[PATCH RFC 2/3] power: mxs_power: add driver for mxs power subsystem

[Stefan Wahren]

Hi Mark,

> Mark Brown <broonie at kernel.org> hat am 27. Januar 2015 um 20:43 geschrieben:
>
>
> On Tue, Jan 27, 2015 at 07:35:09PM +0100, Stefan Wahren wrote:
> > > Mark Brown <broonie at kernel.org> hat am 27. Januar 2015 um 01:16
> > > geschrieben:
>
> > > > okay i understand. But doesn't it need a extra driver to set the
> > > > switching
> > > > frequency because of the new compatible string?
>
> > > I don't understand this bit at all, sorry.
>
> > Sebastian suggested a new sub-node in the devicetree:
>
> > powerpll {
> > compatible = "fsl,imx28-power-pll"
> > #clock-cells = <0>;
> > clock-frequency = <12345>;
> > }
>
> > and i think that the new compatible string needs a separate driver to take
> > care
> > of the switching frequency.
>
> I can see that this has been suggested, what I can't understand is why
> we would wish to do this but I am missing some context here which may
> make it all perfectly clear.

changing the switching frequency is not a common feature for this IC. In most
cases the clock for the DC-DC switching frequency runs at 24 MHz (ref_xtal).
Unfortunatelly this could cause interferences for example in UHF band. So
switching to ref_pll and changing clock divider is a option to avoid such
interferences without changing hardware.

The relevant register DC-DC Miscellaneous Register (HW_POWER_MISC) is described
in chapter 11.12.10 of the reference manual [1].

I decided to implement it as a module parameter, because i see it's a
configuration option.

[1] - http://cache.freescale.com/files/dsp/doc/ref_manual/MCIMX28RM.pdf

>
> > Or is it okay to leave the handling of the switching frequency in the
> > mxs-power
> > driver?
>
> Unless the clock is exposed externally to the regulator either as an
> input or an output I'm not sure I see any benefit but I'm possibly
> missing something here. It does sound like there might be a separate
> clock IP or something?
>
> > Btw if we add a new node to set switching frequency, i think it would be
> > better
> > to describe the dc-dc convertor and not the pll:
>
> > dcdc {
> > compatible = "fsl,imx28-dcdc"
> > frequency = <12345>;
> > }
>
> > What do you think?
>
> Yes, just adding a new property on the regulator node with all the other
> properties seems sensible (we've just gained some helpers which make it
> fairly straightforward to do this).
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