Re: [PATCH] arm64: Enable PCI write-combine resources under sysfs

Benjamin Herrenschmidt
2020-09-16T22:15:27Z

On Wed, 2020-09-16 at 18:00 +0100, Catalin Marinas wrote:
> > That we don't know but if a prefetchable BAR can't tolerate read
> > side effects this would be already a problem on eg x86 - that's
> > the best we can hope for given the current PCI specs.
> >
> > +1 on normal NC. The only open point is whether we should make
> > arch_can_pci_mmap_wc() return false on platforms like TX2.
>
> I lost track in this thread whether it matters. TX2 would need Device
> GRE for optimal performance but the kernel doesn't currently provide
> it anyway. We could expose a new memory type, aligned_wc ;).

Or ignore TX2 :-) Though Lorenzo has a point about making it return
false for arch_can_pci_mmap_wc() if we really care enough.

Cheers,
Ben.