linux-kernel - Re: [PATCH v2 2/2] dt-bindings: xen: Add xen,scmi-devid property description for SCMI

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Date:   Mon, 7 Mar 2022 15:38:12 -0800 (PST)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>
cc:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Cristian Marussi <cristian.marussi@....com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] dt-bindings: xen: Add xen,scmi-devid property
 description for SCMI

On Mon, 7 Mar 2022, Oleksii Moisieiev wrote:
> Document xen,scmi-devid property for the devices, using SCMI protocol
> to work with clocks/resets/power-domains etc. This property is intended
> to set the device_id, which should be used to manage device permissions
> in the Firmware. Device permissions management described in DEN 0056,
> Section 4.2.2.10 [0].
> 
> This property is used by Xen hypervisor, which works as trusted Agent, to
> set permissions for the devices, passed-through to the Guest Domains,
> which are non-trusted Agents. Trusted and non-trusted Agent terms described
> in Section 4.1.1 [0].
> 
> [0] https://developer.arm.com/documentation/den0056/latest

Aside from minor grammar improvements (see below), I don't have any
feedback. This is OK from my point of view.


> Signed-off-by: Oleksii Moisieiev <oleksii_moisieiev@...m.com>
> ---
>  .../bindings/firmware/xen,scmi-devid.yaml     | 42 +++++++++++++++++++
>  1 file changed, 42 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/firmware/xen,scmi-devid.yaml
> 
> diff --git a/Documentation/devicetree/bindings/firmware/xen,scmi-devid.yaml b/Documentation/devicetree/bindings/firmware/xen,scmi-devid.yaml
> new file mode 100644
> index 000000000000..49dc9951b54d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/xen,scmi-devid.yaml
> @@ -0,0 +1,42 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +# Copyright 2022 EPAM Systems.
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/firmware/xen,scmi-devid.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Xen SCMI (System Control and Management Interface) Device ID binding
> +
> +maintainers:
> +  - Oleksii Moisieiev <oleksii_moisieiev@...m.com>
> +
> +select: true
> +
> +description: |
> +  SCMI device_id property is intended to set the device id, needed to manage
> +  the device permissions via SCMI protocol in the firmware. The device_id
> +  should match device ids, defined in the firmware so the device permissions
> +  can be requested by sending BASE_SET_DEVICE_PERMISSIONS (see 4.2.2.10 of [0]).

I would say:

The xen,scmi-devid property is the SCMI device id, which is needed to
manage device permissions with the SCMI protocol. The xen,scmi-devid
property should match device ids as defined in firmware, so that device
permissions can be requested with BASE_SET_DEVICE_PERMISSIONS (see
4.2.2.10 of [0]).


> +  This property is used by Xen hypervisor to set the device permissions for
> +  the Guest Domains. Where Xen is trusted Agent and Guest Domains are
> +  non-trusted Agents.

I would say:

This property is used by a Trusted Agent, e.g. the Xen hypervisor, to
set device permissions for non-trusted Agents, e.g. Xen domains.


> +  [0] https://developer.arm.com/documentation/den0056/latest
> +
> +properties:
> +  xen,scmi-devid:
> +    description: Identifier of the device, matching device id, defined in
> +      the firmware.

description: Identifier of the device, matching the SCMI device id as
defined in firmware


> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
> +additionalProperties: true
> +
> +examples:
> +  - |
> +    ohci1: usb@...a0000 {
> +        /* ... */
> +        reg = <0xee0a0000 0x100>;
> +        xen,scmi-devid = <11>;
> +        clocks = <&scmi_clock 4>;
> +    };
> -- 
> 2.27.0
>