linux-kernel - Re: [PATCH 07/17] mfd: sec-common: Instantiate s2mpg10 bucks and ldos separately

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Message-ID: <17434d4ceae1e65a5151bb1308b8e49dbbdaf021.camel@linaro.org>
Date: Fri, 13 Jun 2025 15:52:49 +0100
From: André Draszik <andre.draszik@...aro.org>
To: Lee Jones <lee@...nel.org>
Cc: Tudor Ambarus <tudor.ambarus@...aro.org>, Rob Herring <robh@...nel.org>,
  Conor Dooley <conor+dt@...nel.org>, Krzysztof Kozlowski <krzk@...nel.org>,
 Liam Girdwood <lgirdwood@...il.com>,  Mark Brown <broonie@...nel.org>,
 Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski	
 <brgl@...ev.pl>, Peter Griffin <peter.griffin@...aro.org>, Will McVicker	
 <willmcvicker@...gle.com>, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org, linux-samsung-soc@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 07/17] mfd: sec-common: Instantiate s2mpg10 bucks and
 ldos separately

On Fri, 2025-06-13 at 15:49 +0100, André Draszik wrote:
> Hi Lee,
> 
> Thanks for your review!
> 
> On Fri, 2025-06-13 at 15:19 +0100, Lee Jones wrote:
> > On Wed, 04 Jun 2025, André Draszik wrote:
> > 
> > > Bucks can conceivably be used as supplies for LDOs, which means we need
> > > to instantiate them separately from each other so that the supply-
> > > consumer links can be resolved successfully at probe time.
> > > 
> > > By doing so, the kernel will defer and retry instantiating the LDOs
> > > once BUCKs have been created while without this change, it can be
> > > impossible to mark BUCKs as LDO supplies. This becomes particularly
> > > an issue with the upcoming support for the S2MPG11 PMIC, where
> > > typically certain S2MP10/11 buck rails supply certain S2MP11/10 LDO
> > > rails.
> > > 
> > > The platform_device's ::id field is used to inform the regulator driver
> > > which type of regulators (buck or ldo) to instantiate.
> > 
> > I'm confused.
> > 
> > There is nothing that differentiates the two, so why do you need to?
> 
> On gs101, we have two PMICs, s2mpg10 and s2mpg11. Several s2mpg10 LDOs
> are consumers of various s2mpg10 bucks & s2mpg10 bucks, and several

Small typo, should read:

... Several s2mpg10 LDOs are consumers of various s2mpg10 bucks & s2mpg11
bucks...

> s2mpg11 LDOs are also supplied by various s2mpg10 bucks & s2mpg11 bucks.
> 
> So we have a circular dependency here. LDOs of one PMIC depend on bucks
> of the other.
> 
> If all s2mpg10 rails are handled by the same instance of the s2mpg10
> regulator driver, probe will defer (and ultimately fail), because the
> supplies to the LDOs can not be resolved during probe.
> 
> The same goes for s2mpg11.
> 
> The result is that neither driver can probe successfully (unless you're
> _extremely_ lucky due to parallel probing, but we can not rely on that,
> of course).
> 
> By splitting LDO and buck rails into separate instances, this circular
> dependency is gone, the buck-instance of each respective driver can probe,
> which then allows the LDO instance of the other driver to probe.
> 
> Does that answer the question, or did I misunderstand it?
> 
> 
> Cheers,
> Andre'