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

[icenowy]

å 2017-07-26 19:44ïMaxime Ripard åéï
> Hi,
>
> On Wed, Jul 26, 2017 at 12:23:48PM +0200, OndÅej Jirman wrote:
> > Hi,
> >
> > icenowy@xxxxxxx pÃÅe 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 seems that in regulator_desc structure a default value of ramp delay
can be set, and the ones specified in dt can override it.

So just add .ramp_delay = 200 in the driver's regulator_desc part?

Should a comment be added that explains it's only an experienced value
on Allwinner H3/H5 boards VDD-CPUX usage?

> Maxime
>
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