On Mon, 21 Jan 2019 at 18:55, Michel Dänzer <michel@xxxxxxxxxxx> wrote: > > On 2019-01-21 5:30 p.m., Ard Biesheuvel wrote: > > On Mon, 21 Jan 2019 at 17:22, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > >> Until that happens we should just change the driver ifdefs to default > >> the hacks to off and only enable them on setups where we 100% > >> positively know that they actually work. And document that fact > >> in big fat comments. > > > > Well, as I mentioned in my commit log as well, if we default to off > > unless CONFIG_X86, we may break working setups on MIPS and Power where > > the device is in fact non-cache coherent, and relies on this > > 'optimization' to get things working. > > FWIW, the amdgpu driver doesn't rely on non-snooped transfers for > correct basic operation (the scenario Christian brought up is a very > specialized use-case), so that shouldn't be an issue. > The point is that this is only true for x86. On other architectures, the use of non-cached mappings on the CPU side means that you /do/ rely on non-snooped transfers, since if those transfers turn out not to snoop inadvertently, the accesses are incoherent with the CPU's view of memory. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
