linux-kernel - Re: [PATCH v2 3/3] pwm: core: add consumer device link

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Date:   Mon, 11 Feb 2019 20:06:28 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Fabrice Gasnier <fabrice.gasnier@...com>
Cc:     thierry.reding@...il.com, robh+dt@...nel.org, tduszyns@...il.com,
        mark.rutland@....com, alexandre.torgue@...com,
        mcoquelin.stm32@...il.com, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH v2 3/3] pwm: core: add consumer device link

Hello Fabrice,

On Mon, Feb 11, 2019 at 05:12:02PM +0100, Fabrice Gasnier wrote:
> Add a device link between the PWM consumer and the PWM provider. This
> enforces the PWM user to get suspended before the PWM provider. It
> allows proper synchronization of suspend/resume sequences: the PWM user
> is responsible for properly stopping PWM, before the provider gets
> suspended: see [1]. Add the device link in:
> - pwm_get()
> - devm_pwm_get()
> - devm_of_pwm_get()
> as it requires a reference to the device for the PWM consumer.
> 
> [1] https://lkml.org/lkml/2019/2/5/770
> 
> Suggested-by: Thierry Reding <thierry.reding@...il.com>
> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@...com>
> ---
>  drivers/pwm/core.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 1581f6a..2835e27 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -770,8 +770,13 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>  	int err;
>  
>  	/* look up via DT first */
> -	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
> -		return of_pwm_get(dev->of_node, con_id);
> +	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node) {
> +		pwm = of_pwm_get(dev->of_node, con_id);
> +		if (!IS_ERR(pwm))
> +			device_link_add(dev, pwm->chip->dev,
> +					DL_FLAG_AUTOREMOVE_CONSUMER);
> +		return pwm;
> +	}
>  
>  	/*
>  	 * We look up the provider in the static table typically provided by
> @@ -851,6 +856,8 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>  	pwm->args.period = chosen->period;
>  	pwm->args.polarity = chosen->polarity;
>  
> +	device_link_add(dev, pwm->chip->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> +
>  	return pwm;
>  }
>  EXPORT_SYMBOL_GPL(pwm_get);
> @@ -943,6 +950,8 @@ struct pwm_device *devm_of_pwm_get(struct device *dev, struct device_node *np,
>  	if (!IS_ERR(pwm)) {
>  		*ptr = pwm;
>  		devres_add(dev, ptr);
> +		device_link_add(dev, pwm->chip->dev,
> +				DL_FLAG_AUTOREMOVE_CONSUMER);

IMHO it's surprising that devm_of_pwm_get() does more than of_pwm_get()
+ devres stuff. I'd put device_link_add() into of_pwm_get().

Best regards
Uwe

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