linux-kernel - Re: [PATCH v3 4/7] pwm: ntxec: Add driver for PWM function in Netronix EC

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Date:   Sat, 3 Oct 2020 11:17:58 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Heiko Stuebner <heiko@...ech.de>,
        devicetree <devicetree@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        Daniel Palmer <daniel@...f.com>,
        Andreas Kemnade <andreas@...nade.info>,
        NXP Linux Team <linux-imx@....com>,
        linux-pwm@...r.kernel.org, Stephan Gerhold <stephan@...hold.net>,
        allen <allen.chen@....com.tw>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Lubomir Rintel <lkundrak@...sk>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Heiko Stuebner <heiko.stuebner@...obroma-systems.com>,
        Josua Mayer <josua.mayer@....eu>,
        Shawn Guo <shawnguo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v3 4/7] pwm: ntxec: Add driver for PWM function in
 Netronix EC

On Sat, Oct 3, 2020 at 2:36 AM Jonathan Neuschäfer
<j.neuschaefer@....net> wrote:
> On Mon, Sep 28, 2020 at 10:35:46AM +0200, Uwe Kleine-König wrote:
> > On Sun, Sep 27, 2020 at 11:10:44PM +0200, Jonathan Neuschäfer wrote:

...

> > You can even check this with an LED using something like:
> >
> >       pwm_apply(mypwm, {.enabled = true, .duty_cycle = $big, .period = $big});
> >       pwm_apply(mypwm, {.enabled = false, ... });
> >
> > . If the period is completed the LED is on for $big ns, if not the LED
> > is on for a timespan that is probably hardly noticable with the human
> > eye.
>
> The longest configurable period is about 8ms, so it's not long enough to
> see anything. However, after writing enable=0, it can take about a
> second for the PWM signal to turn off... this hardware is a bit weird.

Sounds like you have 1/128 divisor and off/on is done on lower
frequency. (We saw PWMs with an additional 7-bit counter, reminds me
Crystal Cove PMIC PWM).

-- 
With Best Regards,
Andy Shevchenko