On Tue, Aug 12, 2025 at 4:50 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> Hi Rob,
>
> On 30-07-25, 08:39, Rob Herring wrote:
> > On Wed, Jul 30, 2025 at 4:29 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
> > > ### Memory Mapping and Reserved Memory Usage
> > >
> > > The first two patches enhance the reserved-memory subsystem to support attaching
> > > struct device`s that do not originate from DT nodes — essential for virtual or
> > > dynamically discovered devices like the FF-A or loopback buses.
> >
> > We support creating devices from reserved-memory nodes.
>
> I didn't know about this.
>
> > Just add a
> > compatible which you should do anyways because node names are not
> > supposed to be that specific or an ABI.
>
> Yeah, I already knew that the node-names thing isn't going to fly as
> you and Krzysztof rightly pointed out. I just wanted inputs from you
> guys and so did that as a first implementation to get the discussion
> started.
>
> I tried something like this now:
>
> reserved-memory {
> #address-cells = <2>;
> #size-cells = <2>;
> ranges;
>
> rmem@100000000 {
> compatible = "restricted-dma-pool", "virtio-msg,loopback";
The order is wrong here. The 2nd one seems more specific to me. But is
"restricted-dma-pool" useful? Should an OS that only understands that
and not "virtio-msg,loopback" use it?
The format of compatibles is <vendor>,<device/block/interface> and
"virtio-msg" is not a vendor.
> reg = <0x00000001 0x00000000 0x0 0x00400000>; /* 4 MiB */
> };
> };
>
> and this works fine. I am adding two compatibles for virtio-msg:
> "virtio-msg,loopback" and "virtio-msg,ffa". Yes I will properly
> document them in the next version.
Why do you need 2 compatibles? Can't you discover what the remote end
is with some message? We only define "virtio-mmio" in DT for example,
not that the device is a console, rng, etc.
Rob
