Re: [PATCH 14/16] hw/i3c: remote_i3c: Add model

[Joe Komlodi <komlodi@google.com>]

Hi Jeremy,

On Sun, Apr 2, 2023 at 11:14 PM Jeremy Kerr <jk@codeconstruct.com.au> wrote:
>
> Hi Joe,
>
> > Adds a model to communicate to remote I3C devices over chardev. This
> > allows QEMU to communicate to I3C targets that exist outside of QEMU.
>
> Nice!
>
> I've been wanting something similar for a while, both for i2c and i3c
> busses, to the point of having a similar concept partly implemented.
>
> A couple of design decisions though:
>
> 1) Is this something that qemu upstream would accept? Do we need a
> formal description of the guest-to-host interface somewhere? Or is there
> a more standard way of exposing busses like this?
>
Not sure! I'm open to ideas.
I think the most controversial portion of the remote target like this
might be doing socket transfers in an MMIO context.
i.e. driver does a write to I3C controller -> triggers a transaction
to remote target -> remote target sends/reads data over socket.

Because of that, we might need to add a way to do these transactions
asynchronously.

> 2) My approach was at the bus level rather than the device level: the
> protocol is bidirectional to allow the model to either participate as a
> i3c controller or a target. There's quite a bit of mis-fit when applying
> that to the qemu device structure though, so your approach is a lot
> cleaner.
>
> I'll have a go at adapting my client to your protocol, and see how the
> device interface goes.
>
> Assuming we do adopt your approach though, I think the protocol
> description needs some work. There seems to be other messages not listed
> in your protocol comments, and the direction of some seems to be
> reversed. I'm happy to contribute to that documentation if you like.

Oops. I'll reread and revise in v2. If you have anything else you want
to add too, let me know and I'll add them as well.

Thanks,
Joe

>
> Cheers,
>
>
> Jeremy