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

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Message-ID: <ca13eb92-9b5b-19fd-27a5-f91f5048b142@quicinc.com>
Date:   Thu, 13 Oct 2022 16:58:53 -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


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.

We do similar for firmware in the qcom,scm bindings and following that 
principle.

>> +
>> +  "#address-cells":
>> +    description: Number of cells needed to represent 64-bit capability IDs.
>> +    const: 2
>> +
>> +  "#size-cells":
>> +    description: must be 0, because capability IDs are not memory address
>> +                  ranges and do not have a size.
>> +    const: 0
>> +
>> +patternProperties:
>> +  "^gunyah-resource-mgr(@.*)?":
>> +    type: object
>> +    description:
>> +      Resource Manager node which is required to communicate to Resource
>> +      Manager VM using Gunyah Message Queues.
>> +
>> +    properties:
>> +      compatible:
>> +        items:
>> +          - const: gunyah-resource-manager-1-0
>> +          - const: gunyah-resource-manager
> 
> Same comment here.
> 
>> +
>> +      reg:
>> +        items:
>> +          - description: Gunyah capability ID of the TX message queue
>> +          - description: Gunyah capability ID of the RX message queue
>> +
>> +      interrupts:
>> +        items:
>> +          - description: Interrupt for the TX message queue
>> +          - description: Interrupt for the RX message queue
>> +
>> +    additionalProperties: false
>> +
>> +    required:
>> +      - compatible
>> +      - reg
>> +      - interrupts
>> +
>> +additionalProperties: false
>> +
>> +required:
>> +  - compatible
>> +  - "#address-cells"
>> +  - "#size-cells"
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
>> +
>> +    hypervisor {
>> +        #address-cells = <2>;
>> +        #size-cells = <0>;
>> +        compatible = "gunyah-hypervisor-1.0", "gunyah-hypervisor";
>> +
>> +        gunyah-resource-mgr@0 {
>> +            compatible = "gunyah-resource-manager-1-0", "gunyah-resource-manager";
>> +            interrupts = <GIC_SPI 3 IRQ_TYPE_EDGE_RISING>, /* TX full IRQ */
>> +                         <GIC_SPI 4 IRQ_TYPE_EDGE_RISING>; /* RX empty IRQ */
>> +            reg = <0x00000000 0x00000000>, <0x00000000 0x00000001>;
>> +                  /* TX, RX cap ids */
>> +        };
>> +    };
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 91d00b00d91c..ef6de7599d98 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -8884,6 +8884,7 @@ M:	Elliot Berman <quic_eberman@...cinc.com>
>>   M:	Murali Nalajala <quic_mnalajal@...cinc.com>
>>   L:	linux-arm-msm@...r.kernel.org
>>   S:	Supported
>> +F:	Documentation/devicetree/bindings/firmware/gunyah-hypervisor.yaml
>>   F:	Documentation/virt/gunyah/
>>   
>>   HABANALABS PCI DRIVER
>> -- 
>> 2.25.1
>>
>>