Re: [Qemu-devel] [PATCH 1/5] PCI DMA API (v3)

[Anthony Liguori <aliguori@us.ibm.com>]

Blue Swirl wrote:
> On 4/16/08, Anthony Liguori <aliguori@us.ibm.com> wrote:
>   
>> This patch introduces a DMA API and plumbs support through the DMA layer.  We
>>  use a mostly opaque structure, IOVector to represent a scatter/gather list of
>>  physical memory.  Associated with each IOVector is a read/write function and
>>  an opaque pointer.  This allows arbitrary transformation/mapping of the
>>  data while providing an easy mechanism to short-cut the zero-copy case
>>  in the block/net backends.
>>     
>
> This looks much better also for Sparc uses. I converted pcnet to use
> the IOVectors (see patch), it does not work yet but looks doable.
>   

Excellent!

> IMHO the read/write functions should be a property of the bus so that
> they are hidden from the device, for pcnet it does not matter as we
> have to do the swapping anyway.
>   

For an IOMMU that has a per-device mapping, the read/write functions 
have to operate on a per-device basis.

Regards,

Anthony Liguori