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

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Message-ID: <54E24433.6070308@googlemail.com>
Date:	Mon, 16 Feb 2015 19:25:39 +0000
From:	Chris Clayton <chris2553@...glemail.com>
To:	Will Deacon <will.deacon@....com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs
 only



On 02/16/15 16:32, Will Deacon wrote:
> 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.
> 

There's no real problem except that, as I said, the prompt and the help text suggest that the config is relevant to ARM
architecture only. Same with the help text. When it popped up on x86_64, it was a surprise.

As you say, I can simply answer "N", but the prompt and the help need correcting, because for an ordinary Joe User like
me, it's misleading.


> Will
> 
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