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

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Message-ID: <20200226151034.7i3h5blmrwre2yzg@pengutronix.de>
Date:   Wed, 26 Feb 2020 16:10:34 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     thierry.reding@...il.com, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] pwm: pca9685: remove unused duty_cycle struct element

Hello Matthias,

as you seem to have this hardware on your desk, it would be great if you
could answer the following questions:

 - Does the hardware complete the currently running period before
   applying a new setting?
 - Is this racy somehow (i.e. can it happen that when going from
   duty_cycle/period = 1000/5000 to duty_cycle/period = 4000/10000 the
   output is 1000/10000 (or 4000/5000) for one cycle)?
 - Does the hardware complete the currently running period before
   .enabled = false is configured?
 - How does the output pin behave on a disabled PWM. (Usual candidates
   are: freeze where is just happens to be, constant inactive and
   High-Z).

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |