[PATCH 1/2] pwm: pca9685: fix duty cycle loss on disable/enable

Clemens Gruber
2020-11-12T16:45:50Z

Currently, disabling a pwm channel clears the OFF registers, which
resets the configured duty cycle. Therefore, after a disable/enable
sequence, the pwm state is not in the same state as it was before.
As a workaround, the user had to do a config call after disable/enable.

Fix it by only toggling the "full-off" bit in disable/enable and no
longer use the "full-on" / "full-off" bits in config.

From now on, the "full-on" bit is only used in GPIO mode and the
"full-off" bit is only used in disable/enable, which also reduces
complexity in the driver.

Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.com>
---
drivers/pwm/pwm-pca9685.c | 83 +++++----------------------------------
1 file changed, 9 insertions(+), 74 deletions(-)

diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
index 4a55dc18656c..df214758256e 100644
--- a/drivers/pwm/pwm-pca9685.c
+++ b/drivers/pwm/pwm-pca9685.c
@@ -283,45 +283,7 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
}
}

- if (duty_ns < 1) {
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_OFF_H;
- else
- reg = LED_N_OFF_H(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, LED_FULL);
-
- return 0;
- }
-
- if (duty_ns == period_ns) {
- /* Clear both OFF registers */
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_OFF_L;
- else
- reg = LED_N_OFF_L(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0x0);
-
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_OFF_H;
- else
- reg = LED_N_OFF_H(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0x0);
-
- /* Set the full ON bit */
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_ON_H;
- else
- reg = LED_N_ON_H(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, LED_FULL);
-
- return 0;
- }
-
- duty = PCA9685_COUNTER_RANGE * (unsigned long long)duty_ns;
+ duty = (PCA9685_COUNTER_RANGE - 1) * (unsigned long long)duty_ns;
duty = DIV_ROUND_UP_ULL(duty, period_ns);

if (pwm->hwpwm >= PCA9685_MAXCHAN)
@@ -338,14 +300,6 @@ static int pca9685_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,

regmap_write(pca->regmap, reg, ((int)duty >> 8) & 0xf);

- /* Clear the full ON bit, otherwise the set OFF time has no effect */
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_ON_H;
- else
- reg = LED_N_ON_H(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0);
-
return 0;
}

@@ -354,24 +308,6 @@ static int pca9685_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
struct pca9685 *pca = to_pca(chip);
unsigned int reg;

- /*
- * The PWM subsystem does not support a pre-delay.
- * So, set the ON-timeout to 0
- */
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_ON_L;
- else
- reg = LED_N_ON_L(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0);
-
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_ON_H;
- else
- reg = LED_N_ON_H(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0);
-
/*
* Clear the full-off bit.
* It has precedence over the others and must be off.
@@ -391,20 +327,16 @@ static void pca9685_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
struct pca9685 *pca = to_pca(chip);
unsigned int reg;

+ /*
+ * Set the full-off bit.
+ * It has precedence over the others.
+ */
if (pwm->hwpwm >= PCA9685_MAXCHAN)
reg = PCA9685_ALL_LED_OFF_H;
else
reg = LED_N_OFF_H(pwm->hwpwm);

- regmap_write(pca->regmap, reg, LED_FULL);
-
- /* Clear the LED_OFF counter. */
- if (pwm->hwpwm >= PCA9685_MAXCHAN)
- reg = PCA9685_ALL_LED_OFF_L;
- else
- reg = LED_N_OFF_L(pwm->hwpwm);
-
- regmap_write(pca->regmap, reg, 0x0);
+ regmap_update_bits(pca->regmap, reg, LED_FULL, LED_FULL);
}

static int pca9685_pwm_request(struct pwm_chip *chip, struct pwm_device *pwm)
@@ -487,6 +419,9 @@ static int pca9685_pwm_probe(struct i2c_client *client,
/* Clear all "full off" bits */
regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, 0);
+ /* Clear all "on" regs */
+ 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