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

[andrzej zaborowski]

On 06/04/2008, Anthony Liguori <address@hidden> wrote:
> Blue Swirl wrote:
> >  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.

As a note, the DMA controllers in the ARM system-on-chip's can
byte-swap, do 90deg rotation of 2D arrays, transparency (probably
intened for image blitting, but still available on any kind of
transfers), etc., and most importantly issue interrupts on reaching
different points of a transfer.  It is not worth worrying about them
in this API.  I have been for some time wanting to make a separate api
called soc_dma whose task would be using simply memcpy (or zero-copy)
in the most basic case (interrupts off, no transparency,
same-endianness endpoints), as these properties are common for DMA on
the TI OMAPs, the Intel PXAs and the Samsung S3Cs (which otherwise
have little in common).

Cheers
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