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

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Date:   Thu, 30 Mar 2023 07:25:23 +0100
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     Randy Dunlap <rdunlap@...radead.org>
CC:     <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

Hey Randy,

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?
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.

Cheers,
Conor.

>  	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.
> 

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