linux-kernel - DVS regulator drivers

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Date:	Mon, 19 Nov 2012 12:52:09 +0100 (CET)
From:	Guennadi Liakhovetski <g.liakhovetski@....de>
To:	linux-kernel@...r.kernel.org
cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>
Subject: DVS regulator drivers

As I mentioned in an earlier mail today [1] I have a difficulty seeing how 
the current regulator API can efficiently be used for DVS-type regulators. 
Trying to look at existing mainline drivers it seems to me they try to 
guess, what the user really wants, do that differently and don't manage to 
do that in a bug-free way. Specifically, I looked at 2 drivers:

wm831x-dcdc.c handles 2 voltages: "DVS" and "ON." If the new voltage in 
.set_voltage_sel() is equal to one of them, it is just used. If it is a 
new voltage, there's a comment in the driver in 
wm831x_buckv_set_voltage_sel():

	/* Always set the ON status to the minimum voltage */

but I actually don't see, where the minimum is selected. It seems instead 
in this case the "ON" value is just set:

	ret = wm831x_set_bits(wm831x, on_reg, WM831X_DC1_ON_VSEL_MASK, vsel);
	if (ret < 0)
		return ret;
	dcdc->on_vsel = vsel;

Then it goes on to actually switch the output voltage to this new "ON" 
value and then:

	/*
	 * If this VSEL is higher than the last one we've seen then
	 * remember it as the DVS VSEL.  This is optimised for CPUfreq
	 * usage where we want to get to the highest voltage very
	 * quickly.
	 */
	if (vsel > dcdc->dvs_vsel) {
		ret = wm831x_set_bits(wm831x, dvs_reg,
				      WM831X_DC1_DVS_VSEL_MASK,
				      dcdc->dvs_vsel);

Above the _old_ DVS value is set again?

		if (ret == 0)
			dcdc->dvs_vsel = vsel;

Now .dvs_vsel is set - after the voltage has been set to the old value. 
And now both - ON and DVS values are equal to the same value - vsel?... 
Confused.

lp872x.c seems to be selecting between ON and DVS (or V1 and V2 in lp872x' 
terminology) in lp872x_set_dvs(), which is called every time a voltage is 
set. But this function always gets the same arguments - supplied from the 
platform data and therefore only one voltage is ever used... The two 
"dynamic" DVS selection fields in struct lp872x: .dvs_pin and .dvs_gpio 
seem just to always stay constant, the latter is also just initialised 
once and is never used again.

Again, I don't have those devices, so I cannot test and would be a bit 
hesitant to provide patches, but that's my impression from just looking at 
them.

Thanks
Guennadi

[1] https://lkml.org/lkml/2012/11/19/169
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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