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From: Rusty Russell <rusty@rustcorp.com.au>
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Date: Fri, 21 Feb 2014 09:56:46 +1030
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Subject: Re: [Qemu-devel] [PATCH 1/8] virtio_get_byteswap: function for
	endian-ambivalent targets using virtio.
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To: Alexander Graf <agraf@suse.de>, Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>, "peter.maydell@linaro.org" <peter.maydell@linaro.org>, "thuth@linux.vnet.ibm.com" <thuth@linux.vnet.ibm.com>, "Michael S. Tsirkin" <mst@redhat.com>, "marc.zyngier@arm.com" <marc.zyngier@arm.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "stefanha@redhat.com" <stefanha@redhat.com>, "anthony@codemonkey.ws" <anthony@codemonkey.ws>, "pbonzini@redhat.com" <pbonzini@redhat.com>, "afaerber@suse.de" <afaerber@suse.de>, Greg Kurz <gkurz@linux.vnet.ibm.com>

Alexander Graf <agraf@suse.de> writes:
> On 02/18/2014 05:17 PM, Cornelia Huck wrote:
>> Hm. So whatever_le for 1.0 devices, and virtio_whatever (checking the
>> byteswap value) for legacy devices? The device implementation will be
>> aware of the virtio version anyway.
>
> Yeah, but I would hope we want to share as much code as possible here, 
> so that config accessors can be shared between legacy virtio and 1.0 
> virtio. And in that case we want to have a generic helper to read/write 
> pieces of that config space - which this patch introduces for us :).
>
>> (Btw., can some of those architectures supporting both le/be run with
>> mixed le/be cpus? That would be a mess for legacy devices.)
>
> Yes, they can. No, we don't care :).

There's per-cpu (what endian) and per-device (legacy or no).  To do this
Right, we'd need to consult both, but we don't always have that
information.  So this the minimal viable solution.

We'll need a per-device legacy flag eventually (there are other changes
than just endian).  But getting the wrappers in place is a good first
step.

Cheers,
Rusty.