[PATCH] iommu: Tidy up io-pgtable dependencies

[Conor Dooley]

On Mon, Jan 16, 2023 at 10:56:21AM +0000, Robin Murphy wrote:
> On 2023-01-13 22:17, Conor Dooley wrote:
> > Hey Robin,
> > 
> > On Thu, Jan 12, 2023 at 07:59:47PM +0000, Robin Murphy wrote:
> > > Some io-pgtable implementations, and thus their users too, carry a
> > > slightly odd dependency to get around the GENERIC_ATOMIC64 version of
> > > cmpxchg64() often failing to compile. Since this is a functional
> > > dependency, it's a bit misleading and untidy to tie it explicitly to
> > > COMPILE_TEST while assuming that it's also implied by the other
> > > platform/architecture options. Make things clearer by separating these
> > > functional dependencies into distinct statements from those controlling
> > > visibility, and since they do look a bit non-obvious to the uninitiated,
> > > also commenting them for good measure.
> > > 
> > > Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> > > ---
> > >   drivers/iommu/Kconfig | 18 ++++++++++++------
> > >   1 file changed, 12 insertions(+), 6 deletions(-)
> > 
> > >   config IPMMU_VMSA
> > >   	bool "Renesas VMSA-compatible IPMMU"
> > > -	depends on ARCH_RENESAS || (COMPILE_TEST && !GENERIC_ATOMIC64)
> > > +	depends on ARCH_RENESAS || COMPILE_TEST
> > > +	depends on !GENERIC_ATOMIC64	# for IOMMU_IO_PGTABLE_LPAE
> > >   	select IOMMU_API
> > >   	select IOMMU_IO_PGTABLE_LPAE
> > >   	select ARM_DMA_USE_IOMMU
> > 
> > This is a fix for the broken riscv32 allmodconfig stuff that Palmer
> > reported, right?
> 
> Indirectly - that made it clear that the whole area was worth cleaning up in
> general, so I did this expecting to rebase it around one of the other fix
> patches, but none of those seem to have gone anywhere.
> 
> In the meantime I guess it might now be simplest to apply Palmer's config
> workaround if you want something more expedient.

I amn't too bothered about workarounds, I don't build 32-bit allmodconfig.
I was hoping that an actual fix would show up, but it's clear that
no-one other than Palmer does actively build it.

Do you mind if I rip this part out of here & submit it standalone,
since no-one seems to be bothered by the failure enough to re-submit
your suggestion from the original threads?

Thanks,
Conor.

> > https://lore.kernel.org/all/20221214180409.7354-1-palmer@rivosinc.com/
> > 
> > I did a dfn:drivers/iommu/Kconfig search on lore & saw this, but AFAICT
> > the patch was applied to next rather than fixes.
> > 
> > Apologies if I'm off here, I have had that report in my follow-up-on
> > queue for a while & since Christmas happened in between I've lost track
> > of when the build failure was introduced.
> > 
> > Last I remember, Guo Ren sent a patch that was not to your liking, but I
> > didn't see anything after that.

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