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

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Message-ID: <20150324164050.GI23705@opensource.wolfsonmicro.com>
Date:	Tue, 24 Mar 2015 16:40:50 +0000
From:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	lgirdwood@...il.com, linux-kernel@...r.kernel.org,
	patches@...nsource.wolfsonmicro.com
Subject: Re: [PATCH] regulator: arizona-ldo1: Add ramp time for HI_PWR

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.

Thanks,
Charles
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