Re: [PATCH 12/14] dma-direct: handle the memory encryption bit in common code

[Robin Murphy]

On 19/03/18 15:24, Christoph Hellwig wrote:
> On Mon, Mar 19, 2018 at 03:19:04PM +0000, Robin Murphy wrote:
> > As a heads-up, I've just realised there's now a silent (but build-breaking)
> > conflict with the current arm64 queue brewing here, as we've unfortunately
> > had to reintroduce ARCH_HAS_PHYS_TO_DMA as a means of being safe against an
> > ugly architectural corner case - currently commit 1f85b42a691c ("arm64:
> > Revert L1_CACHE_SHIFT back to 6 (64-byte cache line size)") in -next.
>
> Please revert that arm64 commit.  This condition should be handled
> in common code as it is not arm specific.  And next time please CC
> the iommu list and dma-mapping maintainers before doing such a change.

There didn't seem enough justification to clutter up core SWIOTLB code 
with the ability to force bouncing on a per-device basis, but if you 
think there are real potential users out there then fair enough. For 
arm64, it's extremely unlikely that anyone will ever build a 
sufficiently wacky system to actually hit this code path; we really only 
implemented it for peace of mind per the letter of the architecture.

Robin.