On Wed, 2019-10-23 at 16:42 +1100, Michael Ellerman wrote: > > Right, it seems of_dma_is_coherent() has baked in the assumption that > devices are non-coherent unless explicitly marked as coherent. > > Which is wrong on all or at least most existing powerpc systems > according to Ben. This is probably broken on sparc(64) as well and whatever else uses DT and is an intrinsicly coherent architecture (did we ever have DT enabled x86s ? Wasn't OLPC such a beast ?). I think this should have been done the other way around and default to coherent since most traditional OF platforms are coherent, and you can't just require those DTs to change. > > Any ideas from the PPC maintainers? > > Fixing it at the source seems like the best option to prevent future > breakage. > > So I guess that would mean making of_dma_is_coherent() return true/false > based on CONFIG_NOT_COHERENT_CACHE on powerpc. > > We could do it like below, which would still allow the dma-coherent > property to work if it ever makes sense on a future powerpc platform. > > I don't really know any of this embedded stuff well, so happy to take > other suggestions on how to handle this mess.
