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

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH] virtio-pci: implement cfg capability
Date: Mon, 6 Jul 2015 13:31:56 +0300

On Mon, Jul 06, 2015 at 11:04:24AM +0100, Peter Maydell wrote:
> On 6 July 2015 at 11:03, Michael S. Tsirkin <address@hidden> wrote:
> > On Mon, Jul 06, 2015 at 10:11:18AM +0100, Peter Maydell wrote:
> >> 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.
> > 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.
> Yes, and address_space_rw() already deals with conversion to
> that device's specified endianness.
> -- PMM

Yes, but incorrectly if target endian != host endian.
For example, LE target and LE device on BE host.

IO callbacks always get a native endian format so they expect to get
byte 0 of the buffer in MSB on this host.


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