Re: [Qemu-devel] [PATCH] virtio-pci: implement cfg capability

[Michael S. Tsirkin]

On Mon, Jul 06, 2015 at 10:11:18AM +0100, Peter Maydell wrote:
> On 6 July 2015 at 10:06, Michael S. Tsirkin <address@hidden> wrote:
> > On Mon, Jul 06, 2015 at 10:46:31AM +0200, Paolo Bonzini wrote:
> >> Why host endian and not device (in this case little) endian?
> 
> > It's the endian of the originator of the transaction.
> > And emulated device code is all compiled in host endian-ness.
> 
> But address_space_rw() is just the "memcpy bytes to the
> target's memory" operation -- if you have a pile of bytes
> then there are no endianness concerns. If you don't have
> a pile of bytes then you need to know the structure of
> the data you're DMAing around, and you should probably
> have a loop doing things with the specify-the-width functions.
> 
> thanks
> -- PMM

Absolutely. But what if DMA happens to target another device
and not memory? Device needs some endian-ness so it needs
to be converted to that.

-- 
MST