leds: implement sysfs interface locking mechanism

Add a mechanism for locking LED subsystem sysfs interface.
This patch prepares ground for addition of LED Flash Class
extension, whose API will be integrated with V4L2 Flash API.
Such a fusion enforces introducing a locking scheme, which
will secure consistent access to the LED Flash Class device.

The mechanism being introduced allows for disabling LED
subsystem sysfs interface by calling led_sysfs_disable function
and enabling it by calling led_sysfs_enable. The functions
alter the LED_SYSFS_DISABLE flag state and must be called
under mutex lock. The state of the lock is checked with use
of led_sysfs_is_disabled function. Such a design allows for
providing immediate feedback to the user space on whether
the LED Flash Class device is available or is under V4L2 Flash
sub-device control.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

3 files changed, 47 insertions, 6 deletions

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 7440c58b8e6f..65722deb8d28 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -40,17 +40,27 @@ static ssize_t brightness_store(struct device *dev,
 {
         struct led_classdev *led_cdev = dev_get_drvdata(dev);
         unsigned long state;
-        ssize_t ret = -EINVAL;
+        ssize_t ret;
+
+        mutex_lock(&led_cdev->led_access);
+
+        if (led_sysfs_is_disabled(led_cdev)) {
+                ret = -EBUSY;
+                goto unlock;
+        }
 
         ret = kstrtoul(buf, 10, &state);
         if (ret)
-                return ret;
+                goto unlock;
 
         if (state == LED_OFF)
                 led_trigger_remove(led_cdev);
         __led_set_brightness(led_cdev, state);
 
-        return size;
+        ret = size;
+unlock:
+        mutex_unlock(&led_cdev->led_access);
+        return ret;
 }
 static DEVICE_ATTR_RW(brightness);
 
@@ -214,6 +224,7 @@ int led_classdev_register(struct device *parent, struct led_classdev *led_cdev)
 #ifdef CONFIG_LEDS_TRIGGERS
         init_rwsem(&led_cdev->trigger_lock);
 #endif
+        mutex_init(&led_cdev->led_access);
         /* add to the list of leds */
         down_write(&leds_list_lock);
         list_add_tail(&led_cdev->node, &leds_list);
@@ -267,6 +278,8 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
         down_write(&leds_list_lock);
         list_del(&led_cdev->node);
         up_write(&leds_list_lock);
+
+        mutex_destroy(&led_cdev->led_access);
 }
 EXPORT_SYMBOL_GPL(led_classdev_unregister);
 
diff --git a/drivers/leds/led-core.c b/drivers/leds/led-core.c
index aaa8eba9099f..be6d9fa5e971 100644
--- a/drivers/leds/led-core.c
+++ b/drivers/leds/led-core.c
@@ -143,3 +143,21 @@ int led_update_brightness(struct led_classdev *led_cdev)
         return ret;
 }
 EXPORT_SYMBOL(led_update_brightness);
+
+/* Caller must ensure led_cdev->led_access held */
+void led_sysfs_disable(struct led_classdev *led_cdev)
+{
+        lockdep_assert_held(&led_cdev->led_access);
+
+        led_cdev->flags |= LED_SYSFS_DISABLE;
+}
+EXPORT_SYMBOL_GPL(led_sysfs_disable);
+
+/* Caller must ensure led_cdev->led_access held */
+void led_sysfs_enable(struct led_classdev *led_cdev)
+{
+        lockdep_assert_held(&led_cdev->led_access);
+
+        led_cdev->flags &= ~LED_SYSFS_DISABLE;
+}
+EXPORT_SYMBOL_GPL(led_sysfs_enable);
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index c3734f10fdd5..e8b1120f486d 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -37,6 +37,14 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
         char trigger_name[TRIG_NAME_MAX];
         struct led_trigger *trig;
         size_t len;
+        int ret = count;
+
+        mutex_lock(&led_cdev->led_access);
+
+        if (led_sysfs_is_disabled(led_cdev)) {
+                ret = -EBUSY;
+                goto unlock;
+        }
 
         trigger_name[sizeof(trigger_name) - 1] = '\0';
         strncpy(trigger_name, buf, sizeof(trigger_name) - 1);
@@ -47,7 +55,7 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
 
         if (!strcmp(trigger_name, "none")) {
                 led_trigger_remove(led_cdev);
-                return count;
+                goto unlock;
         }
 
         down_read(&triggers_list_lock);
@@ -58,12 +66,14 @@ ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
                         up_write(&led_cdev->trigger_lock);
 
                         up_read(&triggers_list_lock);
-                        return count;
+                        goto unlock;
                 }
         }
         up_read(&triggers_list_lock);
 
-        return -EINVAL;
+unlock:
+        mutex_unlock(&led_cdev->led_access);
+        return ret;
 }
 EXPORT_SYMBOL_GPL(led_trigger_store);