On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber <clemens.gru...@pqgruber.com> wrote: > > Implements .get_state to read-out the current hardware state. >
I am not convinced that we actually need this. Looking at the pwm core, .get_state() is only called right after .request(), to initialize the cached value of the state. The core then uses the cached value throughout, it'll never read out the h/w again, until the next .request(). In our case, we know that the state right after request is always disabled, because: - we disable all pwm channels on probe (in PATCH v5 4/7) - .free() disables the pwm channel Conclusion: .get_state() will always return "pwm disabled", so why do we bother reading out the h/w? Of course, if we choose to leave the pwm enabled after .free(), then .get_state() can even be left out! Do we want that? Genuine question, I do not know the answer. > 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 <clemens.gru...@pqgruber.com> > --- > 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 1b5b5fb93b43..b3398963c0ff 100644 > --- a/drivers/pwm/pwm-pca9685.c > +++ b/drivers/pwm/pwm-pca9685.c > @@ -331,6 +331,46 @@ 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; > + > + /* 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); > + > + /* 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; > +} > + > static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm) > { > struct pca9685 *pca = to_pca(chip); > @@ -353,6 +393,7 @@ static void pca9685_pwm_free(struct pwm_chip *chip, > struct pwm_device *pwm) > > static const struct pwm_ops pca9685_pwm_ops = { > .apply = pca9685_pwm_apply, > + .get_state = pca9685_pwm_get_state, > .request = pca9685_pwm_request, > .free = pca9685_pwm_free, > .owner = THIS_MODULE, > -- > 2.29.2 >