On Tue, Nov 12, 2019 at 03:26:35PM +0100, Daniel Vetter wrote: > 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. I had originally suggested to just make the driver build on x86, but an atlternative was to provide the call for the missing architecture. > 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). Right, the goal was to not call MTRR directly. > Adding everyone from that commit, plus Luis. Drivers really shouldn't > assume/work around the bios setting up superflous/wrong MTRR. Such things are needed, otherwise some systems may not boot... > > With that we could kill ioremap_uc entirely. > > So yeah removing that seems definitely like the right thing. I think this would be possible if we could flop ioremap_nocache() to UC instead of UC- on x86. Otherwise, I can't see how we can remove this by still not allowing direct MTRR calls. Luis _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
