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

[Oleksandr <olekstysh@xxxxxxxxx>]

On 01.06.22 03:34, Stefano Stabellini wrote:

Hello Stefano

> On Tue, 31 May 2022, Oleksandr Tyshchenko wrote:
> > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> >
> > The main purpose of this binding is to communicate Xen specific
> > information using generic IOMMU device tree bindings (which is
> > a good fit here) rather than introducing a custom property.
> >
> > Introduce Xen specific IOMMU for the virtualized device (e.g. virtio)
> > to be used by Xen grant DMA-mapping layer in the subsequent commit.
> >
> > 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 domid (domain ID) is used as an argument to the Xen 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@xxxxxxxx>
> > ---
> > 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
> >
> > Change V2 -> V3:
> >     - Stefano already gave his Reviewed-by, I dropped it due to the changes 
> > (significant)
> >     - use generic IOMMU device tree bindings instead of custom property
> >       "xen,dev-domid"
> >     - change commit subject and description, was
> >       "dt-bindings: Add xen,dev-domid property description for xen-grant DMA 
> > ops"
> > ---
> >   .../devicetree/bindings/iommu/xen,grant-dma.yaml   | 49 ++++++++++++++++++++++
> >   1 file changed, 49 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/iommu/xen,grant-dma.yaml
> >
> > 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@xxxxxxxxxx>
> > +
> > +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.
> I think this is OK and in line with the discussion we had on the list. I
> propose the following wording instead:
>
> """
> The Xen IOMMU represents the Xen grant table interface. Grant mappings
> are to be used with devices connected to the Xen IOMMU using the
> "iommus" property, which also specifies the ID of the backend domain.
> 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.
> Here I would say:
>
> """
> The single cell is the domid (domain ID) of the domain where the backend
> is running.
> """
>
> With the two wording improvements:
I am happy with proposed wording improvements, will update.


> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Thanks!


> > +required:
> > +  - compatible
> > +  - "#iommu-cells"
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    xen_iommu {
> > +        compatible = "xen,grant-dma";
> > +        #iommu-cells = <1>;
> > +    };
> > +
> > +    virtio@3000 {
> > +        compatible = "virtio,mmio";
> > +        reg = <0x3000 0x100>;
> > +        interrupts = <41>;
> > +
> > +        /* The backend is located in Xen domain with ID 1 */
> > +        iommus = <&xen_iommu 1>;
> > +    };
> > --
> > 2.7.4
> >
> >
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> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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--
Regards,

Oleksandr Tyshchenko