[PATCH 2/6] backlight: use spin-lock to protect device list

[Marta Lofstedt]

From: David Herrmann <dh.herrmann at gmail.com>

There is really no reason to use a mutex to protect a simple list. Convert
the list-lock to a simple spinlock instead.

The spin-locks prepare for a backlight_find() helper, which should
preferably be usable from atomic context. A mutex would prevent that, so
use an irq-save spinlock instead.

Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
---
 drivers/video/backlight/backlight.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 37f6173..716c091 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -16,13 +16,14 @@
 #include <linux/err.h>
 #include <linux/fb.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 
 #ifdef CONFIG_PMAC_BACKLIGHT
 #include <asm/backlight.h>
 #endif
 
 static LIST_HEAD(backlight_dev_list);
-static DEFINE_MUTEX(backlight_dev_list_mutex);
+static DEFINE_SPINLOCK(backlight_dev_list_lock);
 static BLOCKING_NOTIFIER_HEAD(backlight_notifier);
 
 static const char *const backlight_types[] = {
@@ -378,9 +379,9 @@ struct backlight_device *backlight_device_register(const char *name,
 	mutex_unlock(&pmac_backlight_mutex);
 #endif
 
-	mutex_lock(&backlight_dev_list_mutex);
+	spin_lock_irq(&backlight_dev_list_lock);
 	list_add(&new_bd->entry, &backlight_dev_list);
-	mutex_unlock(&backlight_dev_list_mutex);
+	spin_unlock_irq(&backlight_dev_list_lock);
 
 	blocking_notifier_call_chain(&backlight_notifier,
 				     BACKLIGHT_REGISTERED, new_bd);
@@ -393,15 +394,16 @@ struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
 {
 	bool found = false;
 	struct backlight_device *bd;
+	unsigned long flags;
 
-	mutex_lock(&backlight_dev_list_mutex);
+	spin_lock_irqsave(&backlight_dev_list_lock, flags);
 	list_for_each_entry(bd, &backlight_dev_list, entry) {
 		if (bd->props.type == type) {
 			found = true;
 			break;
 		}
 	}
-	mutex_unlock(&backlight_dev_list_mutex);
+	spin_unlock_irqrestore(&backlight_dev_list_lock, flags);
 
 	return found ? bd : NULL;
 }
@@ -418,9 +420,9 @@ void backlight_device_unregister(struct backlight_device *bd)
 	if (!bd)
 		return;
 
-	mutex_lock(&backlight_dev_list_mutex);
+	spin_lock_irq(&backlight_dev_list_lock);
 	list_del(&bd->entry);
-	mutex_unlock(&backlight_dev_list_mutex);
+	spin_unlock_irq(&backlight_dev_list_lock);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
 	mutex_lock(&pmac_backlight_mutex);
-- 
2.9.3