Re: [PATCH v5 02/13] dt-bindings: Add binding for gunyah hypervisor

[Elliot Berman]

Hi Rob,

On 10/26/2022 2:16 PM, Rob Herring wrote:
> On Thu, Oct 13, 2022 at 6:59 PM Elliot Berman <quic_eberman@xxxxxxxxxxx> wrote:
> > On 10/12/2022 8:56 AM, Rob Herring wrote:
> > > On Mon, Oct 10, 2022 at 05:08:29PM -0700, Elliot Berman wrote:
> > > > When Linux is booted as a guest under the Gunyah hypervisor, the Gunyah
> > > > Resource Manager applies a devicetree overlay describing the virtual
> > > > platform configuration of the guest VM, such as the message queue
> > > > capability IDs for communicating with the Resource Manager. This
> > > > information is not otherwise discoverable by a VM: the Gunyah hypervisor
> > > > core does not provide a direct interface to discover capability IDs nor
> > > > a way to communicate with RM without having already known the
> > > > corresponding message queue capability ID. Add the DT bindings that
> > > > Gunyah adheres for the hypervisor node and message queues.
> > > >
> > > > Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx>
> > > > ---
> > > >    .../bindings/firmware/gunyah-hypervisor.yaml  | 87 +++++++++++++++++++
> > > >    MAINTAINERS                                   |  1 +
> > > >    2 files changed, 88 insertions(+)
> > > >    create mode 100644 Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml b/Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
> > > > new file mode 100644
> > > > index 000000000000..f0a14101e2fd
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
> > > > @@ -0,0 +1,87 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/firmware/gunyah-hypervisor.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: Gunyah Hypervisor
> > > > +
> > > > +maintainers:
> > > > +  - Murali Nalajala <quic_mnalajal@xxxxxxxxxxx>
> > > > +  - Elliot Berman <quic_eberman@xxxxxxxxxxx>
> > > > +
> > > > +description: |+
> > > > +  On systems which support devicetree, Gunyah generates and overlays a deviceetree overlay which
> > >
> > > How you end up with the node (applying an overlay) is not relavent to
> > > the binding.
> > >
> > > > +  describes the basic configuration of the hypervisor. Virtual machines use this information to determine
> > > > +  the capability IDs of the message queues used to communicate with the Gunyah Resource Manager.
> > >
> > > Wrap at 80. That is the coding standard still though 100 is deemed
> > > allowed. And yamllint only complains at 110 because I didn't care to fix
> > > everyones lines over 100.
> > >
> > > > +  See also: https://github.com/quic/gunyah-resource-manager/blob/develop/src/vm_creation/dto_construct.c
> > > > +
> > > > +properties:
> > > > +  compatible:
> > > > +    items:
> > > > +      - const: gunyah-hypervisor-1.0
> > > > +      - const: gunyah-hypervisor
> > >
> > > 2 compatibles implies a difference between the 2. What's the difference?
> > > Where does '1.0' come from?
> >
> > There's no difference. I thought the convention was to have
> > device-specific compatible and the generic compatible. "device-specific"
> > here would be specific to version of Gunyah since it's software.
>
> No, that's just what people do because "vendor,new-soc",
> "vendor,old-soc" seems to bother them for some reason. At the end of
> the day, it's just a string identifier that means something. If
> there's no difference in that 'something', then there is no point in
> having more than one string.
>
> You only need something specific enough to discover the rest from the
> firmware. When that changes, then you add a new compatible. Of course,
> if you want existing OSs to work, then better not change the
> compatible.

Thanks for the info, I'll drop the "-1.0" suffix.