Messages in this thread | | | From | Sven Van Asbroeck <> | Date | Mon, 7 Dec 2020 17:34:58 -0500 | Subject | Re: [PATCH v4 1/4] pwm: pca9685: Switch to atomic API |
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Hi Uwe,
On Mon, Dec 7, 2020 at 5:00 PM Uwe Kleine-König <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 channel is requested, which one is able to change the period?
Example: 1. start with all pwms free 2. pwm_request(0), pwm_apply(period=200Hz) 3. pwm_request(1) 4. pwm_apply(1, period=400Hz) fails? 5. pwm_apply(0, period=400Hz) succeeds?
And if (5) succeeds, then pwm_get_state(1) will still return period=200Hz, because the pwm core doesn't realize anything has changed. Are you ok with this behaviour?
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