Re: Linux 3.4-rc1

[Jerome Glisse <j.glisse@gmail.com>]

On Tue, Apr 3, 2012 at 5:07 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> On Tuesday 03 April 2012, Kyungmin Park wrote:
>> >
>> >  - DMA-mapping framework. The tree now has a few more acks from
>> > people, and it's largely in the same situation as HSI is: I'll
>> > probably pull, but I really wanted the users who are impacted to
>> > actually talk to me about it.
>> >
>> Hi,
>>
>> Now Marek and Nvidia persons are used it for DMA mapping based IOMMU.
>>
>> Are there other person who help to merge it?
>> (+CC related persons).
>
> I can give a little more background information.
>
> We used to have separate implementations of dma_map_ops for each
> architecture that had the need to abstract dma_alloc_coherent
> and dma_map_* across both IOMMU and linear (virt_to_bus style)
> mappings and/or swiotlb. Those dma_map_ops imlpementations were
> already merged before the start of the git history and subsequently
> got used on powerpc, ia64, x86_64, sparc, alpha, mips, unicore32
> and hexagon, roughly in that order.
>
> We are seeing lots of IOMMUs come up on ARM now, but unfortunately
> the existing dma_map_ops do not cover the need on ARM to have
> two different kind of coherent memory (write-combine and not
> write-combine) that we have traditionally abstracted using
> the dma_alloc_coherent and dma_alloc_writecombine functions on both
> arm and avr32. In order to support IOMMUs on ARM using the same
> API as everyone else, I've asked Marek to use dma_map_ops on
> ARM, which requires slightly extending the include/linux/dma-mapping.h
> interfaces so they cover this variation.
>
> The actually interesting work to implement a better abstraction for
> IOMMUs, building the dma-mapping.h API on top of the iommu.h API
> in an architecture independent way has also been implemented but
> requires these changes as a prerequisite.
>
>        Arnd

Out of curiosity where is the IOMMU abstraction work being discussed ?
Worked on ? I would like similar things on x86 platform and i spend
sometimes thinking on it in the past. Would like to make sure this
could also fit our need.

Cheers,
Jerome