2020-12-17 04:04:18

by Sven Van Asbroeck

Subject: Re: [PATCH v5 4/7] pwm: pca9685: Reset registers to POR state in probe

Hi Clemens, minor nit below.

On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber
<[email protected]> wrote:
>
> Reset the prescale and ON/OFF registers to their POR default state in
> the probe function. Otherwise, the PWMs could still be active after a
> watchdog reset and reboot, etc.
>
> Signed-off-by: Clemens Gruber <[email protected]>
> ---
> drivers/pwm/pwm-pca9685.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index 7b14447f3c05..38aadaf50996 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -47,6 +47,7 @@
> #define PCA9685_ALL_LED_OFF_H 0xFD
> #define PCA9685_PRESCALE 0xFE
>
> +#define PCA9685_PRESCALE_DEF 0x1E /* => default frequency of ~200 Hz */
> #define PCA9685_PRESCALE_MIN 0x03 /* => max. frequency of 1526 Hz */
> #define PCA9685_PRESCALE_MAX 0xFF /* => min. frequency of 24 Hz */
>
> @@ -446,9 +447,11 @@ 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);
>
> - /* Clear all "full off" bits */
> + /* Reset ON/OFF registers to HW defaults (only full OFF bit is set) */
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
> - regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, 0);
> + regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
>
> pca->chip.ops = &pca9685_pwm_ops;
> /* Add an extra channel for ALL_LED */
> @@ -470,8 +473,10 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> /*
> * The chip comes out of power-up in the sleep state,
> * but force it to sleep in case it was woken up before
> + * and set the default prescale value
> */
> pca9685_set_sleep_mode(pca, true);
> + regmap_write(pca->regmap, PCA9685_PRESCALE, PCA9685_PRESCALE_DEF);
> pm_runtime_set_suspended(&client->dev);
> pm_runtime_enable(&client->dev);

Consider making it clearer that prescale can only be touched when the chip is
in sleep mode. Suggestion:

/* set the default prescale value - chip _must_ be in sleep mode */
regmap_write(pca->regmap, PCA9685_PRESCALE, PCA9685_PRESCALE_DEF);

>
> --
> 2.29.2
>

2020-12-17 17:48:11

by Clemens Gruber

Subject: Re: [PATCH v5 4/7] pwm: pca9685: Reset registers to POR state in probe

On Wed, Dec 16, 2020 at 11:02:03PM -0500, Sven Van Asbroeck wrote:
> Hi Clemens, minor nit below.
>
> On Wed, Dec 16, 2020 at 7:53 AM Clemens Gruber
> <[email protected]> wrote:
> >
> > Reset the prescale and ON/OFF registers to their POR default state in
> > the probe function. Otherwise, the PWMs could still be active after a
> > watchdog reset and reboot, etc.
> >
> > Signed-off-by: Clemens Gruber <[email protected]>
> > ---
> > drivers/pwm/pwm-pca9685.c | 9 +++++++--
> > 1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> > index 7b14447f3c05..38aadaf50996 100644
> > --- a/drivers/pwm/pwm-pca9685.c
> > +++ b/drivers/pwm/pwm-pca9685.c
> > @@ -47,6 +47,7 @@
> > #define PCA9685_ALL_LED_OFF_H 0xFD
> > #define PCA9685_PRESCALE 0xFE
> >
> > +#define PCA9685_PRESCALE_DEF 0x1E /* => default frequency of ~200 Hz */
> > #define PCA9685_PRESCALE_MIN 0x03 /* => max. frequency of 1526 Hz */
> > #define PCA9685_PRESCALE_MAX 0xFF /* => min. frequency of 24 Hz */
> >
> > @@ -446,9 +447,11 @@ 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);
> >
> > - /* Clear all "full off" bits */
> > + /* Reset ON/OFF registers to HW defaults (only full OFF bit is set) */
> > + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_L, 0);
> > + regmap_write(pca->regmap, PCA9685_ALL_LED_ON_H, 0);
> > regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_L, 0);
> > - regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, 0);
> > + regmap_write(pca->regmap, PCA9685_ALL_LED_OFF_H, LED_FULL);
> >
> > pca->chip.ops = &pca9685_pwm_ops;
> > /* Add an extra channel for ALL_LED */
> > @@ -470,8 +473,10 @@ static int pca9685_pwm_probe(struct i2c_client *client,
> > /*
> > * The chip comes out of power-up in the sleep state,
> > * but force it to sleep in case it was woken up before
> > + * and set the default prescale value
> > */
> > pca9685_set_sleep_mode(pca, true);
> > + regmap_write(pca->regmap, PCA9685_PRESCALE, PCA9685_PRESCALE_DEF);
> > pm_runtime_set_suspended(&client->dev);
> > pm_runtime_enable(&client->dev);
>
> Consider making it clearer that prescale can only be touched when the chip is
> in sleep mode. Suggestion:
>
> /* set the default prescale value - chip _must_ be in sleep mode */
> regmap_write(pca->regmap, PCA9685_PRESCALE, PCA9685_PRESCALE_DEF);

Good point, thanks.

>
> >
> > --
> > 2.29.2
> >