Question on UAPI for fences

Hello everyone,

to allow concurrent buffer access by different engines beyond the multiple readers/single writer model that we currently use in radeon and other drivers we need some kind of synchonization object exposed to userspace.

My initial patch set for this used (or rather abused) zero sized GEM buffers as fence handles. This is obviously isn't the best way of doing this (to much overhead, rather ugly etc...), Jerome commented on this accordingly.

So what should a driver expose instead? Android sync points? Something else?

Please discuss and/or advise, Christian.