commit 459a25afe97cb3d7f978b90c881f4d7aac8fb755
author Boris BREZILLON <boris.brezillon@free-electrons.com> Wed Mar 30 22:03:27 2016 +0200
committer Thierry Reding <thierry.reding@gmail.com> Tue May 17 14:44:59 2016 +0200
tree 233902a29b5d0f418de168ffe531149b997cbcf4
parent 4ff66efd59102280a71d432c9f0e89cdaf66b849

pwm: Get rid of pwm->lock

PWM devices are not protected against concurrent accesses. The lock in
struct pwm_device might let PWM users think it is, but it's actually
only protecting the enabled state.

Removing this lock should be fine as long as all PWM users are aware
that accesses to the PWM device have to be serialized, which seems to be
the case for all of them except the sysfs interface. Patch the sysfs
code by adding a lock to the pwm_export struct and making sure it's
taken for all relevant accesses to the exported PWM device.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/sysfs.c

diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c
index 9c90886..187ca08 100644
--- a/drivers/pwm/sysfs.c
+++ b/drivers/pwm/sysfs.c
@@ -26,6 +26,7 @@
 struct pwm_export {
 	struct device child;
 	struct pwm_device *pwm;
+	struct mutex lock;
 };
 
 static struct pwm_export *child_to_pwm_export(struct device *child)
@@ -53,7 +54,8 @@
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
 	unsigned int val;
 	int ret;
 
@@ -61,7 +63,9 @@
 	if (ret)
 		return ret;
 
+	mutex_lock(&export->lock);
 	ret = pwm_config(pwm, pwm_get_duty_cycle(pwm), val);
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -79,7 +83,8 @@
 				struct device_attribute *attr,
 				const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
 	unsigned int val;
 	int ret;
 
@@ -87,7 +92,9 @@
 	if (ret)
 		return ret;
 
+	mutex_lock(&export->lock);
 	ret = pwm_config(pwm, val, pwm_get_period(pwm));
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -105,13 +112,16 @@
 			    struct device_attribute *attr,
 			    const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
 	int val, ret;
 
 	ret = kstrtoint(buf, 0, &val);
 	if (ret)
 		return ret;
 
+	mutex_lock(&export->lock);
+
 	switch (val) {
 	case 0:
 		pwm_disable(pwm);
@@ -124,6 +134,8 @@
 		break;
 	}
 
+	mutex_unlock(&export->lock);
+
 	return ret ? : size;
 }
 
@@ -151,7 +163,8 @@
 			      struct device_attribute *attr,
 			      const char *buf, size_t size)
 {
-	struct pwm_device *pwm = child_to_pwm_device(child);
+	struct pwm_export *export = child_to_pwm_export(child);
+	struct pwm_device *pwm = export->pwm;
 	enum pwm_polarity polarity;
 	int ret;
 
@@ -162,7 +175,9 @@
 	else
 		return -EINVAL;
 
+	mutex_lock(&export->lock);
 	ret = pwm_set_polarity(pwm, polarity);
+	mutex_unlock(&export->lock);
 
 	return ret ? : size;
 }
@@ -203,6 +218,7 @@
 	}
 
 	export->pwm = pwm;
+	mutex_init(&export->lock);
 
 	export->child.release = pwm_export_release;
 	export->child.parent = parent;