Re: [RESEND PATCH 1/2] dt-bindings: firmware: arm,scmi: define support for name based regulators

From: Mark Brown <broonie@kernel.org>
To: David Collins <quic_collinsd@quicinc.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	devicetree@vger.kernel.org, Liam Girdwood <lgirdwood@gmail.com>,
	Cristian Marussi <cristian.marussi@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	Subbaraman Narayanamurthy <quic_subbaram@quicinc.com>
Subject: Re: [RESEND PATCH 1/2] dt-bindings: firmware: arm,scmi: define support for name based regulators
Date: Wed, 2 Feb 2022 17:38:13 +0000	[thread overview]
Message-ID: <YfrBharI91QYkPR1@sirena.org.uk> (raw)
In-Reply-To: <8355035c-6d90-adfd-c4e1-7bb37a2d8055@quicinc.com>

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On Fri, Jan 28, 2022 at 03:09:30PM -0800, David Collins wrote:
> On 1/28/22 11:32 AM, Mark Brown wrote:
> > On Mon, Jan 24, 2022 at 04:27:35PM -0800, David Collins wrote:

> >> Name based SCMI regulator specification helps ensure that an SCMI
> >> agent doesn't need to be aware of the numbering scheme used for

> > What is a "SCMI agent" in this context?  This is changing how the DT
> > bindings are specified, at some point things are going to need to be
> > hard coded.

> The system layout that this patch is targeted for consists of an SCMI
> platform implemented in software in the primary Linux OS on the
> application processor and an SCMI agent in a guest VM (also running
> Linux).  This provides paravirtualized regulator control to the guest VM
> where full virtualization is not supported.

> During the course of development of these software images, it may be
> necessary to add or reorder the set of SCMI voltage domains (regulators)
> implemented on the platform side.  If the voltage domains are only
> identified and matched based on the ID number, then it is easy for the
> platform and agent to get out of sync.

> Using the voltage domain name instead of ID number for identification
> and matching provides robust assurance of correct regulator usage in the
> face of domains being added, removed, or reordered on the platform side.

This seems like a scenario where the DT should be being generated at
runtime along with the virtualisation of the platform?  TBH a setup
where this is an issue feels like it's asking for trouble.

> >> +              regulator-name: true

> > This is abusing the existing regulator-name property which is there to
> > allow a human readable descriptive string to be attached to a regulator.
> > It should have no effect other than being included in diagnostic output.

> Would you be ok with a new DT property being added in place of
> "regulator-name" in this patch which serves the same matching purpose
> (perhaps "arm,scmi-domain-name")?

Yes, it needs to be a new property.

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