Re: [Qemu-devel] [PATCH] virtio-pci: Fix endianness of virtio config

[Alexander Graf]

On 10.01.2012, at 22:04, Benjamin Herrenschmidt wrote:

> On Tue, 2012-01-10 at 21:46 +0100, Alexander Graf wrote:
>> On 10.01.2012, at 21:35, Andreas Färber wrote:
>> 
>>> Am 10.01.2012 21:30, schrieb Alexander Graf:
>>>> Maybe the RTAS callbacks really want you to return stuff in little
>> endian?
>>> 
>>> IIRC all RTAS callbacks need to be in the same bitness and
>> endianness
>>> (MSR LE+SB) as when instantiating RTAS from OF.
>> 
>> Sure, the question is how the PCI controller is wired up usually. Just
>> because RTAS works in native endianness doesn't mean that endianness
>> of the actual device access isn't defined differently.
> 
> Eugh... you guys don't get it :-) This is -not- about the PCI
> configuration space, but the virtio configuration space which is a
> slightly different thing (PCI config space works with what's there at
> the moment).
> 
> So this has nothing to do with e1000 or any other emulated device like
> that, but it does have to do with virtio-blk for example.

Ah, yeah, sorry, didn't get that part :).

> The way virtio works is that the PIO BAR is split into two parts. The
> first part (header) is a set of what's basically pseudo MMIO registers
> that are little endian. The second part is device-specific an is ...
> guest native endian. (Yeah it's horrible, I know).
> 
> This is how it's specified in the virtio spec and how Linux expects it,
> with this patch, I can boot an existing fedora 16 with virtio-blk for
> example.

Here's the thing that I don't understand. What exactly is breaking for you? I 
tried -M pseries on a ppc box and on an x86 box and both times was able to see 
/dev/vda.


Alex