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

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Message-ID: <2c196f9a-b61e-914b-1999-e9e82d16dc6e@quicinc.com>
Date:   Thu, 5 Oct 2023 14:51:28 -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 10/4/2023 8:53 AM, Sudeep Holla wrote:
> On Tue, Oct 03, 2023 at 08:59:45AM -0700, Nikunj Kela wrote:
>> 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.
>>
> Let us keep it without shmem. If it is dynamically allocated, you must not
> need another compatible as you can check it at the runtime.
>
>>> 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.
>>
> I think only OPTEE has explicit conduit other than PSCI and it is continued
> for legacy/compatibility reasons IIUC and IIRC. Anything else depends on
> the conduit used by PSCI to be consistent. So yes you need to use what the
> PSCI conduit is and you don't need the extra information from the DT either
> as new property or in the compatible.

Ok, will use conduit then. Thanks!


>