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Subject: Re: [PATCH V2 5/7] dt-bindings: Add xen,dev-domid property
 description for xen-grant DMA ops
To:     Rob Herring <robh@kernel.org>, Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>
Cc:     xen-devel@lists.xenproject.org,
        virtualization@lists.linux-foundation.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
        Jason Wang <jasowang@redhat.com>,
        Krzysztof Kozlowski <krzk+dt@kernel.org>,
        Julien Grall <julien@xen.org>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>
References: <1651947548-4055-1-git-send-email-olekstysh@gmail.com>
 <1651947548-4055-6-git-send-email-olekstysh@gmail.com>
 <20220517002750.GA3638680-robh@kernel.org>
From:   Oleksandr <olekstysh@gmail.com>
Message-ID: <fa3be245-ac3c-5637-13a1-3197e78c874d@gmail.com>
Date:   Wed, 18 May 2022 17:12:35 +0300
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On 17.05.22 03:27, Rob Herring wrote:

Hello Rob, all


> On Sat, May 07, 2022 at 09:19:06PM +0300, Oleksandr Tyshchenko wrote:
>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>
>> Introduce Xen specific binding for the virtualized device (e.g. virtio)
>> to be used by Xen grant DMA-mapping layer in the subsequent commit.
>>
>> This binding indicates that Xen grant mappings scheme needs to be
>> enabled for the device which DT node contains that property and specifies
>> the ID of Xen domain where the corresponding backend resides. The ID
>> (domid) is used as an argument to the 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
>> ---
>>   .../devicetree/bindings/arm/xen,dev-domid.yaml     | 37 ++++++++++++++++++++++
>>   Documentation/devicetree/bindings/virtio/mmio.yaml |  7 ++++
>>   2 files changed, 44 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
>> new file mode 100644
>> index 00000000..750e89e
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
>> @@ -0,0 +1,37 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/arm/xen,dev-domid.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Xen specific binding for virtualized devices (e.g. virtio)
>> +
>> +maintainers:
>> +  - Stefano Stabellini <sstabellini@kernel.org>
>> +
>> +select: true
> Omit. No need to apply this on every single node.

ok, will do


>
>> +
>> +description:
>> +  This binding indicates that Xen grant mappings need to be enabled for
>> +  the device, and it specifies the ID of the domain where the corresponding
>> +  device (backend) resides. The property is required to restrict memory
>> +  access using Xen grant mappings.
>> +
>> +properties:
>> +  xen,dev-domid:
> I kind of think 'dev' is redundant. Is there another kind of domid
> possible?


In general, yes. It is driver(frontend) domid. But, at least for now, I 
don't see why we will need an additional property for that.


>   Maybe xen,backend-domid or just xen,domid? I don't know Xen
> too well, so ultimately up to you all.

xen,domid sounds ambiguous to me.

xen,backend-domid sounds perfectly fine to me, I even think it fits better.


Stefano, Juergen, would you be happy with new xen,backend-domid name?

If yes, Stefano could you please clarify, would you be OK if I retained 
your R-b tags (for all patches in current series which touch that 
property) after doing such renaming?


>
>> +    $ref: /schemas/types.yaml#/definitions/uint32
>> +    description:
>> +      The domid (domain ID) of the domain where the device (backend) is running.
>> +
>> +additionalProperties: true
>> +
>> +examples:
>> +  - |
>> +    virtio@3000 {
>> +            compatible = "virtio,mmio";
>> +            reg = <0x3000 0x100>;
>> +            interrupts = <41>;
>> +
>> +            /* The device is located in Xen domain with ID 1 */
>> +            xen,dev-domid = <1>;
>> +    };
>> 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
> No need to define the type again nor describe it again.
>
> Instead, just change additionalProperties to unevaluateProperties in
> this doc. The diff is the latter takes $ref's into account.

ok, will do. Could you please clarify, shall I use?

unevaluatedProperties: false

or

unevaluatedProperties:

type: object


I am not too familiar with this stuff. Both variants seem to pass 
validation.


Thank you.


>
>> +
>>   required:
>>     - compatible
>>     - reg
>> -- 
>> 2.7.4
>>
>>
-- 
Regards,

Oleksandr Tyshchenko