vblank and pageflips, _not_ about
> execbuf. At least that's been what I've thought while writing the
> original mail and reading your reply. Looks like we have a
> misunderstanding here. Since for vblank and pageflip we really can do
> it all in the drm core.

I was thinking of userspace drivers and userspace, not kernel
internals...  that's the disconnect.