Re: [PATCH v2 4/7] pwm: Add support for Azoteq IQS620A PWM generator

From: Jeff LaBundy <jeff@labundy.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	"lars@metafoo.de" <lars@metafoo.de>,
	"pmeerw@pmeerw.net" <pmeerw@pmeerw.net>,
	"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"dmitry.torokhov@gmail.com" <dmitry.torokhov@gmail.com>,
	"robh+dt@kernel.org" <robh+dt@kernel.org>,
	"thierry.reding@gmail.com" <thierry.reding@gmail.com>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
	"lee.jones@linaro.org" <lee.jones@linaro.org>,
	"jic23@kernel.org" <jic23@kernel.org>,
	"knaack.h@gmx.de" <knaack.h@gmx.de>
Subject: Re: [PATCH v2 4/7] pwm: Add support for Azoteq IQS620A PWM generator
Date: Fri, 10 Jan 2020 04:29:08 +0000	[thread overview]
Message-ID: <20200110042851.GA23906@labundy.com> (raw)
In-Reply-To: <20200107111940.ymiey7npx6rrppqz@pengutronix.de>

Hi Uwe,

On Tue, Jan 07, 2020 at 12:19:40PM +0100, Uwe Kleine-König wrote:
> Hi Jeff,
> 
> On Wed, Jan 01, 2020 at 10:39:36PM +0000, Jeff LaBundy wrote:
> > On Sun, Dec 22, 2019 at 10:48:51PM +0100, Uwe Kleine-König wrote:
> > > On Sat, Dec 21, 2019 at 03:28:01AM +0000, Jeff LaBundy wrote:
> > > > Based on your other feedback, I'm moving forward under the impression that
> > > > you'll still accept option (2); please let me know if I have misunderstood
> > > > (thank you for being flexible).
> > > 
> > > Yeah, that's fine. If in the end it shows that this is a bad idea we can
> > > still change to (3).
> > 
> > Sounds great. As soon as 5.5-rc5 lands this weekend, I'll rebase v3 and
> > send it out.
> > 
> > I failed to catch this in my previous reply, but the comment I've added
> > to iqs620_pwm_get_state actually reads as follows:
> > 
> > /*
> >  * Since the device cannot generate a 0% duty cycle, requests to do so
> >  * force subsequent calls to iqs620_pwm_get_state to report the output
> >  * as disabled with duty cycle equal to that which was in use prior to
> >  * the request. This is not ideal, but is the best compromise based on
> >  * the capabilities of the device.
> >  */
> > 
> > This matches the present implementation, not your proposed comment that
> > claims duty cycle is clamped to 1 / 256 ms following a request for a 0%
> > duty cycle.
> 
> Yeah, if that's the mechanism that is actually implemented, that's fine
> of course.
> 
> > This seems OK since the concept of a duty cycle or period aren't really
> > relevant if the output is disabled in my opinion. However if you prefer
> > I update iqs620_pwm_apply to clamp duty cycle to 1 / 256 ms (instead of
> > leaving it untouched) in this case, please let me know.
> 
> For a disabled PWM the duty_cycle and period are not relevant, for an
> enabled PWM running with 0% the period matters (at least in theory)
> however.
> 

Agreed in full. We should be covered here since we report the (fixed)
period in all cases.

> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |

I managed to send out v3 this past weekend; please let me know if you
have any further feedback or you find it to be satisfactory.

Kind regards,
Jeff LaBundy