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References: <20201207193629.493241-1-clemens.gruber@pqgruber.com> <20201207220025.42b6g76wq7ph5nvb@pengutronix.de>
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From:   Sven Van Asbroeck <thesven73@gmail.com>
Date:   Mon, 7 Dec 2020 17:34:58 -0500
Message-ID: <CAGngYiW6_T8GjLvHrzNk+nUN5L81BwivBTRQ4GofF8LOf1qexA@mail.gmail.com>
Subject: Re: [PATCH v4 1/4] pwm: pca9685: Switch to atomic API
To:     =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>
Cc:     Clemens Gruber <clemens.gruber@pqgruber.com>,
        linux-pwm@vger.kernel.org,
        Thierry Reding <thierry.reding@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        David Jander <david@protonic.nl>
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Hi Uwe,

On Mon, Dec 7, 2020 at 5:00 PM Uwe Kleine-K=C3=B6nig
<u.kleine-koenig@pengutronix.de> wrote:
>
> This is not acceptable, if you have two PWM outputs and a consumer
> modifies one of them the other must change. So if this chip only
> supports a single period length of all channels, the first consumer
> enabling a channel defines the period to be used. All later consumers
> must live with that. (Also the first must be denied modifying the period
> if a second consumer has enabled its PWM.)

That makes sense. However, a possible wrinkle: when more than one pwm chann=
el
is requested, which one is able to change the period?

Example:
1. start with all pwms free
2. pwm_request(0), pwm_apply(period=3D200Hz)
3. pwm_request(1)
4. pwm_apply(1, period=3D400Hz) fails?
5. pwm_apply(0, period=3D400Hz) succeeds?

And if (5) succeeds, then pwm_get_state(1) will still return period=3D200Hz=
,
because the pwm core doesn't realize anything has changed. Are you ok
with this behaviour?