linux-kernel - Re: [PATCH v3 4/5] pwm: omap-dmtimer: Do not disable pwm before changing period/duty

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Date:   Thu, 12 Mar 2020 07:21:26 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Lokesh Vutla <lokeshvutla@...com>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Thierry Reding <thierry.reding@...il.com>,
        Tony Lindgren <tony@...mide.com>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        Sekhar Nori <nsekhar@...com>, Vignesh R <vigneshr@...com>,
        kernel@...gutronix.de
Subject: Re: [PATCH v3 4/5] pwm: omap-dmtimer: Do not disable pwm before
 changing period/duty_cycle

On Thu, Mar 12, 2020 at 04:14:34PM +0530, Lokesh Vutla wrote:
> But the problem here is that inactive breaks between two periods is not desired.
> Because the pwm is used to generate a 1PPS signal and is continuously
> synchronized with PTP clock.

The 1-PPS case is the "easy" one.  If the PWM is adjustable on the
fly, then people will use it with higher frequency signals.
 
> I am up if this can be solved generically. But updating period is very specific
> to hardware implementation. Not sure what generic solution can be brought out of
> this. Please correct me if I am wrong.

What happens today when the PWM frequency or duty cycle are changed
while the signal is enabled?

Do different PWM devices/drivers behave the same way?

Does this series change the behavior of the am335x and friends?

Thanks,
Richard