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

[Krzysztof Kozlowski]

On 31/10/2022 23:19, Elliot Berman wrote:
> 
> 
> 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@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.
>>
>> 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.

Then dropping 1.0 makes sense - your SW provides auto-detection.

Best regards,
Krzysztof