linux-kernel - Re: [PATCH 3/5] regulator: axp20x: Update the bindings to use a local parent regulator

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Date:	Fri, 6 Jun 2014 18:05:52 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	carlo@...one.org, Boris Brezillon <boris@...e-electrons.com>,
	lgirdwood@...il.com, lee.jones@...aro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	kevin.z.m.zh@...il.com, sunny@...winnertech.com,
	shuge@...winnertech.com, zhuzhenhua@...winnertech.com
Subject: Re: [PATCH 3/5] regulator: axp20x: Update the bindings to use a
 local parent regulator

On Thu, Jun 05, 2014 at 04:49:31PM +0100, Mark Brown wrote:
> On Thu, Jun 05, 2014 at 04:27:29PM +0200, Maxime Ripard wrote:
> 
> > You already list the regulators available and their supply in the
> > regulator driver, why do you need to set the regulator parents in the
> > mfd driver as well?
> 
> Unless they're being used by the MFD directly there should be no need
> for the MFD to know anything about the supplies.

Ok.

> > My guess is that it's to work around the fact that
> > regulator_dev_lookup only looks for the regulator's device of_node (so
> > not the PMIC one, but one of its child), which doesn't have the supply
> > properties, and then just falls back on the regulator alias
> > list. Would it make some sense to add a lookup in the parent device
> > of_node (which would be the "main" PMIC node in our case)?
> 
> This sounds like you are passing the MFD child device into the regulator
> API when you should be passing the parent device in.

We're passing the device coming from the platform_device that is
passed in probe, that has been created by mfd_add_device, which is
indeed the child device from the MFD device. So we should always use
the platform device parent's instead?

> > Also, there's also the fact that all the supply properties seems to
> > also be mandatory in the DT, even though the regulator itself might
> > not be used at all on the board, and the input voltage not wired to
> > anything.
> 
> For electrical engineering reasons it's unlikely that the supplies are
> actually floating but yes, they are mandatory.  This is an issue with
> registering one device for the entire regulator subsystem on the PMIC,
> it interacts somewhat poorly with deferred probe.  However for systems
> with full constraints like DT and ACPI ones it should be mostly
> sidestepped since the if there is no supply mapped a dummy supply will
> be substituted.

Yes, they are actually tied to the ground, but it's still something
meaningless, that I guess shouldn't be expressed in the DT?

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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