On Fri, Mar 2, 2012 at 23:53, Rob Clark <rob.clark@xxxxxxxxxx> wrote: > nitially the expectation was that userspace would not pass a buffer > to multiple subsystems for writing (or that if it did, it would get > the undefined results that one could expect).. so dealing w/ > synchronization was punted. Imo synchronization should not be part of the dma_buf core, i.e. userspace needs to ensure that access is synchronized. begin/end_cpu_access are the coherency brackets (like map/unmap for device dma). And if userspace asks for a gun and some bullets, the kernel should just deliver. Even in drm/i915 gem land we don't (and simply can't) make any promises about concurrent reads/writes/ioctls. > I expect, though, that one of the next steps is some sort of > sync-object mechanism to supplement dmabuf Imo the only reason to add sync objects as explicit things is to make device-to-device sync more efficient by using hw semaphores and signalling lines. Or maybe a quick irq handler in the kernel that kicks of the next device. I don't think we should design these to make userspace simpler. Cheers, Daniel -- Daniel Vetter daniel.vetter@xxxxxxxx - +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
