linux-kernel - Re: [PATCH] regulator: arizona-ldo1: Add ramp time for HI

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Date:	Tue, 24 Mar 2015 17:05:34 +0000
From:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	patches@...nsource.wolfsonmicro.com, lgirdwood@...il.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] regulator: arizona-ldo1: Add ramp time for HI_PWR

On Tue, Mar 24, 2015 at 04:40:50PM +0000, Charles Keepax wrote:
> On Tue, Mar 24, 2015 at 09:06:09AM -0700, Mark Brown wrote:
> > On Tue, Mar 24, 2015 at 02:27:56PM +0000, Charles Keepax wrote:
> > 
> > > +static int arizona_ldo1_hc_set_voltage_time_sel(struct regulator_dev *rdev,
> > > +						unsigned int old_selector,
> > > +						unsigned int new_selector)
> > > +{
> > > +	/* if moving to 1.8v allow time for it to reach voltage */
> > > +	if (new_selector == rdev->desc->n_voltages - 1)
> > > +		return 25;
> > > +	else
> > > +		return 0;
> > > +}
> > 
> > So changes to move to the top voltage always take constant time while
> > all other voltage changes are instantaneous?  That doesn't seem right.
> > I'd expect something more like a calculation based on some number of
> > miliseconds per milivolt.
> 
> Its more just that this is the only case that we really care
> about. The reg only ever gets used at 1.2V and 1.8V, and the
> only case where there is a problem is if we ask for 1.8V and
> we don't have it yet.
> 
> I don't think we really have the data to give for other cases. I
> could expand the comment perhaps? Or TBH it is fast enough it is
> unlikely to ever be a problem in practice so we could just drop
> the patch.

Oh, I had one other thought, what about if we just returned 25uS
as a worse case for the transition. Perhaps that would be nicer,
and the 1.2V -> 1.8V transition is almost certainly the slowest
of the options available.

Thanks,
Charles
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