[PATCH 1/3] drm/etnaviv: submit support for in-fences

[Philipp Zabel]

On Fri, 2017-03-17 at 11:00 -0300, Gustavo Padovan wrote:
> 2017-03-16 Philipp Zabel <p.zabel at pengutronix.de>:
> 
> > Hi Gustavo,
> > 
> > On Mon, 2017-03-13 at 14:37 -0300, Gustavo Padovan wrote:
> > [...]
> > > I was thinking on some function that would iterate over all fences in
> > > the fence_array and check their context. The if we find our own gpu
> > > context in there we fail the submit.
> > 
> > Why would we have to fail if somebody feeds us our own fences? Wouldn't
> > it be enough to just wait if there are foreign fences in the array?
> 
> You don't need to fail necessarily. In my mind I had the use case that
> maybe some driver could deadlock waiting for his own fence. What you
> do with the information that the array has it a fence with the driver's
> context is entirely up to the driver to decide.
[...]
> If we don't mind having fences with our own context, why should we check
> them?

My understanding was that for foreign fences we have to wait, for
example before resolving into a framebuffer that is still being scanned
out. But if we are fed fences from our own context, we can just ignore
them because etnaviv just has a single command queue, so anything
waiting for a fence from our own context will be queued after that fence
is signaled anyway.

regards
Philipp