On Tue, Nov 24, 2020 at 1:10 PM Clemens Gruber
<clemens.gru...@pqgruber.com> wrote:
>
> The PCA9685 supports staggered LED output ON times to minimize current
> surges and reduce EMI.
> When this new option is enabled, the ON times of each channel are
> delayed by channel number x counter range / 16, which avoids asserting
> all enabled outputs at the same counter value while still maintaining
> the configured duty cycle of each output.
>
> Signed-off-by: Clemens Gruber <clemens.gru...@pqgruber.com>
> ---
>
> Changes since v1:
> - Rebased
>
> drivers/pwm/pwm-pca9685.c | 35 ++++++++++++++++++++++++++++++++++-
> 1 file changed, 34 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 2b82b35ff0de..37c80bc8edcf 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -75,6 +75,7 @@ struct pca9685 {
> struct pwm_chip chip;
> struct regmap *regmap;
> int prescale;
> + bool staggered_outputs;
> #if IS_ENABLED(CONFIG_GPIOLIB)
> struct mutex lock;
> struct gpio_chip gpio;
> @@ -329,7 +330,7 @@ static int pca9685_pwm_apply(struct pwm_chip *chip,
> struct pwm_device *pwm,
> {
> struct pca9685 *pca = to_pca(chip);
> unsigned long long duty, prescale;
> - unsigned int reg;
> + unsigned int on, off, reg;
>
> if (state->polarity != PWM_POLARITY_NORMAL)
> return -EOPNOTSUPP;
> @@ -375,6 +376,32 @@ static int pca9685_pwm_apply(struct pwm_chip *chip,
> struct pwm_device *pwm,
> duty = (PCA9685_COUNTER_RANGE - 1) * state->duty_cycle;
> duty = DIV_ROUND_UP_ULL(duty, state->period);
>
> + if (pca->staggered_outputs) {
> + if (pwm->hwpwm < PCA9685_MAXCHAN) {
> + /*
> + * To reduce EMI, the ON times of each channel are
> + * spread out evenly within the counter range, while
> + * still maintaining the configured duty cycle
> + */
> + on = pwm->hwpwm * PCA9685_COUNTER_RANGE /
> + PCA9685_MAXCHAN;
> + off = (on + duty) % PCA9685_COUNTER_RANGE;
Will pwm_get_state() still return the correct duty cycle in case
of staggered outputs?
> + regmap_write(pca->regmap, LED_N_ON_L(pwm->hwpwm),
> + on & 0xff);
> + regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm),
> + (on >> 8) & 0xf);
> + regmap_write(pca->regmap, LED_N_OFF_L(pwm->hwpwm),
> + off & 0xff);
> + regmap_write(pca->regmap, LED_N_OFF_H(pwm->hwpwm),
> + (off >> 8) & 0xf);
> + return 0;
> + }
> +
> + /* No staggering possible if "all LEDs" channel is used */
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> + }
> +
> if (pwm->hwpwm >= PCA9685_MAXCHAN)
> reg = PCA9685_ALL_LED_OFF_L;
> else
> @@ -470,6 +497,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>
> regmap_write(pca->regmap, PCA9685_MODE2, reg);
>
> + pca->staggered_outputs = device_property_read_bool(
> + &client->dev, "staggered-outputs");
> +
> /* Disable all LED ALLCALL and SUBx addresses to avoid bus collisions
> */
> regmap_read(pca->regmap, PCA9685_MODE1, ®);
> reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
> @@ -478,6 +508,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> /* Reset OFF registers to HW default (only full OFF bit is set) */
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> + /* Reset ON registers to HW default */
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
>
> pca->chip.ops = &pca9685_pwm_ops;
> /* Add an extra channel for ALL_LED */
> --
> 2.29.2
>
