On Mon, Mar 29, 2021 at 02:57:02PM +0200, Clemens Gruber wrote: > Implements .get_state to read-out the current hardware state. > > The hardware readout may return slightly different values than those > that were set in apply due to the limited range of possible prescale and > counter register values. > > Also note that although the datasheet mentions 200 Hz as default > frequency when using the internal 25 MHz oscillator, the calculated > period from the default prescaler register setting of 30 is 5079040ns. > > Signed-off-by: Clemens Gruber <[email protected]> > --- > drivers/pwm/pwm-pca9685.c | 41 +++++++++++++++++++++++++++++++++++++++ > 1 file changed, 41 insertions(+) > > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c > index 0ed1013737e3..fb026a25fb61 100644 > --- a/drivers/pwm/pwm-pca9685.c > +++ b/drivers/pwm/pwm-pca9685.c > @@ -333,6 +333,46 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, > struct pwm_device *pwm, > return 0; > } > > +static void pca9685_pwm_get_state(struct pwm_chip *chip, struct pwm_device > *pwm, > + struct pwm_state *state) > +{ > + struct pca9685 *pca = to_pca(chip); > + unsigned long long duty; > + unsigned int val = 0; > + > + /* Calculate (chip-wide) period from prescale value */ > + regmap_read(pca->regmap, PCA9685_PRESCALE, &val); > + state->period = (PCA9685_COUNTER_RANGE * 1000 / PCA9685_OSC_CLOCK_MHZ) * > + (val + 1);
As we have PCA9685_OSC_CLOCK_MHZ = 25 this is an integer calculation
without loss of precision. It might be worth to point that out in a
comment. (Otherwise doing the division at the end might be more
sensible.)
> + /* The (per-channel) polarity is fixed */
> + state->polarity = PWM_POLARITY_NORMAL;
> +
> + if (pwm->hwpwm >= PCA9685_MAXCHAN) {
> + /*
> + * The "all LEDs" channel does not support HW readout
> + * Return 0 and disabled for backwards compatibility
> + */
> + state->duty_cycle = 0;
> + state->enabled = false;
> + return;
> + }
> +
> + duty = pca9685_pwm_get_duty(pca, pwm->hwpwm);
> +
> + state->enabled = !!duty;
> + if (!state->enabled) {
> + state->duty_cycle = 0;
> + return;
> + } else if (duty == PCA9685_COUNTER_RANGE) {
> + state->duty_cycle = state->period;
> + return;
> + }
> +
> + duty *= state->period;
> + state->duty_cycle = duty / PCA9685_COUNTER_RANGE;
.apply uses ROUND_CLOSEST to calculate duty from state->duty_cycle,
still using / here (instead of ROUND_CLOSEST), but again as
PCA9685_OSC_CLOCK_MHZ is 25 this calculation doesn't suffer from
rounding errors. So if you feed the state returned here into .apply
again, there is (as I want it) no change.
The only annoyance is that if PCA9685_PRESCALE holds a value smaller
than 3, .apply() will fail. Not sure there is any saner way to handle
this.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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