linux-kernel - Re: [linux-sunxi] [PATCH 10/10] ARM: dts: sun8i: Add SY8106A regulator to Orange Pi PC

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Message-ID: <1501073680.20056.3.camel@megous.com>
Date:   Wed, 26 Jul 2017 14:54:40 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     maxime.ripard@...e-electrons.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

Maxime Ripard píše v St 26. 07. 2017 v 13:44 +0200:
> 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.

It translates to 1ms per 0.2V which is highly conservative. The real
times will be in 1-10us range. So I guess this could be a default in
the driver.

regards,
  o.

> Maxime
> 
> -- 
> Maxime Ripard, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com
> 
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