linux-kernel - Re: [PATCH V3 5/8] dt-bindings: Add xen,grant-dma IOMMU description for xen-grant DMA ops

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Message-ID: <15eef004-74c7-0eb5-3f87-86e164ef70ff@linaro.org>
Date:   Tue, 31 May 2022 13:52:14 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Oleksandr Tyshchenko <olekstysh@...il.com>,
        xen-devel@...ts.xenproject.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org
Cc:     Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Rob Herring <robh+dt@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Julien Grall <julien@....org>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH V3 5/8] dt-bindings: Add xen,grant-dma IOMMU description
 for xen-grant DMA ops

On 30/05/2022 23:00, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>

Thank you for your patch. There is something to discuss/improve.

> diff --git a/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml b/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
> new file mode 100644
> index 00000000..ab5765c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
> @@ -0,0 +1,49 @@
> +# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iommu/xen,grant-dma.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Xen specific IOMMU for virtualized devices (e.g. virtio)
> +
> +maintainers:
> +  - Stefano Stabellini <sstabellini@...nel.org>
> +
> +description:
> +  The reference to Xen specific IOMMU node using "iommus" property indicates
> +  that Xen grant mappings need to be enabled for the device, and it specifies
> +  the ID of the domain where the corresponding backend resides.
> +  The binding is required to restrict memory access using Xen grant mappings.
> +
> +properties:
> +  compatible:
> +    const: xen,grant-dma
> +
> +  '#iommu-cells':
> +    const: 1
> +    description:
> +      Xen specific IOMMU is multiple-master IOMMU device.
> +      The single cell describes the domid (domain ID) of the domain where
> +      the backend is running.
> +
> +required:
> +  - compatible
> +  - "#iommu-cells"
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    xen_iommu {

No underscores in node names, generic node names, so this looks like
"iommu".

> +        compatible = "xen,grant-dma";
> +        #iommu-cells = <1>;
> +    };
> +
> +    virtio@...0 {
> +        compatible = "virtio,mmio";
> +        reg = <0x3000 0x100>;
> +        interrupts = <41>;
> +
> +        /* The backend is located in Xen domain with ID 1 */
> +        iommus = <&xen_iommu 1>;

There is no need usually to give consumer examples in provider binding.
If there is nothing specific here (looks exactly like every IOMMU
consumer in Linux kernel), drop the consumer.

> +    };


Best regards,
Krzysztof