On Fri, Mar 2, 2012 at 4:38 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote: > On Thu, 1 Mar 2012 16:36:00 +0100, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: >> Big differences to other contenders in the field (like ion) is >> that this also supports highmem, so we have to split up the cpu >> access from the kernel side into a prepare and a kmap step. >> >> Prepare is allowed to fail and should do everything required so that >> the kmap calls can succeed (like swapin/backing storage allocation, >> flushing, ...). >> >> More in-depth explanations will follow in the follow-up documentation >> patch. >> >> Changes in v2: >> >> - Clear up begin_cpu_access confusion noticed by Sumit Semwal. >> - Don't automatically fallback from the _atomic variants to the >> non-atomic variants. The _atomic callbacks are not allowed to >> sleep, so we want exporters to make this decision explicit. The >> function signatures are explicit, so simpler exporters can still >> use the same function for both. >> - Make the unmap functions optional. Simpler exporters with permanent >> mappings don't need to do anything at unmap time. > > Are we going to have to have a dma_buf->ops->begin_async_access(&me, dir) > variant for coherency control of rendering with an imported dma_buf? > There is also no concurrency control here between multiple importers > doing simultaneous begin_cpu_access(). I presume that is going to be a > common function across all exporters so the midlayer might offer a > semaphore as a library function and then the > dma_buf->ops->begin_cpu_access() becomes mandatory as at a minimum it > has to point to the default implementation. Initially 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. I expect, though, that one of the next steps is some sort of sync-object mechanism to supplement dmabuf BR, -R > -Chris > > -- > Chris Wilson, Intel Open Source Technology Centre > -- > 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 -- 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
