On Thu, 1 Mar 2012 16:36:00 +0100, Daniel Vetter <daniel.vetter at ffwll.ch> 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. -Chris -- Chris Wilson, Intel Open Source Technology Centre
