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Date: Wed, 07 May 2014 11:09:56 +0200
From: Alexander Graf <agraf@suse.de>
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Subject: Re: [Qemu-devel] [PATCH v3 3/4] target-ppc: ppc can be either endian
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To: Greg Kurz <gkurz@linux.vnet.ibm.com>, Peter Maydell <peter.maydell@linaro.org>
Cc: bharata@linux.vnet.ibm.com, "qemu-ppc@nongnu.org" <qemu-ppc@nongnu.org>, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>, QEMU Developers <qemu-devel@nongnu.org>


On 07.05.14 10:14, Greg Kurz wrote:
> On Tue, 6 May 2014 19:37:22 +0100
> Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 5 May 2014 09:07, Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:
>>> POWER7, POWER7+ and POWER8 families use the ILE bit of the LPCR
>>> special purpose register to decide the endianness to use when
>>> entering interrupt handlers. When running a Linux guest, this
>>> provides a hint on the endianness used by the kernel. From a
>>> QEMU point of view, the information is needed for legacy virtio
>>> support and crash dump support as well.
>> Do you care about the case of:
>>   * kernel bigendian
> Yes. FWIW, ppc64 is still widely used in big endian mode we don't
> want to break.
>
>>   * userspace littleendian (or vice-versa)
> We don't care about userspace here. We assume that virtio structures are
> owned by the guest kernel.
>
>>   * guest kernel passes virtio device through to guest userspace
> Not sure to understand... could you please point me to an example ?
>
>>   * guest userspace is doing the manipulation of the device
>>
> Hmm... you mean we would have virtio drivers implemented in the guest
> userspace ? Does that exist ? Please elaborate.

Virtio bypasses the IOMMU by design, so user space drivers don't make 
sense here :).

I don't think we should overengineer hacks for legacy virtio.


Alex