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

[Nikunj Kela]

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@xxxxxxxxxxx>
> > > > Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> > > > ---
> > > >    .../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!


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