linux-kernel - Re: [PATCH v4 3/4] dt-bindings: arm: Add new compatible for smc/hvc transport for SCMI

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Date:   Tue, 3 Oct 2023 08:59:45 -0700
From:   Nikunj Kela <quic_nkela@...cinc.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     <cristian.marussi@....com>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v4 3/4] dt-bindings: arm: Add new compatible for smc/hvc
 transport for SCMI


On 10/3/2023 3:44 AM, Sudeep Holla wrote:
> On Mon, Sep 11, 2023 at 12:43:58PM -0700, Nikunj Kela wrote:
>> Introduce compatible "qcom,scmi-hvc-shmem" for SCMI smc/hvc
>> transport channel for Qualcomm virtual platforms.
>> The compatible mandates a shared memory channel.
>>
>> Signed-off-by: Nikunj Kela <quic_nkela@...cinc.com>
>> Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> ---
>>   .../devicetree/bindings/firmware/arm,scmi.yaml       | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
>> index 8d54ea768d38..4090240f45b1 100644
>> --- a/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
>> +++ b/Documentation/devicetree/bindings/firmware/arm,scmi.yaml
>> @@ -45,6 +45,9 @@ properties:
>>         - description: SCMI compliant firmware with OP-TEE transport
>>           items:
>>             - const: linaro,scmi-optee
>> +      - description: SCMI compliant firmware with Qualcomm hvc/shmem transport
>> +        items:
>> +          - const: qcom,scmi-hvc-shmem
> Can it be simply "qcom,scmi-smc" for 2 reasons ?
> 1. We don't support SMC/HVC without shmem, so what is your argument to add
>     '-shmem' in the compatible here ?

In our platforms, there are multiple ways to allocate memory. One is 
preallocated shmem as used here, another is dynamically by hypervisor 
APIs. shmem was to just to indicate it is preallocated.


> 2. The exact conduit(SMC/HVC) used is detected runtime, so I prefer to keep
>    '-smc' instead of '-hvc' in the compatible just to avoid giving an illusion
>    that HVC is the conduit chosen here based on the compatible. It can be true
>    for other reason but I don't want to mislead here by using HVC.

IUUC, currently, conduit comes from PSCI dt node. We have been using smc 
for PSCI but want to use hvc here. That being said, I am fine to explore 
if we can change PSCI to use hvc too.


>>     interrupts:
>>       description:
>> @@ -320,6 +323,15 @@ allOf:
>>         required:
>>           - linaro,optee-channel-id
>>   
>> +  - if:
>> +      properties:
>> +        compatible:
>> +          contains:
>> +            const: qcom,scmi-hvc-shmem
>> +    then:
>> +      required:
>> +        - shmem
>> +
>>   examples:
>>     - |
>>       firmware {
>> -- 
>> 2.17.1
>>