linux-kernel - Re: [PATCH] iommu: prompt for IOMMU_IO_PGTABLE

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Message-ID: <20150216163247.GM10634@arm.com>
Date:	Mon, 16 Feb 2015 16:32:48 +0000
From:	Will Deacon <will.deacon@....com>
To:	Chris Clayton <chris2553@...glemail.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs only

Hi Chris,

On Sun, Feb 15, 2015 at 11:17:19AM +0000, Chris Clayton wrote:
> When running "make oldconfig" for an x86_64 kernel, I was prompted for a
> setting for IOMMU_IO_PGTABLE_LPAE. From the prompt and the help text it
> appears that this config item is relevant to ARMv7/v8 only. This patch
> prevents the prompt on non-ARM architectures. Compile tested building a
> cross-compiled x86_64 kernel in an x86 user space. The resultant kernel
> boots fine and I am running it now.
> 
> Fixes: e1d3c0fd701df831169b116cd5c5d6203ac07f70
> Cc: will.deacon@....com
> Signed-off-by: Chris Clayton <chris2553@...glemail.com>
> 
> --- linux/drivers/iommu/Kconfig.orig    2015-02-15 09:44:01.235927248 +0000
> +++ linux/drivers/iommu/Kconfig 2015-02-15 09:44:41.131926434 +0000
> @@ -22,6 +22,7 @@ config IOMMU_IO_PGTABLE
> 
>  config IOMMU_IO_PGTABLE_LPAE
>         bool "ARMv7/v8 Long Descriptor Format"
> +       depends on ARM || ARM64
>         select IOMMU_IO_PGTABLE
>         help
>           Enable support for the ARM long descriptor pagetable format.

What's the problem with this? The page-table code is intentionally
decoupled from the CPU architecture and having this boot-tested on x86
found some real bugs that I'm currently fixing. Sure, you probably don't
need this on your box, but it's not default y and you don't have to
select it.

Will
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