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

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Date:   Thu, 27 Oct 2022 15:55:50 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Elliot Berman <quic_eberman@...cinc.com>,
        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

On 27/10/2022 12:17, Elliot Berman wrote:
> 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.

You still did not answer from where does 1.0 come from... Compatibles
are usually expected to be specific.

Best regards,
Krzysztof