linux-kernel - Re: (EXT) Re: [PATCH 1/4] pwm: pca9685: remove unused duty

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Message-ID: <CAGngYiUe-tihBJUcXQ738_5aA9pzgp_-NSs4iCrz3eWO6rMukA@mail.gmail.com>
Date:   Fri, 3 Apr 2020 19:50:07 -0400
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: (EXT) Re: [PATCH 1/4] pwm: pca9685: remove unused duty_cycle
 struct element

On Mon, Mar 30, 2020 at 11:12 AM Clemens Gruber
<clemens.gruber@...ruber.com> wrote:
>
> On Wed, Feb 26, 2020 at 06:03:02PM +0100, Matthias Schiffer wrote:
> > As it turns out, this driver is broken in yet another way I didn't find
> > before: For changing the global prescaler the chip needs to be put into
> > sleep mode, but the driver doesn't follow the restart sequence
> > described in the datasheet when waking it back up. In consequence,
> > changing the period of one PWM does not only modify the period of all
> > PWMs (which is bad enough, but can't be avoided with this hardware),
> > but it also leaves all PWMs disabled...
>
> I am unable to reproduce this: If I set a specific duty cycle on a
> channel and then change the period, the channel stays active.
> I can see the brightness of an LED decrease if I increase the period.

What happens when pwm channels 0 and 1 are both enabled, and
you change the pwm period of channel 0. Does channel 1 remain
on?