Re: [kvm-devel] [Qemu-devel] [PATCH 2/6] PCI DMA API (v2)

[Anthony Liguori <anthony@codemonkey.ws>]

Blue Swirl wrote:
> On 4/5/08, Anthony Liguori <aliguori@us.ibm.com> wrote:
>   
>> This patch introduces a PCI DMA API and some generic code to support other DMA
>>  APIs.  It introduces a IOVector type that contains physical address/length
>>  pairs.  These vectors can be translated by the PCI layer and passed either to
>>  generic copying functions or directly to the block or network subsystems.
>>     
>
> But cpu_map_physical_page can't be the correct function for
> translation for every case.

cpu_map_physical_page is the last function you call after you have 
already translated the IOVector however many times you need to.  It's 
only used within the IO infrastructure (net, block) which are passed 
fully translated IOVectors.

>  To support Sparc IOMMU and DMA controller
> I need a way to call a series of different translation functions
> depending on the bus where we are. For the byte swapping case the
> memcpy functions must be dynamic as well.
>   

Does DMA really byte-swap?  I know PCI controllers byte swap within the 
configuration space but I didn't think they byte-swapped DMA transfers.  
I'm not even sure how that would work.

Regards,

Anthony Liguori

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