Re: [PATCH 3/4] pwm: pca9685: initialize all LED registers during probe

Uwe Kleine-König
2020-02-26T15:01:00Z

On Wed, Feb 26, 2020 at 02:52:28PM +0100, Matthias Schiffer wrote:
> Initialize all ON delays to 0 during probe, rather than doing it in
> pca9685_pwm_enable.
>
> Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> ---
> drivers/pwm/pwm-pca9685.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 393ab92aa945..370691b21107 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -289,13 +289,6 @@ static int pca9685_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
> {
> struct pca9685 *pca = to_pca(chip);
>
> - /*
> - * The PWM subsystem does not support a pre-delay.
> - * So, set the ON-timeout to 0
> - */
> - regmap_write(pca->regmap, LED_N_ON_L(pwm->hwpwm), 0);
> - regmap_write(pca->regmap, LED_N_ON_H(pwm->hwpwm), 0);
> -
> /*
> * Clear the full-off bit.
> * It has precedence over the others and must be off.
> @@ -388,6 +381,13 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, 0);
>
> + /*
> + * The PWM subsystem does not support a pre-delay.
> + * So, set the ON-timeout to 0
> + */
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> +

What is a pre-delay: Something like:
_________ ______
_____/ \_________________/
^ ^

Where ^ marks the period start and then the time between period start
and the rising signal is the pre-delay?

If so, the IMHO more right approach is to keep the pre-delay until a new
setting is applied and in .get_state ignore the pre-delay. This way you
don't modify the output in .probe() which sounds right.

Best regards
Uwe

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