Re: [PATCH 1/1] mm: EXPORT_SYMBOL_GPL(find_vm_area);

[Dan Williams <dan.j.williams@gmail.com>]

On Mon, Jan 11, 2016 at 5:00 AM, Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
> Hi Andrew,
>
> Andrew Morton wrote:
>> On Wed, 11 Nov 2015 15:06:24 +0200 Sakari Ailus <sakari.ailus@linux.intel.com> wrote:
>>
>>> find_vm_area() is needed in implementing the DMA mapping API as a module.
>>> Device specific IOMMUs with associated DMA mapping implementations should be
>>> buildable as modules.
>>>
>>> ...
>>>
>>> --- a/mm/vmalloc.c
>>> +++ b/mm/vmalloc.c
>>> @@ -1416,6 +1416,7 @@ struct vm_struct *find_vm_area(const void *addr)
>>>
>>>      return NULL;
>>>  }
>>> +EXPORT_SYMBOL_GPL(find_vm_area);
>>
>> Confused.  Who is setting CONFIG_HAS_DMA=m?
>>
>
> Apologies for the late reply --- CONFIG_HAS_DMA isn't configured as a
> module, but some devices are not DMA coherent even on x86. The existing
> x86 DMA mapping implementation doesn't quite work for those at the
> moment, and nothing prevents using another one (and as a module, in
> which case this patch is required).

Why not teach the DMA mapping api how to do cache management for such
devices?  Why would you need find_vm_area() exported?

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