linux-kernel - Re: [PATCH v2 3/3] regulator: axp20x: Fix axp22x ldo

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Date:	Wed, 27 Apr 2016 17:30:08 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Hans de Goede <hdegoede@...hat.com>
Cc:	Liam Girdwood <lgirdwood@...il.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] regulator: axp20x: Fix axp22x ldo_io registration
 error on cold boot

On Wed, Apr 27, 2016 at 06:04:53PM +0200, Hans de Goede wrote:
> On 27-04-16 17:48, Mark Brown wrote:

> >Well, I guess someone can just measure what happens?

> What happens will likely depend on the pmic input voltage,
> which can be either 5V from a charger / usb or can be approx
> 3.8V from a lion or lipo battery. All linear regulators in
> the axp20x / axp22x pmic are listed as having a max output
> voltage of 3.3V, this likely has to do with the minimum
> voltage drop compared to the input value.

That sounds like it's a non-regulating bypass mode which is something we
support; if the regulator is in bypass mode we'll look for the voltage
from the parent rather than in the child regulator.

> So in some conditions the output voltage at a 0x1f register
> value may very well be different then at others. IMHO we
> should just avoid any out of spec. values.

As I've said before it'll be read only unless the system integrator
explicitly says otherwise.

> I believe that we really need to write an in-spec value to the
> register controlling the voltage, before enabling this regulator
> (which is done by selecting the mux to connect it to the pin).

We have a strong policy that we don't touch the hardware unless we are
explicitly told it's OK to do so by the system integration, it's very
hard to tell if things are in general going to be safe and if we get
things wrong that could lead to physical damage.

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