linux-kernel - Re: [PATCH v3 1/9] dt-bindings: host1x: Add memory-contexts property

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Date:   Mon, 21 Feb 2022 17:28:39 +0200
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Robin Murphy <robin.murphy@....com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        thierry.reding@...il.com, jonathanh@...dia.com, joro@...tes.org,
        will@...nel.org, robh+dt@...nel.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/9] dt-bindings: host1x: Add memory-contexts property

On 2/21/22 17:23, Robin Murphy wrote:
> On 2022-02-18 11:39, Mikko Perttunen via iommu wrote:
>> Add schema information for the memory-contexts property used to
>> specify context stream IDs. This uses the standard iommu-map property
>> inside a child node.
> 
> Couldn't you simply make "iommu-map" an allowed property on the host1x 
> node itself? From a DT perspective I'm not sure the intermediate node 
> really fits meaningfully, and I can't see that it serves much purpose in 
> practice either, other than perhaps defeating fw_devlink.
> 
> Robin.

The stream IDs described here are not used by the host1x device itself, 
so I don't think I can. Host1x's memory transactions still go through 
the stream ID specified in its 'iommus' property, these stream IDs are 
used by engines (typically in addition to the stream ID specified in 
their own nodes).

Host1x 'iommus' -- Channel commands
Engine 'iommus' -- Engine firmware (and data if context isolation is not 
enabled)
memory-contexts 'iommu-map' -- Data used by engines.

(Perhaps I should add this information to various places in more 
abundance and clarity.)

Mikko

> 
>> Signed-off-by: Mikko Perttunen <mperttunen@...dia.com>
>> ---
>> v3:
>> * New patch
>> ---
>>   .../bindings/display/tegra/nvidia,tegra20-host1x.yaml  | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git 
>> a/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.yaml 
>> b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.yaml 
>>
>> index 4fd513efb0f7..3ac0fde54a16 100644
>> --- 
>> a/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.yaml 
>>
>> +++ 
>> b/Documentation/devicetree/bindings/display/tegra/nvidia,tegra20-host1x.yaml 
>>
>> @@ -144,6 +144,16 @@ allOf:
>>           reset-names:
>>             maxItems: 1
>> +        memory-contexts:
>> +          type: object
>> +          properties:
>> +            iommu-map:
>> +              description: Specification of stream IDs available for 
>> memory context device
>> +                use. Should be a mapping of IDs 0..n to IOMMU entries 
>> corresponding to
>> +                usable stream IDs.
>> +          required:
>> +            - iommu-map
>> +
>>         required:
>>           - reg-names