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

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Date:	Thu, 9 Jul 2015 16:44:30 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	broonie@...nel.org, kernel@...inux.com, lgirdwood@...il.com,
	Doug Anderson <dianders@...gle.com>
Subject: Re: [PATCH v2 0/9] regulator: pwm-regulator: Introduce
 continuous-mode

> > > Lee Jones <lee.jones@...aro.org> wrote:
> > > 
> > > > This patch-set has been rebased on to topic/pwm.
> > > >   
> > > > Continuous mode uses the PWM regulator's maximum and minimum supplied
> > > > voltages specified in the regulator-{min,max}-microvolt properties to
> > > > calculate appropriate duty-cycle values.  This allows for a much more
> > > > fine grained solution when compared with voltage-table mode, which
> > > > this driver already supports.  This solution does make an assumption
> > > > that a %50 duty-cycle value will cause the regulator voltage to run
> > > > at half way between the supplied max_uV and min_uV values.
> > > 
> > > Well, I'm not sure this assumption works for all pwm driven regulators.
> > > What if your regulator does not react linearly to the PWM duty-cycle
> > > config ?
> > > 
> > > How about addressing that by using all the entries of the
> > > voltage<->duty table association and doing the linear interpolation
> > > between the provided points instead of doing it on the min -> max
> > > range ?
> > 
> > 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 :-/.

This solution is very generic.  What you're suggesting is pretty
non-standard I think.  This solution specifically doesn't account for
wonky/non-linear PWM regulators -- that's why I made the effort to
write it as an explicit assumption.

FYI, I just sent a patch amending the binding documentation.  It
should prevent any further confusion.

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