Re: Fence, timeline and android sync points

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

On Thu, Aug 14, 2014 at 09:16:02AM -0400, Rob Clark wrote:
> On Wed, Aug 13, 2014 at 1:07 PM, Jerome Glisse <j.glisse@gmail.com> wrote:
> > So this is fundamentaly different, fence as they are now allow random driver
> > callback and this is bound to get ugly this is bound to lead to one driver
> > doing something that seems innocuous but turn out to break heavoc when call
> > from some other driver function.
> 
> 
> tbh, that seems solvable by some strict rules about what you can do in
> the callback.. ie. don't do anything you couldn't do in atomic, and
> don't signal another fence.. off the top of my head that seems
> sufficient.
> 
> If the driver getting the callback needs to do more, then it can
> always schedule a worker..
> 
> But I could certainly see the case where the driver waiting on fence
> sets everything up before installing the cb and then just needs to
> write one or a couple regs from the cb.

Yes sane code will do sane things, sadly i fear we can not enforce sane
code everywhere especialy with out of tree driver and i would rather
force there hand to only allow sane implementation. Providing call back
api obviously allows them to do crazy stuff.

> 
> BR,
> -R