On Wed, Dec 21, 2011 at 05:27:16PM +0000, Arnd Bergmann wrote: > On Tuesday 20 December 2011, Daniel Vetter wrote: > > 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. Yeah, that's actually what I wanted to say, but failed at ... Another thing is that at least for i915, _writecombine isn't what we want actually because: - It won't work anyway cause i915 maps stuff cached and does the flushing itself and x86 PAT doesn't support mixed mappings (kinda like arm). - It isn't actually enough, there's another hidden buffer between the memory controller interface and the gpu that i915 manually flushes (because even a readback on a wc mapping doesn't flush things in there). So I assume we'll have plenty of funny beating out a good api for cpu access ;-) Cheers, Daniel -- Daniel Vetter Mail: daniel@xxxxxxxx Mobile: +41 (0)79 365 57 48 -- 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>