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

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Date:   Thu, 27 Oct 2022 09:17:13 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Rob Herring <robh@...nel.org>
CC:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        "Srivatsa Vaddagiri" <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 02/13] dt-bindings: Add binding for gunyah hypervisor

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@...cinc.com> 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@...cinc.com>
>>>> ---
>>>>    .../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@...cinc.com>
>>>> +  - Elliot Berman <quic_eberman@...cinc.com>
>>>> +
>>>> +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.