linux-kernel - Re: [PATCH v6 4/7] pwm: pca9685: Support staggered output ON times

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Message-ID: <YGILdjZBCc2vVlRd@workstation.tuxnet>
Date:   Mon, 29 Mar 2021 19:16:38 +0200
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 4/7] pwm: pca9685: Support staggered output ON times

On Mon, Mar 29, 2021 at 07:03:57PM +0200, Uwe Kleine-König wrote:
> On Mon, Mar 29, 2021 at 02:57:04PM +0200, Clemens Gruber wrote:
> > The PCA9685 supports staggered LED output ON times to minimize current
> > surges and reduce EMI.
> > When this new option is enabled, the ON times of each channel are
> > delayed by channel number x counter range / 16, which avoids asserting
> > all enabled outputs at the same counter value while still maintaining
> > the configured duty cycle of each output.
> > 
> > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> 
> Is there a reason to not want this staggered output? If it never hurts I
> suggest to always stagger and drop the dt property.

There might be applications where you want multiple outputs to assert at
the same time / to be synchronized.
With staggered outputs mode always enabled, this would no longer be
possible as they are spread out according to their channel number.

Not sure how often that usecase is required, but just enforcing the
staggered mode by default sounds risky to me.

Thanks,
Clemens