[PATCH v2 3/3] pwm: core: add consumer device link

[Fabrice Gasnier <fabrice.gasnier@st.com>]

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@gmail.com>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.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);
 	} else {
 		devres_free(ptr);
 	}
-- 
1.9.1