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From:   Rob Herring <robh@kernel.org>
Date:   Fri, 14 Jul 2023 11:14:50 -0600
Message-ID: <CAL_Jsq+GMA62hey6+KYMmVSWsDEkGfD0B=0V9AbdmRqdE6VW1g@mail.gmail.com>
Subject: Re: [PATCH 09/16] dt-bindings: firmware: arm,scmi: Extend bindings
 for protocol@13
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Sudeep Holla <sudeep.holla@arm.com>,
        Cristian Marussi <cristian.marussi@arm.com>,
        Viresh Kumar <vireshk@kernel.org>, Nishanth Menon <nm@ti.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Nikunj Kela <nkela@quicinc.com>,
        Prasad Sodagudi <psodagud@quicinc.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>, devicetree@vger.kernel.org
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On Thu, Jun 15, 2023 at 3:11=E2=80=AFAM Ulf Hansson <ulf.hansson@linaro.org=
> wrote:
>
> On Thu, 15 Jun 2023 at 01:00, Rob Herring <robh@kernel.org> wrote:
> >
> > On Wed, Jun 07, 2023 at 02:46:21PM +0200, Ulf Hansson wrote:
> > > The protocol@13 node is describing the performance scaling option for=
 the
> > > ARM SCMI interface, as a clock provider. This is unnecessary limiting=
, as
> > > performance scaling is in many cases not limited to switching a clock=
's
> > > frequency.
> > >
> > > Therefore, let's extend the binding so the interface can be modelled =
as a
> > > generic "performance domain" too. The common way to describe this, is=
 to
> > > use the "power-domain" bindings, so let's use that.
> >
> > What's wrong with the performance-domain binding?
>
> In my opinion I think the performance-domain binding is superfluous.
> We already have plenty of power-domains that do performance scaling
> too - and they stick with the power-domain binding, as it's
> sufficient.

IMO, power-domains should be for power islands which can be power
gated. I know they are abused though. Of course, when things are
hidden in firmware, you don't really know. A power-domain could be
just a clock or a clock could be multiple physical clocks.

> That said, I would rather follow the defacto standard that has been
> used for many years in the kernel. Do you have a preference that we
> should stick to?

If power-domains are sufficient, then why do we have
performance-domains? We need clear rules for when to use what.

Rob