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

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Date:	Wed, 1 Oct 2014 15:23:44 +0200 (CEST)
From:	Stefan Wahren <stefan.wahren@...e.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	kernel@...gutronix.de, pawel.moll@....com, lgirdwood@...il.com,
	robh+dt@...nel.org, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux-kernel@...r.kernel.org,
	shawn.guo@...aro.org, festevam@...il.com, mark.rutland@....com,
	devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] regulator: add mxs regulator driver

Hi Mark,

> Mark Brown <broonie@...nel.org> hat am 29. September 2014 um 19:13
> geschrieben:
>
> > > 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.
>

thanks for your explanation.

Is it better to let the core handles the ramp delay instead of set_voltage_sel
with a busy wait?

I've found that polling DC_OK is only reliable for increasing voltages. So i
think about defining ramp delay in the regulator description.

Stefan
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