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

From: Uwe Kleine-König
Date: Tue Feb 19 2019 - 03:55:26 EST


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@xxxxxxxxx>
> >> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@xxxxxx>
> >> ---
> >> 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

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