Hello Clemens,
On Mon, Mar 29, 2021 at 07:33:56PM +0200, Clemens Gruber wrote:
> On Mon, Mar 29, 2021 at 07:15:59PM +0200, Uwe Kleine-König wrote:
> > On Mon, Mar 29, 2021 at 02:57:06PM +0200, Clemens Gruber wrote:
> > > @@ -330,14 +345,22 @@ static int pca9685_pwm_apply(struct pwm_chip *chip,
> > > struct pwm_device *pwm,
> > >
> > > if (!state->enabled || duty < 1) {
> > > pca9685_pwm_set_duty(pca, pwm->hwpwm, 0);
> > > + clear_bit(pwm->hwpwm, pca->prescaler_users);
> >
> > Hmm, so if "my" channel runs at say
> >
> > .duty_cycle = 2539520 ns
> > .period = 5079040 ns
> >
> > and I call pwm_apply_state(mypwm, { .duty_cycle = 0, .period = 5079040,
> > enabled = true }); it might happen that another channel modifies the
> > period and I won't be able to return to the initial setting.
>
> Yes, that's correct.
>
> But that also applies to PWMs set to 100%:
>
> pwm_apply_state(mypwm, { .duty_cycle = 5079040, .period = 5079040,
> enabled = true });
>
> As this sets the full ON bit and does not use the prescaler, with the
> current code, another channel could modify the period and you wouldn't
> be able to return to the initial setting of 50%.
>
> > So I think it's sensible to only clear the user bit if the PWM is
> > disabled, but not if it is configured for duty_cycle = 0.
> >
> > Does this make sense?
>
> With both cases in mind, you are suggesting we block modifications of
> the prescaler if other PWMs are enabled and not if other PWMs are using
> the prescaler?That sounds sensible, yes. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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