[Sound-open-firmware] [PATCH v3 0/5] Add a vhost RPMsg API

[Guennadi Liakhovetski]

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:
> > 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?
> 
> > 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.

> > 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