linux-kernel - Re: [PATCH 2/4] pwm: pca9685: remove ALL

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Message-ID: <20200330154036.GB2817345@ulmo>
Date:   Mon, 30 Mar 2020 17:40:36 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     Matthias Schiffer <matthias.schiffer@...tq-group.com>,
        u.kleine-koenig@...gutronix.de, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, andy.shevchenko@...il.com
Subject: Re: [PATCH 2/4] pwm: pca9685: remove ALL_LED PWM channel

On Mon, Mar 30, 2020 at 03:34:50PM +0200, Clemens Gruber wrote:
> Hi,
> 
> On Mon, Mar 30, 2020 at 03:07:57PM +0200, Thierry Reding wrote:
> > On Wed, Feb 26, 2020 at 02:52:27PM +0100, Matthias Schiffer wrote:
> > > The interaction of the ALL_LED PWM channel with the other channels was
> > > not well-defined. As the ALL_LED feature does not seem very useful and
> > > it was making the code significantly more complex, simply remove it.
> > > 
> > > Signed-off-by: Matthias Schiffer <matthias.schiffer@...tq-group.com>
> > > ---
> > >  drivers/pwm/pwm-pca9685.c | 115 ++++++--------------------------------
> > >  1 file changed, 17 insertions(+), 98 deletions(-)
> > 
> > Applied, thanks.
> > 
> > Thierry
> 
> I was not reading the mailing list in the last weeks, so I only saw the
> patch today.
> 
> We are using the ALL_LED channel in production to reduce the delay when
> all 16 PWM outputs need to be set to the same duty cycle.
> 
> I am not sure it is a good idea to remove this feature.

Can you specify what platform this is and where the code is that does
this. I can't really find any device tree users of this and I don't know
if there's a good way to find out what other users there are, but this
isn't the first time this driver has created confusion, so please help
collect some more information about it's use so we can avoid this in the
future.

I'll back out this particular patch since you're using it. Can you give
the other three patches a try to see if they work for you?

Thierry

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