Re: [PATCH] iommu: Split out and tidy up Arm Kconfig

[Pranjal Shrivastava <praan@google.com>]

On Thu, Mar 20, 2025 at 02:21:28PM +0000, Robin Murphy wrote:
> There are quite a lot of options for the Arm drivers, still all buried
> in the top-level Kconfig. For ease of use and consistency with all the
> other subdirectories, break these out into drivers/arm. For similar
> clarity and self-consistency, also tweak the ARM_SMMU sub-options to use
> "if" instead of "depends", to match ARM_SMMU_V3. Lastly also clean up
> the slightly messy description of ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT as
> highlighted by Geert - by now we really shouldn't need commentary on
> v4.x kernel behaviour anyway - and downgrade it to EXPERT as the first
> step in the 6-year-old threat to remove it entirely.
> 
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/Kconfig     | 157 +-------------------------------------
>  drivers/iommu/arm/Kconfig | 144 ++++++++++++++++++++++++++++++++++
>  2 files changed, 145 insertions(+), 156 deletions(-)
>  create mode 100644 drivers/iommu/arm/Kconfig
> 

Thanks for this! It looks good.
I was able to toggle configs and build for arm64.

> +
> +config QCOM_IOMMUa
Nit: I don't have much context but:

1. Shall this be in .../arm/Kconfig? Is this an custom
implementation of some arm-smmu version? If yes, then maybe we can
update the help string while at it?

> +	# Note: iommu drivers cannot (yet?) be built as modules

2. I don't think this is true now? Shall we remove this comment?

> +	bool "Qualcomm IOMMU Support"
> +	depends on ARCH_QCOM || COMPILE_TEST
> +	depends on !GENERIC_ATOMIC64	# for IOMMU_IO_PGTABLE_LPAE
> +	select QCOM_SCM
> +	select IOMMU_API
> +	select IOMMU_IO_PGTABLE_LPAE
> +	select ARM_DMA_USE_IOMMU
> +	help
> +	  Support for IOMMU on certain Qualcomm SoCs.
> 

With the above nits:

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan