backlight: Fix external uses of backlight internal semaphore
backlight_device->sem has a very specific use as documented in the
header file. The external users of this are using it for a different
reason, to serialise access to the update_status() method.
backlight users were supposed to implement their own internal
serialisation of update_status() if needed but everyone is doing
things differently and incorrectly. Therefore add a global mutex to
take care of serialisation for everyone, once and for all.
Locking for get_brightness remains optional since most users don't
need it.
Also update the lcd class in a similar way.
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
diff --git a/include/linux/lcd.h b/include/linux/lcd.h
index 8a468f1..bfbf655 100644
--- a/include/linux/lcd.h
+++ b/include/linux/lcd.h
@@ -9,8 +9,24 @@
#define _LINUX_LCD_H
#include <linux/device.h>
+#include <linux/mutex.h>
#include <linux/notifier.h>
+/* Notes on locking:
+ *
+ * lcd_device->sem is an internal backlight lock protecting the props
+ * field and no code outside the core should need to touch it.
+ *
+ * Access to set_power() is serialised by the update_lock mutex since
+ * most drivers seem to need this and historically get it wrong.
+ *
+ * Most drivers don't need locking on their get_power() method.
+ * If yours does, you need to implement it in the driver. You can use the
+ * update_lock mutex if appropriate.
+ *
+ * Any other use of the locks below is probably wrong.
+ */
+
struct lcd_device;
struct fb_info;
@@ -39,12 +55,22 @@
struct semaphore sem;
/* If this is NULL, the backing module is unloaded */
struct lcd_properties *props;
+ /* Serialise access to set_power method */
+ struct mutex update_lock;
/* The framebuffer notifier block */
struct notifier_block fb_notif;
/* The class device structure */
struct class_device class_dev;
};
+static inline void lcd_set_power(struct lcd_device *ld, int power)
+{
+ mutex_lock(&ld->update_lock);
+ if (ld->props && ld->props->set_power)
+ ld->props->set_power(ld, power);
+ mutex_unlock(&ld->update_lock);
+}
+
extern struct lcd_device *lcd_device_register(const char *name,
void *devdata, struct lcd_properties *lp);
extern void lcd_device_unregister(struct lcd_device *ld);