On Tuesday 20 December 2011, Daniel Vetter wrote: > > I'm thinking for a first version, we can get enough mileage out of it by saying: > > 1) only exporter can mmap to userspace > > 2) only importers that do not need CPU access to buffer.. Ok, that sounds possible. The alternative to this would be: 1) The exporter has to use dma_alloc_coherent() or dma_alloc_writecombine() to allocate the buffer 2. Every user space mapping has to go through dma_mmap_coherent() or dma_mmap_writecombine() We can extend the rules later to allow either one after we have gained some experience using it. > > This way we can get dmabuf into the kernel, maybe even for 3.3. I > > know there are a lot of interesting potential uses where this stripped > > down version is good enough. It probably isn't the final version, > > maybe more features are added over time to deal with importers that > > need CPU access to buffer, sync object, etc. But we have to start > > somewhere. > > I agree with Rob here - I think especially for the coherency discussion > some actual users of dma_buf on a bunch of insane platforms (i915 > qualifies here too, because we do some cacheline flushing behind everyones > back) would massively help in clarifying things. Yes, agreed. > It also sounds like that at least for proper userspace mmap support we'd > need some dma api extensions on at least arm, and that might take a while > ... I think it's actually the opposite -- you'd need dma api extensions on everything else other than arm, which already has dma_mmap_coherent() and dma_mmap_writecombine() for this purpose. Arnd -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>