linux-kernel - Re: [PATCH V2 5/7] dt-bindings: Add xen,dev-domid property description for xen-grant DMA ops

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Message-ID: <CAK8P3a2cAnXr8TDDYTiFxTWzQxa67sGnYDQRRD+=Q8_cSb1mEw@mail.gmail.com>
Date:   Wed, 18 May 2022 15:32:27 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Oleksandr Tyshchenko <olekstysh@...il.com>
Cc:     xen-devel <xen-devel@...ts.xenproject.org>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@...ts.linux-foundation.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Jason Wang <jasowang@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.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>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH V2 5/7] dt-bindings: Add xen,dev-domid property
 description for xen-grant DMA ops

On Sat, May 7, 2022 at 7:19 PM Oleksandr Tyshchenko <olekstysh@...il.com> wrote:
>
> 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
> +
>  required:
>    - compatible
>    - reg

Sorry for joining the discussion late. Have you considered using the
generic iommu
binding here instead of a custom property? This would mean having a device
node for the grant-table mechanism that can be referred to using the 'iommus'
phandle property, with the domid as an additional argument.

It does not quite fit the model that Linux currently uses for iommus,
as that has an allocator for dma_addr_t space, but it would think it's
conceptually close enough that it makes sense for the binding.

         Arnd