linux-kernel - Re: [PATCH 1/2] pwm: pca9685: fix period change with same duty cycle

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Message-ID: <20170118110948.GN2023@lahna.fi.intel.com>
Date:   Wed, 18 Jan 2017 13:09:48 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Clemens Gruber <clemens.gruber@...ruber.com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stable@...r.kernel.org,
        Florian Vaussard <florian.vaussard@...g-vd.ch>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH 1/2] pwm: pca9685: fix period change with same duty cycle

On Wed, Jan 18, 2017 at 11:56:50AM +0100, Thierry Reding wrote:
> On Tue, Dec 13, 2016 at 04:52:50PM +0100, Clemens Gruber wrote:
> > When first implementing support for changing the output frequency, an
> > optimization was added to continue the PWM after changing the prescaler
> > without having to reprogram the ON and OFF registers for the duty cycle,
> > in case the duty cycle stayed the same.
> > This was flawed, because we compared the absolute value of the duty
> > cycle in nanoseconds instead of the ratio to the period.
> > 
> > Fix the problem by removing the shortcut.
> > 
> > Fixes: 01ec8472009c9 ("pwm-pca9685: Support changing the output frequency")
> > Cc: <stable@...r.kernel.org> # v4.3+
> > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> > ---
> >  drivers/pwm/pwm-pca9685.c | 11 -----------
> >  1 file changed, 11 deletions(-)
> 
> Mika, Andy, can you guys help review this and 2/2?

Looks good to me.

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>