linux-kernel - Re: [RESEND PATCH v1 1/2] dt-bindings: misc: fastrpc: add fastrpc group IDs property

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Message-ID: <093c23a6-1c0f-6e86-3abb-a8267ebeed52@linaro.org>
Date:   Thu, 8 Jun 2023 13:33:21 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Ekansh Gupta <quic_ekangupt@...cinc.com>,
        srinivas.kandagatla@...aro.org, linux-arm-msm@...r.kernel.org
Cc:     ekangupt@....qualcomm.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, fastrpc.upstream@....qualcomm.com,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, devicetree@...r.kernel.org
Subject: Re: [RESEND PATCH v1 1/2] dt-bindings: misc: fastrpc: add fastrpc
 group IDs property

On 08/06/2023 12:36, Ekansh Gupta wrote:
> 
> 
> On 6/8/2023 12:14 AM, Krzysztof Kozlowski wrote:
>> On 07/06/2023 18:30, Ekansh Gupta wrote:
>>> Add "qcom,fastrpc-gids" property to the list of optional properties.
>>> This property contains the list of privileged group IDs which is
>>> used to offload process to remote subsystem with increased privileges.
>>
>> Why or when anyone would use this property?
>>
> This property can be used for the use cases which requires prioritized 
> access to remote subsystem resources.

This does not help me much yet.... Which systems or boards need
prioritized access?

>>>
>>> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
>>> ---
>>>   Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml | 6 ++++++
>>>   1 file changed, 6 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml b/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
>>> index 1ab9588..2a2124f 100644
>>> --- a/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
>>> +++ b/Documentation/devicetree/bindings/misc/qcom,fastrpc.yaml
>>> @@ -57,6 +57,11 @@ properties:
>>>         Virtual machine IDs for remote processor.
>>>       $ref: "/schemas/types.yaml#/definitions/uint32-array"
>>>   
>>> +  qcom,fastrpc-gids:
>>> +    description:
>>> +      Group IDs for fastrpc.
>>
>> You just pasted here property name. It does not help me to understand
>> what's this. Explain in description.
>>
> I'll add more details here when I re-submit the patch.
>>> +    $ref: "/schemas/types.yaml#/definitions/uint32-array"
>>
>> Drop quotes.
>>
>> missing min/maxItems.
>>
> I'll update this in v2. Thanks for reviewing.
>>> +
>>>     "#address-cells":
>>>       const: 1
>>>   
>>> @@ -120,6 +125,7 @@ examples:
>>>               qcom,glink-channels = "fastrpcglink-apps-dsp";
>>>               label = "sdsp";
>>>               qcom,non-secure-domain;
>>> +            qcom,fastrpc-gids = <2908>
>>
>> Eh, what does 2908 stands for? Why not 3012 or 1842? How anyone can
>> figure this out?
>>
> There is no hard restriction for this value to be 2908, it can be 
> anything. Just that the process which needs a privileged offload to any 
> remote subsystem should have the same gid which is defined here, whether 
> it is 2908 or anything else.
> 
> The intention of having 2908 in example is because this is used in 
> Android world where any process running with 2908 gid can offload as 
> privileged process to remote subsystem.
> Ref: 
> https://review.lineageos.org/c/LineageOS/android_device_motorola_sm7250-common/+/305612/4/config.fs
> 
> But, it can be set to anything just that the process also needs to adapt 
> to this gid.

So this is process ID? Group ID? GID? Why would you ever encode group
IDs, which change in every installation, or process IDs, which change
every boot, in DTS common for all devices?

This is not a DT property.

Best regards,
Krzysztof