[PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs only

[PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs only

[Chris Clayton]

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@arm.com
Signed-off-by: Chris Clayton <chris2553@googlemail.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.

Re: [PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs only

[Will Deacon]

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@arm.com
> Signed-off-by: Chris Clayton <chris2553@googlemail.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

Re: [PATCH] iommu: prompt for IOMMU_IO_PGTABLE_LPAE on ARM archs only

[Chris Clayton]

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@arm.com
>> Signed-off-by: Chris Clayton <chris2553@googlemail.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
>