linux-kernel - Re: Regulator supplies when using Device Tree

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Message-ID: <20120330103602.GE21950@opensource.wolfsonmicro.com>
Date:	Fri, 30 Mar 2012 11:36:02 +0100
From:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
To:	Michael Bohan <mbohan@...eaurora.org>
Cc:	rnayak@...com, lrg@...com, LKML <linux-kernel@...r.kernel.org>,
	linux-arm-msm@...r.kernel.org
Subject: Re: Regulator supplies when using Device Tree

On Thu, Mar 29, 2012 at 06:18:44PM -0700, Michael Bohan wrote:
> On 3/29/2012 4:11 AM, Mark Brown wrote:
> >On Wed, Mar 28, 2012 at 05:06:48PM -0700, Michael Bohan wrote:

> >>Are you aware of any other examples of submitted drivers with Device
> >>Tree support that implement regulator devices that optionally have
> >>an upstream supply? I looked at your tree recently and couldn't see
> >>any such cases.

> >No, pretty much any drivers which optionally have an upstream supply
> >would be buggy and should therefore run into trouble during review.

> Can you please elaborate on why this is a bad design? We have always
> used this model in the past, and the regulator framework is happy to
> support it.

The support for regulator-regulator supplies has always been problematic
and infrequently used -

> We have identical hardware blocks that can be positioned to take a
> supply or not. So are you proposing we copy / paste our driver so
> that in one case rdesc->supply_name is NULL and the other case a
> valid supply name? I'm guessing you aren't implying this, but what
> alternatives do you suggest to support such a model?

Please be more specific about what you're actually trying to physically
accomplish here.  It would be *extremely* unusual to see a regulator
which was able to do something useful without any input power and if you
genuinely have this need whatever you're doing probably needs the
framework to actually be aware of what's going on.  However...

> I was hoping that we could continue to treat regulator supplies as
> normal supplies, but somehow allow the framework to determine
> whether a regulator supply exists or not in the Device Tree
> configuration so the driver doesn't have to.

...this doesn't really make any sense - the new scheme makes regulator
supplies *more* like normal supplies, not less, since they're now
specified in exactly the same way as other supplies and are just assumed
to be provided by the leaf driver.

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