Re: [PATCH 6/6] hwmon: pwm-fan: Update the duty cycle inorder to control the pwm-fan

From: Guenter Roeck <linux@roeck-us.net>
To: Ben Gamari <ben@smart-cactus.org>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Sjoerd Simons <sjoerd.simons@collabora.co.uk>,
	Anand Moon <linux.amoon@gmail.com>,
	Lukasz Majewski <l.majewski@samsung.com>,
	Eduardo Valentin <edubezval@gmail.com>,
	Russell King <linux@arm.linux.org.uk>,
	Kukjin Kim <kgene@kernel.org>,
	devicetree@vger.kernel.org,
	"linux-samsung-soc@vger.kernel.org" 
	<linux-samsung-soc@vger.kernel.org>,
	linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Markus Reichl <m.reichl@fivetechno.de>
Subject: Re: [PATCH 6/6] hwmon: pwm-fan: Update the duty cycle inorder to control the pwm-fan
Date: Fri, 10 Apr 2015 10:58:01 -0700	[thread overview]
Message-ID: <20150410175801.GA31499@roeck-us.net> (raw)
In-Reply-To: <87h9snvqsf.fsf@gmail.com>

On Fri, Apr 10, 2015 at 01:25:52PM -0400, Ben Gamari wrote:
> Thierry Reding <thierry.reding@gmail.com> writes:
> 
> > On Fri, Apr 10, 2015 at 03:30:01PM +0200, Sjoerd Simons wrote:
> >> 
> >> Yes/no/maybe :). Imho this is something to clarify in the pwm API
> >> documentation. As currently all it says is: 
> >>   "pwm_disable - stop a PWM output toggling", 
> >> 
> >> Which is what the exynos driver does. 
> >> 
> >> Thierry, could you clearify what the intention is here? I'm happy to
> >> prepare a pwm driver patch if needed to solve this?
> >
> > I think the safest thing to do is for users to do both. You call
> > pwm_config() with a zero duty cycle to make it clear what the status is
> > that you want. Then you call pwm_disable() to state that you don't need
> > the output signal anymore, so that any clocks needed by the PWM can be
> > stopped. Doing so gives the driver the most information and should make
> > the user more resilient against any possible quirks in drivers.
> >
> It would be great if the documentation were more clear on this matter
> regardless. This is something I can imagine having to spend substantial
> amounts of time Googling whereas a simple note in the documentation would
> have removed all ambiguity.
> 
Especially since, in this case, the output signal _is_ still needed.
It appears that pwm_disable() is only expected to stop the clock, not
the signal itself.

Guenter