Re: [Qemu-devel] [PATCH v3 3/4] target-ppc: ppc can be either endian

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

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.

> ?
> 
> (Will Deacon just suggested this as a possibility on the
> kvm-arm mailing list...)
> 

Just discovered some virtio endian threads in the kvm-arm@ archives...
I'll take some time to read.

> Also, are we documenting what the process should be for a
> virtio implementation to decide the endianness for a particular
> architecture? I assume we'd like kvmtool and QEMU to do
> the same thing rather than subtly different things...
> 

Sure !

> thanks
> -- PMM
> 

Thanks.

-- 
Gregory Kurz                                     kurzgreg@fr.ibm.com
                                                 gkurz@linux.vnet.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)562 165 496

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.