linux-kernel - Re: [PATCH v6 3/7] pwm: pca9685: Improve runtime PM behavior

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Date:   Mon, 29 Mar 2021 17:55:27 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 3/7] pwm: pca9685: Improve runtime PM behavior

On Mon, Mar 29, 2021 at 02:57:03PM +0200, Clemens Gruber wrote:
> The chip does not come out of POR in active state but in sleep state.
> To be sure (in case the bootloader woke it up) we force it to sleep in
> probe.
> 
> On kernels without CONFIG_PM, we wake the chip in .probe and put it to
> sleep in .remove.

What is the effect of sleep state? Does it continue to oscilate it the
bootloader set up some configuration?


> Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> ---
>  drivers/pwm/pwm-pca9685.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pwm/pwm-pca9685.c b/drivers/pwm/pwm-pca9685.c
> index fb026a25fb61..4d6684b90819 100644
> --- a/drivers/pwm/pwm-pca9685.c
> +++ b/drivers/pwm/pwm-pca9685.c
> @@ -469,14 +469,19 @@ static int pca9685_pwm_probe(struct i2c_client *client,
>  		return ret;
>  	}
>  
> -	/* The chip comes out of power-up in the active state */
> -	pm_runtime_set_active(&client->dev);
>  	/*
> -	 * Enable will put the chip into suspend, which is what we
> -	 * want as all outputs are disabled at this point
> +	 * The chip comes out of power-up in the sleep state,
> +	 * but force it to sleep in case it was woken up before
>  	 */
> +	pca9685_set_sleep_mode(pca, true);
> +	pm_runtime_set_suspended(&client->dev);
>  	pm_runtime_enable(&client->dev);
>  
> +	if (!IS_ENABLED(CONFIG_PM)) {
> +		/* Wake the chip up on non-PM environments */
> +		pca9685_set_sleep_mode(pca, false);

I admit I didn't grasp all the PM framework details, but I wonder if
it's right to first call set_sleep_mode(true) and then in some cases to
false again.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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