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

Clemens Gruber
2020-11-15T17:46:07Z

On Thu, Nov 12, 2020 at 05:37:50PM +0100, Clemens Gruber wrote:
> 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
>

Please ignore the whole series (we found a flaw!).

Will send a v2 in the upcoming week.

Best regards,
Clemens