Date:   Mon, 31 Oct 2022 20:19:45 -0700
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 10/27/2022 12:55 PM, Krzysztof Kozlowski wrote:
> 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.
> 

The 1.0 comes from the Gunyah version. This is the same version returned 
by "hyp_identify" hypercall.

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