Re: [PATCH] xen/evtchn: Add design for static event channel signaling for domUs..

[Julien Grall <julien@xxxxxxx>]

Hi Stefano,

On 12/04/2022 21:39, Stefano Stabellini wrote:
> > > I should mention that it would be also possible to use sub-nodes to
> > > express this information:
> > >
> > > 2)
> > >           domU1: domU1 {
> > >               ...
> > >               /* one sub-node per local event channel */
> > >               ec1: evtchn@a {
> > >                   compatible = "xen,evtchn-v1";
> > >                   /* local-evtchn link-to-foreign-evtchn */
> > >                   xen,evtchn = <0xa &ec3>
> > >               };
> > >               ec2: evtchn@c {
> > >                   compatible = "xen,evtchn-v1";
> > >                   xen,evtchn = <0xc &ec4>
> > >               };
> > >           };
> > >
> > >           domU2: domU2 {
> > >               ...
> > >               ec3: evtchn@b {
> > >                   compatible = "xen,evtchn-v1";
> > >                   xen,evtchn = <0xb &ec1>
> > >               };
> > >               ec4: evtchn@d {
> > >                   compatible = "xen,evtchn-v1";
> > >                   xen,evtchn = <0xd &ec2>
> > >               };
> > >           };
> > >       };
> > As for 1), you could combine all the ports in one node.
> I thought about it but I couldn't come up with a way to do that which
> retains the simplicity of this example. The problem is that in device
> tree you can only link to nodes, not to individual properties. So I
> think we would have to have separate nodes for each event channel so
> that we could separately link to them.
Ah yes. I overlooked it when making the suggestion. That said, I think 
my point in my previous e-mail stands.
If this is too verbose, then we could provide macro to generate the 
event channel node.
> Otherwise, we would have to add the foreign event channel number in
> addition to the link to be able to distinguish them. And that would
> result in duplicated information. E.g.:
This is not indeed not great.

>         domU1: domU1 {
>             ...
>             /* one sub-node per local event channel */
>             ec1: evtchn@a {
>                 compatible = "xen,evtchn-v1";
>                 /* local-evtchn link-to-foreign foreign-evtchn */
>                 xen,evtchn = <0xa &ec2 0xa 0xc &ec2 0xd>
>             };
>         };
>
>         domU2: domU2 {
>             ...
>             ec2: evtchn@b {
>                 compatible = "xen,evtchn-v1";
>                 xen,evtchn = <0xb &ec1 0xa 0xd &ec1 0xc>
>             };
>         };
Cheers,

--
Julien Grall