diff options
author | Richard Purdie <rpurdie@rpsys.net> | 2007-02-09 01:25:09 +0300 |
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committer | Richard Purdie <rpurdie@rpsys.net> | 2007-02-20 11:38:45 +0300 |
commit | 28ee086d5b36aab2931f6740e409bb0fb6c65e5f (patch) | |
tree | 0a308c80affcc39c2c869f29f1109e5ee9d6140f /include/linux/lcd.h | |
parent | a8db3c1948eb30cd6988b5b96b654f591e6280b1 (diff) | |
download | linux-28ee086d5b36aab2931f6740e409bb0fb6c65e5f.tar.xz |
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>
Diffstat (limited to 'include/linux/lcd.h')
-rw-r--r-- | include/linux/lcd.h | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/include/linux/lcd.h b/include/linux/lcd.h index 8a468f168c45..bfbf6552eb51 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 lcd_device { 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); |