[U-Boot] [PATCH v3 6/9] regulator: Add support for ramp delay

[Torsten Duwe <duwe@lst.de>]

On Mon, Feb 18, 2019 at 03:28:46PM +0100, Krzysztof Kozlowski wrote:
> On Mon, 18 Feb 2019 at 15:03, Torsten Duwe <duwe@lst.de> wrote:
> >
> > > --- a/doc/device-tree-bindings/regulator/regulator.txt
> > > +++ b/doc/device-tree-bindings/regulator/regulator.txt
> > > @@ -35,6 +35,7 @@ Optional properties:
> > >  - regulator-max-microamp: a maximum allowed Current value
> > >  - regulator-always-on: regulator should never be disabled
> > >  - regulator-boot-on: enabled by bootloader/firmware
> > > +- regulator-ramp-delay: ramp delay for regulator (in uV/us)
> >
> > I guess you mean s/V, not V/s; at least the code suggests so.
> 
> uV/uS. It is correct in the code:
> int delay = DIV_ROUND_UP(abs(new_uV - old_uV), ramp_delay);
> delay = (uV - uV) / (uV / uS) = uS

You're right. _divide_ by that value; somhow this has escaped me.
Sorry for the noise.

nit: "s" is for seconds, "S" is for conductance.

> > But my main point is: is the required delay always a linear
> > function of the voltage jump? Depending on the dampening and
> > load on the rail this could be an overshoot and settle, no?
> >
> > So I suggest to make that an array with 2 elements: a fixed part
> > and a time per voltage change. Does that make sense?
> 
> Just to make it clear - then we do not follow Linux kernel DT bindings.
> The voltage change might have exponential characteristic and/or have
> additional fixed delay time (see patch 7 here). We could re-use some
> properties from Linux bindings for that purpose:
> https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/regulator/regulator.txt#L19
> https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/regulator/regulator.txt#L24

I see. But then "static void regulator_set_value_delay(...)" should either
at least have a "ramp" somewhere in its name or it should discover the device
properties on its own, in order to be able to handle regulator-settling-time*
and regulator-enable-ramp-delay as well in the future. (i.e. pass it uc_pdata
instead of uc_pdata->ramp_delay and also let it handle the condition).

	Torsten