From 28ee086d5b36aab2931f6740e409bb0fb6c65e5f Mon Sep 17 00:00:00 2001 From: Richard Purdie Date: Thu, 8 Feb 2007 22:25:09 +0000 Subject: 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 --- include/linux/backlight.h | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'include/linux/backlight.h') diff --git a/include/linux/backlight.h b/include/linux/backlight.h index 287c62d956f2..d1426b852bdf 100644 --- a/include/linux/backlight.h +++ b/include/linux/backlight.h @@ -9,8 +9,24 @@ #define _LINUX_BACKLIGHT_H #include +#include #include +/* Notes on locking: + * + * backlight_device->sem is an internal backlight lock protecting the props + * field and no code outside the core should need to touch it. + * + * Access to update_status() 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_brightness() 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 backlight_device; struct fb_info; @@ -44,12 +60,22 @@ struct backlight_device { struct semaphore sem; /* If this is NULL, the backing module is unloaded */ struct backlight_properties *props; + /* Serialise access to update_status 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 backlight_update_status(struct backlight_device *bd) +{ + mutex_lock(&bd->update_lock); + if (bd->props && bd->props->update_status) + bd->props->update_status(bd); + mutex_unlock(&bd->update_lock); +} + extern struct backlight_device *backlight_device_register(const char *name, struct device *dev,void *devdata,struct backlight_properties *bp); extern void backlight_device_unregister(struct backlight_device *bd); -- cgit v1.2.3-59-g8ed1b