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

[Oleksandr]

On 31.05.22 14:52, Krzysztof Kozlowski wrote:

Hello Krzysztof

> On 30/05/2022 23:00, Oleksandr Tyshchenko wrote:
> > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> 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@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.
> > +
> > +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".


ok, will change


> > +        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>;
> 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.


I got it.  There is nothing specific from the device tree's perspective, 
I was thinking to draw attention to the IOMMU specifier (in our case, 
the master device's ID == backend's domain ID). But  '#iommu-cells' 
description above already clarifies that. Will drop.


> > +    };
>
> Best regards,
> Krzysztof

--
Regards,

Oleksandr Tyshchenko