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

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Date:   Wed, 16 Dec 2020 23:02:03 -0500
From:   Sven Van Asbroeck <thesven73@...il.com>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>, Lee Jones <lee.jones@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        David Jander <david@...tonic.nl>
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
<clemens.gruber@...ruber.com> 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 <clemens.gruber@...ruber.com>
> ---
>  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
>