The PCA9685 supports staggered LED output ON times to minimize current
surges and reduce EMI.
When the PWM_STAGGERING_ALLOWED flag is set for a channel, its ON time
is delayed by channel number x counter range / 16, which avoids
asserting all the 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 v6:
- Use a per-PWM flag instead of one global DT parameter
drivers/pwm/pwm-pca9685.c | 60 ++++++++++++++++++++++++++++++---------
1 file changed, 46 insertions(+), 14 deletions(-)
diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 0bcec04b138a..24221ee7a77a 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -93,46 +93,73 @@ static inline struct pca9685 *to_pca(struct pwm_chip *chip)
/* Helper function to set the duty cycle ratio to duty/4096 (e.g. duty=2048 ->
50%) */
static void pca9685_pwm_set_duty(struct pca9685 *pca, int channel, unsigned
int duty)
{
+ struct pwm_device *pwm = &pca->chip.pwms[channel];
+ unsigned int on, off;
+
if (duty == 0) {
/* Set the full OFF bit, which has the highest precedence */
regmap_write(pca->regmap, REG_OFF_H(channel), LED_FULL);
+ return;
} else if (duty >= PCA9685_COUNTER_RANGE) {
/* Set the full ON bit and clear the full OFF bit */
regmap_write(pca->regmap, REG_ON_H(channel), LED_FULL);
regmap_write(pca->regmap, REG_OFF_H(channel), 0);
- } else {
- /* Set OFF time (clears the full OFF bit) */
- regmap_write(pca->regmap, REG_OFF_L(channel), duty & 0xff);
- regmap_write(pca->regmap, REG_OFF_H(channel), (duty >> 8) &
0xf);
- /* Clear the full ON bit */
- regmap_write(pca->regmap, REG_ON_H(channel), 0);
+ return;
}
+
+
+ if (pwm->args.staggering_allowed && channel < 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 = channel * PCA9685_COUNTER_RANGE / PCA9685_MAXCHAN;
+ } else
+ on = 0;
+
+ off = (on + duty) % PCA9685_COUNTER_RANGE;
+
+ /* Set ON time (clears full ON bit) */
+ regmap_write(pca->regmap, REG_ON_L(channel), on & 0xff);
+ regmap_write(pca->regmap, REG_ON_H(channel), (on >> 8) & 0xf);
+ /* Set OFF time (clears full OFF bit) */
+ regmap_write(pca->regmap, REG_OFF_L(channel), off & 0xff);
+ regmap_write(pca->regmap, REG_OFF_H(channel), (off >> 8) & 0xf);
}
static unsigned int pca9685_pwm_get_duty(struct pca9685 *pca, int channel)
{
- unsigned int off_h = 0, val = 0;
+ struct pwm_device *pwm = &pca->chip.pwms[channel];
+ unsigned int off = 0, on = 0, val = 0;
if (WARN_ON(channel >= PCA9685_MAXCHAN)) {
/* HW does not support reading state of "all LEDs" channel */
return 0;
}
- regmap_read(pca->regmap, LED_N_OFF_H(channel), &off_h);
- if (off_h & LED_FULL) {
+ regmap_read(pca->regmap, LED_N_OFF_H(channel), &off);
+ if (off & LED_FULL) {
/* Full OFF bit is set */
return 0;
}
- regmap_read(pca->regmap, LED_N_ON_H(channel), &val);
- if (val & LED_FULL) {
+ regmap_read(pca->regmap, LED_N_ON_H(channel), &on);
+ if (on & LED_FULL) {
/* Full ON bit is set */
return PCA9685_COUNTER_RANGE;
}
- val = 0;
regmap_read(pca->regmap, LED_N_OFF_L(channel), &val);
- return ((off_h & 0xf) << 8) | (val & 0xff);
+ off = ((off & 0xf) << 8) | (val & 0xff);
+ if (!pwm->args.staggering_allowed)
+ return off;
+
+ /* Read ON register to calculate duty cycle of staggered output */
+ val = 0;
+ regmap_read(pca->regmap, LED_N_ON_L(channel), &val);
+ on = ((on & 0xf) << 8) | (val & 0xff);
+ return (off - on) & (PCA9685_COUNTER_RANGE - 1);
}
#if IS_ENABLED(CONFIG_GPIOLIB)
@@ -453,9 +480,11 @@ static int pca9685_pwm_probe(struct i2c_client *client,
reg &= ~(MODE1_ALLCALL | MODE1_SUB1 | MODE1_SUB2 | MODE1_SUB3);
regmap_write(pca->regmap, PCA9685_MODE1, reg);
- /* Reset OFF registers to POR default */
+ /* Reset OFF/ON registers to POR default */
regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, LED_FULL);
regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
+ 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 */
@@ -464,6 +493,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
pca->chip.dev = &client->dev;
pca->chip.base = -1;
+ pca->chip.of_xlate = of_pwm_xlate_with_flags;
+ pca->chip.of_pwm_n_cells = 3;
+
ret = pwmchip_add(&pca->chip);
if (ret < 0)
return ret;
--
2.31.1
