[Linaro-mm-sig] [RFC] Synchronizing access to buffers shared with dma-buf between drivers/devices

[Daniel Vetter]

On Sat, Jun 9, 2012 at 12:22 AM, Erik Gilling <konkers at android.com> wrote:
> The current linux graphics stack does not allow synchronization
> between the GPU and a camera/video decoder.  When we've seen people
> try to support this behind the scenes, they get it wrong and introduce
> bugs that can take weeks to track down.  As stated in the previous
> email, one of our goals is to centrally manage synchronization so that
> it's easer for people bringing up a platform to get it right.

I agree that letting everyone reinvent the wheel isn't the best idea
for cross-device sync - people will just get it wrong way too often.
I'm not convinced yet that doing it with explicit sync points/fences
and in userspace is the best solution. dri2/gem all use implicit sync
points managed by the kernel in a transparent fashion, so I'm leaning
towards such a sulotion for cross-device sync, too. Imo the big upside
of such an implicitly sync'ed approach is that it massively simplifies
cross-process protocols (i.e. for the display server).

So to foster understanding of the various requirements and use-cases,
could you elaborate on the pros and cons a bit and explain why you
think explicit sync points managed by the userspace display server is
the best approach for android?

Yours, Daniel
-- 
Daniel Vetter
daniel.vetter at ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch