linux-kernel - Re: [PATCH v2 0/9] regulator: pwm-regulator: Introduce continuous-mode

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Message-ID: <20150709172038.GA12199@x1>
Date:	Thu, 9 Jul 2015 18:20:38 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Doug Anderson <dianders@...gle.com>
Cc:	Boris Brezillon <boris.brezillon@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>, kernel@...inux.com,
	Liam Girdwood <lgirdwood@...il.com>,
	Heiko Stübner <heiko@...ech.de>
Subject: Re: [PATCH v2 0/9] regulator: pwm-regulator: Introduce
 continuous-mode

On Thu, 09 Jul 2015, Doug Anderson wrote:
> On Thu, Jul 9, 2015 at 6:14 AM, Boris Brezillon
> <boris.brezillon@...e-electrons.com> wrote:
> >> If you wish to add a 3rd mode, then I'm sure Mark will accept
> >> submissions, but I think what you are suggesting would be pretty
> >> complex and out-of-scope of what this patch-set is trying to achieve.
> >
> > Okay, still don't get the need to add a new mode which is almost doing
> > the same thing when we could have implemented it in a generic way in the
> > first place. But if your version has already been accepted then I think
> > I'll have to propose a new mode :-/.
> >
> >>
> >> As a side note, then if the voltage isn't directly proportional to the
> >> duty cycle on a large scale i.e. max => min, then it will not likely
> >> be very accurate between say table entries 1 => 2, or 4 => 5, etc.
> >>
> >> What I suggest you do in your case is provide a larger table with all
> >> of the values you find interesting, as it sounds like your PWM
> >> regulator isn't doing what one would normally expect.
> >
> > Well, I do not exactly agree here. Yes if you want to have a precise
> > mapping you'll have to add more entries in your voltage table, but
> > using linear interpolation between two points can be precise enough on
> > some ranges and prevent one to define a complete voltage table in the
> > DT.
> >
> > Doug, could give more details about the regulator used on the veyron
> > board ?
> 
> There's no need for a new mode as far as veyron is concerned.  The pwm
> regulator on veyron (as far as I understand it) acts the way that Lee
> describes.  Try doing the math on the values in the table and you
> should see that it's as linear as it can be while still using integral
> duty cycles.
> 
> Originally I only suggested using "linear interpolation" because:
> 
> * It meant no bindings change, which is always nice to avoid.
> 
> * It meant that old devices got this new mode, which is probably the
> right thing anyway (I think).  Maybe nobody has published DTS files
> with pwm-regulator, so the point is moot.

Great news.  This means that you provide the voltage the regulator
will provide with 0% duty cycle and 100% duty cycle and you're hot to
trot.  No further configuration/bindings required.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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