linux-kernel - Re: [PATCH v4 4/4] regulator: Prevent falling too fast

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Message-ID: <20160915143945.GJ27974@sirena.org.uk>
Date:   Thu, 15 Sep 2016 15:39:45 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     lgirdwood@...il.com, Douglas Anderson <dianders@...omium.org>,
        briannorris@...omium.org, javier@...hile0.org, robh+dt@...nel.org,
        mark.rutland@....com, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v4 4/4] regulator: Prevent falling too fast

On Tue, Sep 13, 2016 at 10:21:40AM -0700, Matthias Kaehlcke wrote:

> Optimizing the delay time depends on the SoC; we have not measured
> this across a wide variety of devices and thus have very conservative
> numbers. The percentage is based on the trigger for OVP on the
> regulator. In this case, OVP kicks in when the FB node is 20% over
> regulation, which is equivalent to a 16% drop in voltage (1/1.2). For
> our device safe-fall-percent is set to 16 and slowest-decay-rate is
> 225.

The obvious question here is how the OVP hardware knows about the new
voltage and why we're bodging this in the regulator core rather than in
the OVP hardware.

> > I'd like to see some more thorough analysis than just an "apparently"
> > here.  It's making the code more fiddly for something very handwavy.

> It's well-understood why it's a percentage. DVS is controlled by
> offsetting the FB current, and as above, OVP is based on how far you
> are from the FB target.

You might think you understand this clearly but nobody reading the
commit message or looking at the code later on is going to be able
do so when your commit message only contains vague handwaving.

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