Hi Mark,

Mark Brown [off-list ref] hat am 27. Januar 2015 um 20:43 geschrieben:


On Tue, Jan 27, 2015 at 07:35:09PM +0100, Stefan Wahren wrote:

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Mark Brown [off-list ref] hat am 27. Januar 2015 um 01:16
geschrieben:

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okay i understand. But doesn't it need a extra driver to set the
switching
frequency because of the new compatible string?

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I don't understand this bit at all, sorry.

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Sebastian suggested a new sub-node in the devicetree:

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powerpll {
compatible = "fsl,imx28-power-pll"
#clock-cells = <0>;
clock-frequency = <12345>;
}

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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

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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?

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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:

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dcdc {
compatible = "fsl,imx28-dcdc"
frequency = <12345>;
}

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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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