linux-kernel - Re: [PATCH] iommu/ipmmu-vmsa: Drop LPAE Kconfig dependency

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Date:	Mon, 19 Oct 2015 09:42:14 +0300
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	iommu@...ts.linux-foundation.org,
	laurent.pinchart+renesas@...asonboard.com, geert+renesas@...der.be,
	linux-sh@...r.kernel.org, joro@...tes.org,
	linux-kernel@...r.kernel.org, horms+renesas@...ge.net.au
Subject: Re: [PATCH] iommu/ipmmu-vmsa: Drop LPAE Kconfig dependency

Hi Magnus,

Thank you for the patch.

On Monday 19 October 2015 12:02:53 Magnus Damm wrote:
> From: Magnus Damm <damm+renesas@...nsource.se>
> 
> Neither the ARM page table code enabled by IOMMU_IO_PGTABLE_LPAE
> nor the IPMMU_VMSA driver actually depends on ARM_LPAE, so get
> rid of the dependency.
>
> Tested with ipmmu-vmsa on r8a7794 ALT and a kernel config using:
>  # CONFIG_ARM_LPAE is not set

The driver only supports the 40-bits page table format for now, hence the 
dependency on LPAE, but it indeed seems that the dependency is bogus. As long 
as the 8 MSBs of the translated address are all 0 I assume the output 40-bit 
address is usable on a 32-bit physical address system.

How have you tested the patch ?

> Signed-off-by: Magnus Damm <damm+renesas@...nsource.se>
> ---
> 
>  drivers/iommu/Kconfig |    1 -
>  1 file changed, 1 deletion(-)
> 
> --- 0001/drivers/iommu/Kconfig
> +++ work/drivers/iommu/Kconfig	2015-10-18 14:58:09.080513000 +0900
> @@ -324,7 +324,6 @@ config SHMOBILE_IOMMU_L1SIZE
> 
>  config IPMMU_VMSA
>  	bool "Renesas VMSA-compatible IPMMU"
> -	depends on ARM_LPAE
>  	depends on ARCH_SHMOBILE || COMPILE_TEST
>  	select IOMMU_API
>  	select IOMMU_IO_PGTABLE_LPAE

-- 
Regards,

Laurent Pinchart

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