linux-kernel - Re: [PATCH 2/2] regulator: add mxs regulator driver

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Date:	Tue, 30 Sep 2014 08:40:26 +0200
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Mark Brown <broonie@...nel.org>, shawn.guo@...aro.org,
	festevam@...il.com
CC:	lgirdwood@...il.com, robh+dt@...nel.org, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH 2/2] regulator: add mxs regulator driver

Am 29.09.2014 um 19:13 schrieb Mark Brown:
> On Mon, Sep 29, 2014 at 08:38:51AM +0200, Stefan Wahren wrote:
>
>> I'm searching for a good regulator implementation example.
>> Does it apply to ti-abb-regulator.c and twl-regulator.c?
> Possibly.  But bear in mind that it's important to understand the
> hardware you're trying to support.

The question refer more to the devicetree binding and it's implementation.

>
>>> This really needs a comment to explain what on earth is going on here -
>>> the whole thing with writing the same thing twice with two delays is
>>> more than a little odd.  It looks like the driver is trying to busy wait
>>> in cases where the change happens quickly but the comments about "fast"
>>> and "normal" mode make this unclear.
>> The regulator driver polls for the DC_OK bit in the power status register.
>> Quote for reference manual (p. 935): "High when switching DC-DC
>> converter control loop has stabilized after a voltage target change."
>> The two loops comes from the different regulator modes
>> (REGULATOR_MODE_FAST, REGULATOR_MODE_NORMAL).
>> In REGULATOR_MODE_FAST the voltage steping is disabled and changing
>> voltage should be fast. In REGULATOR_MODE_NORMAL voltage steping is
>> enabled and it's take a while for reaching the target voltage.
> I don't think you've fully understood what the different modes mean
> here, that's not normally how a buck convertor works.  The different
> modes would typically control the ability of the regulator to respond
> quickly to changes in load without drifting off regulation, fast mode
> makes the regulator less efficient but more responsive to load changes
> (probably marginally with modern regulators).  It should have relatively
> little to do with the ability to ramp the voltage and certainly not on
> the scale there.
>
>> Do you see more a problem with the two different loops or the redundant
>> register write?
> Both.  The code right now just looks really obscure.

That leads me to the conclusion to drop both mode functions. My
intention is to get the cpufreq-cpu0 aka cpufreq-dt working on i.MX28,
not to build up the complete power system.

@Fabio, @Shawn: What is your opinion?

Best regards

Stefan


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