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

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Date:   Tue, 31 May 2022 20:09:19 +0300
From:   Oleksandr <olekstysh@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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 31.05.22 14:52, Krzysztof Kozlowski wrote:

Hello Krzysztof

> 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".


ok, will change


>
>> +        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.


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