Re: [PATCH 3/3] ARM: dt: tegra: paz00: add regulators

From: Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>
To: Marc Dietrich <marvin24-Mmb7MZpHnFY@public.gmane.org>
Cc: Mark Brown
	<broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>,
	Stephen Warren <swarren-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org>,
	Olof Johansson <olof-nZhT3qVonbNeoWH0uzbU5w@public.gmane.org>,
	Colin Cross <ccross-z5hGa2qSFaRBDgjK7y7TUQ@public.gmane.org>,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 3/3] ARM: dt: tegra: paz00: add regulators
Date: Mon, 25 Jun 2012 13:07:45 +0200	[thread overview]
Message-ID: <20120625110745.GB11710@avionic-0098.mockup.avionic-design.de> (raw)
In-Reply-To: <27366523.LjLfRK1TqH@ax5200p>

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On Sun, Jun 24, 2012 at 03:27:42PM +0200, Marc Dietrich wrote:
> On Sunday 24 June 2012 13:31:51 Mark Brown wrote:
> > On Sun, Jun 24, 2012 at 02:01:58PM +0200, Marc Dietrich wrote:
> > > On Sunday 24 June 2012 12:03:06 Mark Brown wrote:
> > > > > > +                                 	regulator-name = "+3.3vs_ldo0";
> > > > > > +					regulator-max-microvolt = <3300000>;
> > > > 
> > > > This is one example, it looks like the rail needs to be fixed to 3.3V.
> > > 
> > > I think nowhere in the code a regulator (beside sm*) is programmed to some
> > > different value that the maximum given here (this is not the maximum the
> > > regulator can provide). I never understood why the kernel code always sets
> > > the regulator to the maximum value if no other value was specified. IMHO,
> > > there should be some initial value, e.g. regulator-default-microvolt, as
> > > the original driver (from 2.6.32 ages) did. This way the maximum value
> > > can be set
> > That's *never* been in mainline, and nobody even bothered trying to
> > submit it.
> 
> which was the best thing to do ;-)
> 
> > > to the hw limits, but maybe this is a bit dangerous.
> > 
> > One of two things should be happening.  Either a single voltage is
> > specified (in which case that voltage will be configured in the
> 
> I'm not an expert on this, but it seems to me that only sm0 and sm1 should be 
> changeable (and some rail called vdd_aon, which seems to be ldo2 in case of 
> paz00 connected to the rtc). So, all others can be constant voltage. Maybe 
> Stephen can comment on the actual requirements (also for the other boards 
> which may have similar layout).

I can confirm that at least for ldo0 the value needs to be fixed. I did
in fact post a patch back in February that was needed to fix PCIe on
Harmony. I also sat down with one of our hardware engineers and worked
through the list and wrote down the requirements for Harmony. I need to
check where our notes have gone, though.

Thierry

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