On Tue, Apr 06, 2021 at 06:41:34PM +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 <clemens.gruber@xxxxxxxxxxxx>
> ---
> Changes since v6:
> - Added a comment regarding the division (Suggested by Uwe)
> - Rebased
>
> drivers/pwm/pwm-pca9685.c | 46 +++++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 5a2ce97e71fd..d4474c5ff96f 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -333,6 +333,51 @@ 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);
> + /*
> + * PCA9685_OSC_CLOCK_MHZ is 25, i.e. an integer divider of 1000.
> + * The following calculation is therefore only a multiplication
> + * and we are not losing precision.
> + */
> + 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;
Given that with duty = 0 the chip is still "on" and changing the duty
will first complete the currently running period, I'd model duty=0 as
enabled. This also simplifies the code a bit, to something like:
state->enabled = true;
duty = pca9685_pwm_get_duty(pca, pwm->hwpwm);
state->duty_cycle = div_round_up(duty * state->period, PCA9685_COUNTER_RANGE);
(I'm using round-up here assuming apply uses round-down to get
idempotency. In the current patch set state this is wrong however.)
> +}
> +
> static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
> {
> struct pca9685 *pca = to_pca(chip);
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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