linux-kernel - Re: [PATCH v4 3/3] pwm: core: add consumer device link

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Message-ID: <20190219085516.dz5ux37kdszqkisy@pengutronix.de>
Date:   Tue, 19 Feb 2019 09:55:16 +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 v4 3/3] pwm: core: add consumer device link

On Tue, Feb 19, 2019 at 09:46:32AM +0100, Fabrice Gasnier wrote:
> On 2/18/19 6:22 PM, Uwe Kleine-König wrote:
> > Hello,
> > 
> > On Thu, Feb 14, 2019 at 11:25:51AM +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:
> >> - of_pwm_get()
> >> - pwm_get()
> >> - devm_*pwm_get() variants
> >> 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>
> >> ---
> >> Changes in v4:
> >> - rework error handling following Thierry's comments
> >> - turn/split pr_debug() into dev_err()/pr_warn().
> >>
> >> Changes in v3:
> >> - add struct device to of_get_pwm() arguments to handle device link from
> >>   there as discussed with Uwe.
> >> ---
> >>  drivers/pwm/core.c  | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
> >>  include/linux/pwm.h |  6 ++++--
> >>  2 files changed, 51 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> >> index 1581f6a..64e10a6 100644
> >> --- a/drivers/pwm/core.c
> >> +++ b/drivers/pwm/core.c
> >> @@ -636,8 +636,35 @@ static struct pwm_chip *of_node_to_pwmchip(struct device_node *np)
> >>  	return ERR_PTR(-EPROBE_DEFER);
> >>  }
> >>  
> >> +static struct device_link *pwm_device_link_add(struct device *dev,
> >> +					       struct pwm_device *pwm)
> >> +{
> >> +	struct device_link *dl;
> >> +
> >> +	if (!dev) {
> >> +		/*
> >> +		 * No device for the PWM consumer has been provided. It may
> >> +		 * impact the PM sequence ordering: the PWM supplier may get
> >> +		 * suspended before the consumer.
> >> +		 */
> >> +		pr_warn("no consumer dev, can't create device link to %s\n",
> >> +			dev_name(pwm->chip->dev));
> > 
> > Maybe use dev_warn(pwm->chip->dev, ...) ?
> 
> Hi Uwe,
> 
> I'm wondering a bit about this: In this case, the caller that doesn't
> provide a struct device *, PWM provider isn't responsible for that. So I
> just hope this wouldn't be miss-leading ?

IMHO it's more the wording that might make the message misleading. If
you use

	dev_warn(pwm->chip->dev, "No consumer device specified to create a device link to\n");

that's completely fine in my eyes.
 
Best regards
Uwe

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