On Tue, Nov 12, 2019 at 3:06 PM Christoph Hellwig <hch@xxxxxx> wrote: > On Tue, Nov 12, 2019 at 02:04:16PM +0100, Daniel Vetter wrote: > > Wut ... Maybe I'm missing something, but from how we use mtrr in other > > gpu drivers it's a) either you use MTRR because that's all you got or > > b) you use pat. Mixing both sounds like a pretty bad idea, since if > > you need MTRR for performance (because you dont have PAT) then you > > can't fix the wc with the PAT-based ioremap_uc. And if you have PAT, > > then you don't really need an MTRR to get wc. > > > > So I'd revert this patch from Luis and ... > > Sounds great to me.. > > > ... apply this one. Since the same reasoning should apply to anything > > that's running on any cpu with PAT. > > Can you take a look at "mfd: intel-lpss: Use devm_ioremap_uc for MMIO" > in linux-next, which also looks rather fishy to me? Can't we use > the MTRR APIs to override the broken BIOS MTRR setup there as well? Hm so that's way out of my knowledge, but I think mtrr_cleanup() was supposed to fix up messy/broken MTRR setups by the bios. So maybe they simply didn't enable that in their .config with CONFIG_MTRR_SANITIZER. An explicit cleanup is currently not possible for drivers, since the only interface exported to drivers is arch_phys_wc_add/del (which short-circuits if pat works since you don't need mtrr in that case). Adding everyone from that commit, plus Luis. Drivers really shouldn't assume/work around the bios setting up superflous/wrong MTRR. > With that we could kill ioremap_uc entirely. So yeah removing that seems definitely like the right thing. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
