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Date:   Mon, 16 May 2022 19:27:50 -0500
From:   Rob Herring <robh@kernel.org>
To:     Oleksandr Tyshchenko <olekstysh@gmail.com>
Cc:     xen-devel@lists.xenproject.org,
        virtualization@lists.linux-foundation.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Jason Wang <jasowang@redhat.com>,
        Krzysztof Kozlowski <krzk+dt@kernel.org>,
        Julien Grall <julien@xen.org>, Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>
Subject: Re: [PATCH V2 5/7] dt-bindings: Add xen,dev-domid property
 description for xen-grant DMA ops
Message-ID: <20220517002750.GA3638680-robh@kernel.org>
References: <1651947548-4055-1-git-send-email-olekstysh@gmail.com>
 <1651947548-4055-6-git-send-email-olekstysh@gmail.com>
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On Sat, May 07, 2022 at 09:19:06PM +0300, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> Introduce Xen specific binding for the virtualized device (e.g. virtio)
> to be used by Xen grant DMA-mapping layer in the subsequent commit.
> 
> This binding indicates that Xen grant mappings scheme needs to be
> enabled for the device which DT node contains that property and specifies
> the ID of Xen domain where the corresponding backend resides. The ID
> (domid) is used as an argument to the grant mapping APIs.
> 
> This is needed for the option to restrict memory access using Xen grant
> mappings to work which primary goal is to enable using virtio devices
> in Xen guests.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> ---
> Changes RFC -> V1:
>    - update commit subject/description and text in description
>    - move to devicetree/bindings/arm/
> 
> Changes V1 -> V2:
>    - update text in description
>    - change the maintainer of the binding
>    - fix validation issue
>    - reference xen,dev-domid.yaml schema from virtio/mmio.yaml
> ---
>  .../devicetree/bindings/arm/xen,dev-domid.yaml     | 37 ++++++++++++++++++++++
>  Documentation/devicetree/bindings/virtio/mmio.yaml |  7 ++++
>  2 files changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> 
> diff --git a/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> new file mode 100644
> index 00000000..750e89e
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> @@ -0,0 +1,37 @@
> +# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/xen,dev-domid.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Xen specific binding for virtualized devices (e.g. virtio)
> +
> +maintainers:
> +  - Stefano Stabellini <sstabellini@kernel.org>
> +
> +select: true

Omit. No need to apply this on every single node.

> +
> +description:
> +  This binding indicates that Xen grant mappings need to be enabled for
> +  the device, and it specifies the ID of the domain where the corresponding
> +  device (backend) resides. The property is required to restrict memory
> +  access using Xen grant mappings.
> +
> +properties:
> +  xen,dev-domid:

I kind of think 'dev' is redundant. Is there another kind of domid 
possible? Maybe xen,backend-domid or just xen,domid? I don't know Xen 
too well, so ultimately up to you all.

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      The domid (domain ID) of the domain where the device (backend) is running.
> +
> +additionalProperties: true
> +
> +examples:
> +  - |
> +    virtio@3000 {
> +            compatible = "virtio,mmio";
> +            reg = <0x3000 0x100>;
> +            interrupts = <41>;
> +
> +            /* The device is located in Xen domain with ID 1 */
> +            xen,dev-domid = <1>;
> +    };
> diff --git a/Documentation/devicetree/bindings/virtio/mmio.yaml b/Documentation/devicetree/bindings/virtio/mmio.yaml
> index 10c22b5..29a0932 100644
> --- a/Documentation/devicetree/bindings/virtio/mmio.yaml
> +++ b/Documentation/devicetree/bindings/virtio/mmio.yaml
> @@ -13,6 +13,9 @@ description:
>    See https://www.oasis-open.org/committees/tc_home.php?wg_abbrev=virtio for
>    more details.
>  
> +allOf:
> +  - $ref: /schemas/arm/xen,dev-domid.yaml#
> +
>  properties:
>    compatible:
>      const: virtio,mmio
> @@ -33,6 +36,10 @@ properties:
>      description: Required for devices making accesses thru an IOMMU.
>      maxItems: 1
>  
> +  xen,dev-domid:
> +    description: Required when Xen grant mappings need to be enabled for device.
> +    $ref: /schemas/types.yaml#/definitions/uint32

No need to define the type again nor describe it again.

Instead, just change additionalProperties to unevaluateProperties in 
this doc. The diff is the latter takes $ref's into account.

> +
>  required:
>    - compatible
>    - reg
> -- 
> 2.7.4
> 
>