On Mon, Jun 08, 2020 at 05:19:06AM -0400, Michael S. Tsirkin wrote:

On Mon, Jun 08, 2020 at 11:11:00AM +0200, Guennadi Liakhovetski wrote:

quoted

Update: I looked through VirtIO 1.0 and 1.1 specs, data format their, 
including byte order, is defined on a per-device type basis. RPMsg is 
indeed included in the spec as device type 7, but that's the only 
mention of it in both versions. It seems RPMsg over VirtIO isn't 
standardised yet.

Yes. And it would be very good to have some standartization before we
keep adding things. For example without any spec if host code breaks
with some guests, how do we know which side should be fixed?

quoted

Also it looks like newer interface definitions 
specify using "guest native endianness" for Virtual Queue data.

They really don't or shouldn't. That's limited to legacy chapters.
Some definitions could have slipped through but it's not
the norm. I just quickly looked through the 1.1 spec and could
not find any instances that specify "guest native endianness"
but feel free to point them out to me.

Oh, there you go. No, sorry, my fault, it's the other way round: "guest 
native" is for legacy and LE is for current / v1.0 and up.

quoted

So 
I think the same should be done for RPMsg instead of enforcing LE?

That makes hardware implementations as well as any cross-endian
hypervisors tricky.

Yes, LE it is then. And we need to add some text to the spec.

In theory there could be a backward compatibility issue - in case someone 
was already using virtio_rpmsg_bus.c in BE mode, but I very much doubt 
that...

Thanks
Guennadi