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Message-ID: <20170726114420.ipirqgbluqmggcjy@flea>
Date: Wed, 26 Jul 2017 13:44:20 +0200
From: Maxime Ripard <maxime.ripard@...e-electrons.com>
To: Ondřej Jirman <megous@...ous.com>
Cc: icenowy@...c.io, wens@...e.org,
Liam Girdwood <lgirdwood@...il.com>,
Mark Brown <broonie@...nel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
devicetree <devicetree@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
linux-clk <linux-clk@...r.kernel.org>,
"open list:THERMAL" <linux-pm@...r.kernel.org>,
linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 10/10] ARM: dts: sun8i: Add SY8106A
regulator to Orange Pi PC
Hi,
On Wed, Jul 26, 2017 at 12:23:48PM +0200, Ondřej Jirman wrote:
> Hi,
>
> icenowy@...c.io píše v St 26. 07. 2017 v 15:36 +0800:
> >
> > > > >
> > > > > Otherwse
> > > > >
> > > > > > + regulator-max-microvolt = <1400000>;
> > > > > > + regulator-ramp-delay = <200>;
> > > > >
> > > > > Is this an actual constraint of the SoC? Or is it a characteristic
> > > > > of the regulator? If it is the latter, it belongs in the driver.
> > > > > AFAIK the regulator supports varying the ramp delay (slew rate).
> >
> > I don't know...
> >
> > Maybe I should ask Ondrej?
>
> It is probably neither.
>
> It is used to calculate a delay inserted by the kernel between setting
> a new target voltage over I2C and changing the frequency of the CPU.
> The actual delay is calculated by the difference between previous and
> the new voltage.
>
> I don't remember seeing anything in the datasheet of the regulator.
> This is just some low value that works.
>
> It would probably be dependent on the capacitance on the output of the
> regulator, actual load (which varies), etc. So it is a board specific
> value. One could measure it with an oscilloscope if there's a need to
> optimize this.
If this is a reasonable default, then this should be in the
driver. You can't expect anyone to properly calculate a ramp delay and
have access to both a scope and the CPU power lines.
Maxime
--
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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