linux-kernel - Re: [PATCH] iommu: PGTABLE

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Date:   Thu, 30 Mar 2023 09:31:27 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Conor Dooley <conor.dooley@...rochip.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        Conor Dooley <conor@...nel.org>,
        linux-riscv@...ts.infradead.org, geert+renesas@...der.be
Subject: Re: [PATCH] iommu: PGTABLE_LPAE is also for RISCV

Hi Conor,

On Thu, Mar 30, 2023 at 8:25 AM Conor Dooley <conor.dooley@...rochip.com> wrote:
> On Wed, Mar 29, 2023 at 11:01:05PM -0700, Randy Dunlap wrote:
> > On riscv64, linux-next-20233030 (and for several days earlier),
> > there is a kconfig warning:
> >
> > WARNING: unmet direct dependencies detected for IOMMU_IO_PGTABLE_LPAE
> >   Depends on [n]: IOMMU_SUPPORT [=y] && (ARM || ARM64 || COMPILE_TEST [=n]) && !GENERIC_ATOMIC64 [=n]
> >   Selected by [y]:
> >   - IPMMU_VMSA [=y] && IOMMU_SUPPORT [=y] && (ARCH_RENESAS [=y] || COMPILE_TEST [=n]) && !GENERIC_ATOMIC64 [=n]
> >
> > and build errors:
> >
> > riscv64-linux-ld: drivers/iommu/io-pgtable-arm.o: in function `.L140':
> > io-pgtable-arm.c:(.init.text+0x1e8): undefined reference to `alloc_io_pgtable_ops'
> > riscv64-linux-ld: drivers/iommu/io-pgtable-arm.o: in function `.L168':
> > io-pgtable-arm.c:(.init.text+0xab0): undefined reference to `free_io_pgtable_ops'
> > riscv64-linux-ld: drivers/iommu/ipmmu-vmsa.o: in function `.L140':
> > ipmmu-vmsa.c:(.text+0xbc4): undefined reference to `free_io_pgtable_ops'
> > riscv64-linux-ld: drivers/iommu/ipmmu-vmsa.o: in function `.L0 ':
> > ipmmu-vmsa.c:(.text+0x145e): undefined reference to `alloc_io_pgtable_ops'
> >
> > Add RISCV as an allowed ARCH dependency to fix these problems.
> >
> > Fixes: d286a58bc8f4 ("iommu: Tidy up io-pgtable dependencies")
> > Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> > Cc: Joerg Roedel <joro@...tes.org>
> > Cc: Will Deacon <will@...nel.org>
> > Cc: Robin Murphy <robin.murphy@....com>
> > Cc: iommu@...ts.linux.dev
> > Cc: Conor Dooley <conor@...nel.org>
> > Cc: linux-riscv@...ts.infradead.org
> > ---
> >  drivers/iommu/Kconfig |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff -- a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -32,7 +32,7 @@ config IOMMU_IO_PGTABLE
> >  config IOMMU_IO_PGTABLE_LPAE
> >       bool "ARMv7/v8 Long Descriptor Format"
>
> I'm probably missing something here, but why would we want to enable
> "ARMv7/v8 Long Descriptor Format" on RISC-V?

Indeed, we should not enable it, unless compile-testing.

> Would it not be better to make the Renesas depend on, rather than
> select the option? It does seem highly arch specific, and I feel like
> Geert previously mentioned that the RZ/Five (their RISC-V offering)
> didn't use it.

I think the IPMMU_VMSA dependency should gain

        depends on ARM || ARM64 || COMPILE_TEST

> >       select IOMMU_IO_PGTABLE
> > -     depends on ARM || ARM64 || COMPILE_TEST
> > +     depends on ARM || ARM64 || RISCV || COMPILE_TEST
> >       depends on !GENERIC_ATOMIC64    # for cmpxchg64()
> >       help
> >         Enable support for the ARM long descriptor pagetable format.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds