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Date: Mon, 6 Jul 2015 13:03:27 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] virtio-pci: implement cfg capability
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>, =?iso-8859-1?Q?Herv=E9?= Poussineau <hpoussin@reactos.org>, QEMU Developers <qemu-devel@nongnu.org>

On Mon, Jul 06, 2015 at 10:11:18AM +0100, Peter Maydell wrote:
> On 6 July 2015 at 10:06, Michael S. Tsirkin <mst@redhat.com> 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