linux-kernel - Re: [PATCH 1/2] dt-bindings: arm,scmi: Do not use clocks for SCMI performance domains

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Message-ID: <20201021163021.lkqhum3xnyzt6pir@bogus>
Date:   Wed, 21 Oct 2020 17:30:21 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 1/2] dt-bindings: arm,scmi: Do not use clocks for SCMI
 performance domains

On Wed, Oct 21, 2020 at 11:20:27AM -0500, Rob Herring wrote:
> On Tue, Oct 20, 2020 at 3:37 PM Sudeep Holla <sudeep.holla@....com> wrote:
> >
> > Commit dd461cd9183f ("opp: Allow dev_pm_opp_get_opp_table() to return
> > -EPROBE_DEFER") handles -EPROBE_DEFER for the clock/interconnects within
> > _allocate_opp_table() which is called from dev_pm_opp_add and it
> > now propagates the error back to the caller.
> >
> > SCMI performance domain re-used clock bindings to keep it simple. However
> > with the above mentioned change, if clock property is present in a device
> > node, opps can't be added until clk_get succeeds. So in order to fix the
> > issue, we can register dummy clocks which is completely ugly.
> >
> > Since there are no upstream users for the SCMI performance domain clock
> > bindings, let us introduce separate performance domain bindings for the
> > same.
> >
> > Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> > ---
> >  .../devicetree/bindings/arm/arm,scmi.txt      | 19 ++++++++++++++++---
> >  1 file changed, 16 insertions(+), 3 deletions(-)
> >
> > Hi Rob/Viresh,
> >
> > This is actually a fix for the regression I reported here[1].
> > I am not adding fixes tag as I am targeting in the same release and
> > also because it is not directly related.
> >
> > Regards,
> > Sudeep
> >
> > [1] https://lore.kernel.org/r/20201015180555.gacdzkofpibkdn2e@bogus
> >
> > P.S.:/me records that this binding needs to be moved to yaml in v5.11
> >
> > diff --git a/Documentation/devicetree/bindings/arm/arm,scmi.txt b/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > index 55deb68230eb..0a6c1b495403 100644
> > --- a/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > +++ b/Documentation/devicetree/bindings/arm/arm,scmi.txt
> > @@ -44,7 +44,7 @@ as described in the following sections. If the platform supports dedicated
> >  mboxes, mbox-names and shmem shall be present in the sub-node corresponding
> >  to that protocol.
> >
> > -Clock/Performance bindings for the clocks/OPPs based on SCMI Message Protocol
> > +Clock bindings for the clocks based on SCMI Message Protocol
> >  ------------------------------------------------------------
> >
> >  This binding uses the common clock binding[1].
> > @@ -52,6 +52,19 @@ This binding uses the common clock binding[1].
> >  Required properties:
> >  - #clock-cells : Should be 1. Contains the Clock ID value used by SCMI commands.
> >
> > +Performance bindings for the OPPs based on SCMI Message Protocol
> > +------------------------------------------------------------
> > +
> > +Required properties:
> > +- #perf-domain-cells: Should be 1. Contains the performance domain ID value
> > +                     used by SCMI commands.
>
> When is this not 1 (IOW, you only need this if variable)? How would it
> be used outside SCMI (given it has a generic name)?
>

Ah, I thought we need this if phandle is followed by 1 or more arguments.
If it is not compulsory I can drop this or make it scmi specific if we
need it.

> > +
> > +* Property arm,scmi-perf-domain
>
> Yet this doesn't have a generic name. You mentioned on IRC this is
> aligned with QCom, but why can't QCom use the same property here?
>

This is SCMI firmware driven while they have hardware driven perf/freq
domains. So different drivers, need to distinguish between the two.

> Really though, why can't you give SCMI a CPUs MPIDR and get its domain?

Not a bad idea, will check if we can add this to the future specification.
Anyways we still need something with existing version of the spec.

--
Regards,
Sudeep