linux-kernel - Re: [PATCH v2 00/11] pwm: Add support for PWM Capture

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Date:	Mon, 6 Jun 2016 20:46:03 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org, kernel@...inux.com,
	ajitpal.singh@...com, thierry.reding@...il.com,
	maxime.coquelin@...com
Subject: Re: [PATCH v2 00/11] pwm: Add support for PWM Capture

On Mon, 6 Jun 2016 16:32:31 +0100
Lee Jones <lee.jones@...aro.org> wrote:

> On Fri, 29 Apr 2016, Boris Brezillon wrote:
> 
> > Hi Lee,
> > 
> > On Fri, 22 Apr 2016 11:18:04 +0100
> > Lee Jones <lee.jones@...aro.org> wrote:
> >   
> > > The first part of this set extends the current PWM API to allow external
> > > code to request a PWM Capture.  Subsequent patches then make use of the
> > > new API by providing a userspace offering via /sysfs.  The final part of
> > > the set supplies PWM Capture functionality into the already existing STi
> > > PWM driver.  
> > 
> > Is there a reason you decided to not put this driver in IIO? IMHO, it
> > would be more appropriate to make your PWM device an MFD that can either
> > bind to the PWM or the capture driver.
> > And BTW, IIO already has a sysfs interface (you may have to extend the
> > API to support your type of capture though).  
> 
> Multi-Function Device drivers can only be justified if the IP
> contained does not and can not live in a single subsystem.  The IP
> which controls both PWM-in and PWM-out in this device is the same.  I
> can't fathom a sane reason why you would wish to separate this
> functionality over multiple subsystems.
> 

Well, I still think what you describe as PWM-in is actually a capture
device that would perfectly fit in the IIO subsystem, and I guess you
can't use the PWM IP as a capture and waveform generator device as the
same time, which is why I suggested the MFD approach to select the mode.

Anyway, I'm not the PWM or the IIO maintainer, so I'm just sharing my
opinion here.

Regards,

Boris

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com