Re: [PATCH 3/3] drm/radeon: add userfence IOCTL

[Jerome Glisse <j.glisse@gmail.com>]

On Mon, Apr 13, 2015 at 08:26:05PM +0200, Christian König wrote:
> On 13.04.2015 19:51, Jerome Glisse wrote:
> >On Mon, Apr 13, 2015 at 07:23:34PM +0200, Daniel Vetter wrote:
> >>On Mon, Apr 13, 2015 at 04:52:17PM +0200, Christian König wrote:
> >>>From: Christian König <christian.koenig@amd.com>
> >>>
> >>>WIP patch which adds an user fence IOCTL.
> >>>
> >>>Signed-off-by: Christian König <christian.koenig@amd.com>
> >>I've discussed userspace fences a lot with Jerome last XDC, so here's my
> >>comments:
> >>
> >>My primary concern with mid-batch fences is that if we create real kernel
> >>fences (which might even escape to other places using android syncpts or
> >>dma-buf) then we end up relying upon correct userspace to not hang the
> >>kernel, which isn't good.
> >Yes i agree on that, solution i propose make sure that this can not happen.
> 
> What if we want to base a GPU scheduler and Android sync points on that
> functionality? E.g. it might be necessary to create "struct fence" objects
> which are based on the information from userspace.
> 
> Would that be possible or would we run into issues?

Well i would not like that, but i do not like Android code much, but you
could use the same code as i show in my other email and just have the
android fence struct take a reference on the BO where the fence is. Then
using same code to check status.

Obviously there should be timeout as there is no way for the kernel to
know if such fence will ever signal.

Cheers,
Jérôme
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