Re: [PATCH v2 08/11] dt-bindings: firmware: arm,scmi: Extend bindings for protocol@13

From: Rob Herring <robh@kernel.org>
To: Sudeep Holla <sudeep.holla@arm.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
	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
Subject: Re: [PATCH v2 08/11] dt-bindings: firmware: arm,scmi: Extend bindings for protocol@13
Date: Fri, 21 Jul 2023 08:33:04 -0600	[thread overview]
Message-ID: <20230721143304.GA1092306-robh@kernel.org> (raw)
In-Reply-To: <20230721115535.mx46dg56pxjnzbuv@bogus>

On Fri, Jul 21, 2023 at 12:55:35PM +0100, Sudeep Holla wrote:
> On Fri, Jul 21, 2023 at 01:42:43PM +0200, Ulf Hansson wrote:
> > On Wed, 19 Jul 2023 at 17:17, Sudeep Holla <sudeep.holla@arm.com> wrote:
> > >
> > > On Thu, Jul 13, 2023 at 04:17:35PM +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 domaintoo. The common way to describe this, is to use
> > > > the "power-domain" DT bindings, so let's use that.
> > > >
> > >
> > > One thing I forgot to ask earlier is how we can manage different domain IDs
> > > for perf and power domains which is the case with current SCMI platforms as
> > > the spec never mandated or can ever mandate the perf and power domains IDs
> > > to match. They need not be same anyways.
> > 
> > Based upon what you describe above, I have modelled the perf-domain
> > and the power-domain as two separate power-domain providers.
> > 
> > A consumer device being hooked up to both domains, would specify the
> > domain IDs in the second power-domain-cell, along the lines of the
> > below. Then we would use power-domain-names to specify what each
> > power-domain represents.
> > 
> > power-domains = <&scmi_pd 2>, <&scmi_dvfs 4>;
> > power-domain-names = "power", "perf";
> >
> > I hope this makes it clearer!?
> 
> Yes it make is clear definitely, but it does change the definition of the
> generic binding of the "power-domains" property now. I am interesting in
> the feedback from the binding maintainers with respect to that. Or is it
> already present ? IIUC, the ones supported already are generally both
> power and performance providers. May be it doesn't matter much, just
> wanted to explicit ask and confirm those details.

I commented on v1.

Looks like abuse of "power-domains" to me, but nothing new really. 
Please define when to use a power domain vs. a perf domain and don't 
leave it up to the whims of the platform. Maybe perf domains was a 
mistake and they should be deprecated?

Rob