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    SubjectRe: [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@aosc.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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