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SubjectRe: [PATCH V3 5/8] dt-bindings: Add xen,grant-dma IOMMU description for xen-grant DMA ops
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On 01.06.22 03:34, Stefano Stabellini wrote:

Hello Stefano

> On Tue, 31 May 2022, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> 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@epam.com>
>> ---
>> 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@kernel.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.
> 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@kernel.org>

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
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel@lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
--
Regards,

Oleksandr Tyshchenko

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