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>

15 files changed, 76 insertions, 76 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index dcc6f159fd94..35ce07b6a5bc 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -107,12 +107,10 @@ int die(const char *str, struct pt_regs *regs, long err)
         if (machine_is(powermac) && pmac_backlight) {
                 struct backlight_properties *props;
 
-                down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
                 props->brightness = props->max_brightness;
                 props->power = FB_BLANK_UNBLANK;
-                props->update_status(pmac_backlight);
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
         }
         mutex_unlock(&pmac_backlight_mutex);
 #endif
diff --git a/arch/powerpc/platforms/powermac/backlight.c b/arch/powerpc/platforms/powermac/backlight.c
index c3a89414ddc0..1be358c1448a 100644
--- a/arch/powerpc/platforms/powermac/backlight.c
+++ b/arch/powerpc/platforms/powermac/backlight.c
@@ -37,7 +37,9 @@ static int pmac_backlight_set_legacy_queued;
  */
 static atomic_t kernel_backlight_disabled = ATOMIC_INIT(0);
 
-/* Protect the pmac_backlight variable */
+/* Protect the pmac_backlight variable below.
+   You should hold this lock when using the pmac_backlight pointer to
+   prevent its potential removal. */
 DEFINE_MUTEX(pmac_backlight_mutex);
 
 /* Main backlight storage
@@ -49,9 +51,6 @@ DEFINE_MUTEX(pmac_backlight_mutex);
  * internal display, it doesn't matter. Other backlight drivers can be used
  * independently.
  *
- * Lock ordering:
- * pmac_backlight_mutex (global, main backlight)
- *   pmac_backlight->sem (backlight class)
  */
 struct backlight_device *pmac_backlight;
 
@@ -104,7 +103,6 @@ static void pmac_backlight_key_worker(struct work_struct *work)
                 struct backlight_properties *props;
                 int brightness;
 
-                down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
 
                 brightness = props->brightness +
@@ -117,9 +115,7 @@ static void pmac_backlight_key_worker(struct work_struct *work)
                         brightness = props->max_brightness;
 
                 props->brightness = brightness;
-                props->update_status(pmac_backlight);
-
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
         }
         mutex_unlock(&pmac_backlight_mutex);
 }
@@ -145,7 +141,6 @@ static int __pmac_backlight_set_legacy_brightness(int brightness)
         if (pmac_backlight) {
                 struct backlight_properties *props;
 
-                down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
                 props->brightness = brightness *
                         (props->max_brightness + 1) /
@@ -156,8 +151,7 @@ static int __pmac_backlight_set_legacy_brightness(int brightness)
                 else if (props->brightness < 0)
                         props->brightness = 0;
 
-                props->update_status(pmac_backlight);
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
 
                 error = 0;
         }
@@ -196,14 +190,11 @@ int pmac_backlight_get_legacy_brightness()
         if (pmac_backlight) {
                 struct backlight_properties *props;
 
-                down(&pmac_backlight->sem);
                 props = pmac_backlight->props;
 
                 result = props->brightness *
                         (OLD_BACKLIGHT_MAX + 1) /
                         (props->max_brightness + 1);
-
-                up(&pmac_backlight->sem);
         }
         mutex_unlock(&pmac_backlight_mutex);
 
diff --git a/drivers/macintosh/via-pmu-backlight.c b/drivers/macintosh/via-pmu-backlight.c
index db8bcc35bc03..7ba2042b2dd0 100644
--- a/drivers/macintosh/via-pmu-backlight.c
+++ b/drivers/macintosh/via-pmu-backlight.c
@@ -166,11 +166,9 @@ void __init pmu_backlight_init()
                                 pmu_backlight_data.max_brightness / 15);
         }
 
-        down(&bd->sem);
         bd->props->brightness = level;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
         mutex_lock(&pmac_backlight_mutex);
         if (!pmac_backlight)
diff --git a/drivers/misc/asus-laptop.c b/drivers/misc/asus-laptop.c
index d15ee5e34201..7ace5b9a3d28 100644
--- a/drivers/misc/asus-laptop.c
+++ b/drivers/misc/asus-laptop.c
@@ -348,13 +348,8 @@ static void lcd_blank(int blank)
         struct backlight_device *bd = asus_backlight_device;
 
         if (bd) {
-                down(&bd->sem);
-                if (likely(bd->props)) {
-                        bd->props->power = blank;
-                        if (likely(bd->props->update_status))
-                                bd->props->update_status(bd);
-                }
-                up(&bd->sem);
+                bd->props->power = blank;
+                backlight_update_status(bd);
         }
 }
 
@@ -1028,14 +1023,9 @@ static int asus_backlight_init(struct device *dev)
 
                 asus_backlight_device = bd;
 
-                down(&bd->sem);
-                if (likely(bd->props)) {
-                        bd->props->brightness = read_brightness(NULL);
-                        bd->props->power = FB_BLANK_UNBLANK;
-                        if (likely(bd->props->update_status))
-                                bd->props->update_status(bd);
-                }
-                up(&bd->sem);
+                bd->props->brightness = read_brightness(NULL);
+                bd->props->power = FB_BLANK_UNBLANK;
+                backlight_update_status(bd);
         }
         return 0;
 }
diff --git a/drivers/usb/misc/appledisplay.c b/drivers/usb/misc/appledisplay.c
index 416cde5893af..cd2c5574cf93 100644
--- a/drivers/usb/misc/appledisplay.c
+++ b/drivers/usb/misc/appledisplay.c
@@ -189,11 +189,9 @@ static void appledisplay_work(struct work_struct *work)
                 container_of(work, struct appledisplay, work.work);
         int retval;
 
-        up(&pdata->bd->sem);
         retval = appledisplay_bl_get_brightness(pdata->bd);
         if (retval >= 0)
                 pdata->bd->props->brightness = retval;
-        down(&pdata->bd->sem);
 
         /* Poll again in about 125ms if there's still a button pressed */
         if (pdata->button_pressed)
@@ -288,9 +286,7 @@ static int appledisplay_probe(struct usb_interface *iface,
         }
 
         /* Try to get brightness */
-        up(&pdata->bd->sem);
         brightness = appledisplay_bl_get_brightness(pdata->bd);
-        down(&pdata->bd->sem);
 
         if (brightness < 0) {
                 retval = brightness;
@@ -299,9 +295,7 @@ static int appledisplay_probe(struct usb_interface *iface,
         }
 
         /* Set brightness in backlight device */
-        up(&pdata->bd->sem);
         pdata->bd->props->brightness = brightness;
-        down(&pdata->bd->sem);
 
         /* save our data pointer in the interface device */
         usb_set_intfdata(iface, pdata);
diff --git a/drivers/video/aty/aty128fb.c b/drivers/video/aty/aty128fb.c
index 1fa211c0d7bb..5d8f73b2b66f 100644
--- a/drivers/video/aty/aty128fb.c
+++ b/drivers/video/aty/aty128fb.c
@@ -1807,10 +1807,8 @@ static void aty128_bl_set_power(struct fb_info *info, int power)
         mutex_lock(&info->bl_mutex);
 
         if (info->bl_dev) {
-                down(&info->bl_dev->sem);
                 info->bl_dev->props->power = power;
                 __aty128_bl_update_status(info->bl_dev);
-                up(&info->bl_dev->sem);
         }
 
         mutex_unlock(&info->bl_mutex);
@@ -1847,11 +1845,9 @@ static void aty128_bl_init(struct aty128fb_par *par)
                 219 * FB_BACKLIGHT_MAX / MAX_LEVEL);
         mutex_unlock(&info->bl_mutex);
 
-        down(&bd->sem);
         bd->props->brightness = aty128_bl_data.max_brightness;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
         mutex_lock(&pmac_backlight_mutex);
diff --git a/drivers/video/aty/atyfb_base.c b/drivers/video/aty/atyfb_base.c
index 5ea5a00e58a3..23deb3566020 100644
--- a/drivers/video/aty/atyfb_base.c
+++ b/drivers/video/aty/atyfb_base.c
@@ -2188,10 +2188,8 @@ static void aty_bl_set_power(struct fb_info *info, int power)
         mutex_lock(&info->bl_mutex);
 
         if (info->bl_dev) {
-                down(&info->bl_dev->sem);
                 info->bl_dev->props->power = power;
                 __aty_bl_update_status(info->bl_dev);
-                up(&info->bl_dev->sem);
         }
 
         mutex_unlock(&info->bl_mutex);
@@ -2224,11 +2222,9 @@ static void aty_bl_init(struct atyfb_par *par)
                 0xFF * FB_BACKLIGHT_MAX / MAX_LEVEL);
         mutex_unlock(&info->bl_mutex);
 
-        down(&bd->sem);
         bd->props->brightness = aty_bl_data.max_brightness;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
         mutex_lock(&pmac_backlight_mutex);
diff --git a/drivers/video/aty/radeon_backlight.c b/drivers/video/aty/radeon_backlight.c
index 8b66df6f199a..9cfcecac8b5e 100644
--- a/drivers/video/aty/radeon_backlight.c
+++ b/drivers/video/aty/radeon_backlight.c
@@ -194,11 +194,9 @@ void radeonfb_bl_init(struct radeonfb_info *rinfo)
                 217 * FB_BACKLIGHT_MAX / MAX_RADEON_LEVEL);
         mutex_unlock(&rinfo->info->bl_mutex);
 
-        down(&bd->sem);
         bd->props->brightness = radeon_bl_data.max_brightness;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
         mutex_lock(&pmac_backlight_mutex);
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 7a85be4d2b0a..347081daf7a4 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -37,8 +37,7 @@ static int fb_notifier_callback(struct notifier_block *self,
                 if (!bd->props->check_fb ||
                     bd->props->check_fb(evdata->info)) {
                         bd->props->fb_blank = *(int *)evdata->data;
-                        if (bd->props && bd->props->update_status)
-                                bd->props->update_status(bd);
+                        backlight_update_status(bd);
                 }
         up(&bd->sem);
         return 0;
@@ -97,8 +96,7 @@ static ssize_t backlight_store_power(struct class_device *cdev, const char *buf,
         if (bd->props) {
                 pr_debug("backlight: set power to %d\n", power);
                 bd->props->power = power;
-                if (bd->props->update_status)
-                        bd->props->update_status(bd);
+                backlight_update_status(bd);
                 rc = count;
         }
         up(&bd->sem);
@@ -140,8 +138,7 @@ static ssize_t backlight_store_brightness(struct class_device *cdev, const char
                         pr_debug("backlight: set brightness to %d\n",
                                  brightness);
                         bd->props->brightness = brightness;
-                        if (bd->props->update_status)
-                                bd->props->update_status(bd);
+                        backlight_update_status(bd);
                         rc = count;
                 }
         }
@@ -230,6 +227,7 @@ struct backlight_device *backlight_device_register(const char *name,
         if (!new_bd)
                 return ERR_PTR(-ENOMEM);
 
+        mutex_init(&new_bd->update_lock);
         init_MUTEX(&new_bd->sem);
         new_bd->props = bp;
         memset(&new_bd->class_dev, 0, sizeof(new_bd->class_dev));
diff --git a/drivers/video/backlight/lcd.c b/drivers/video/backlight/lcd.c
index 959024812abc..1e1e61a4b5da 100644
--- a/drivers/video/backlight/lcd.c
+++ b/drivers/video/backlight/lcd.c
@@ -198,6 +198,7 @@ struct lcd_device *lcd_device_register(const char *name, void *devdata,
                 return ERR_PTR(-ENOMEM);
 
         init_MUTEX(&new_ld->sem);
+        mutex_init(&new_ld->update_lock);
         new_ld->props = lp;
         memset(&new_ld->class_dev, 0, sizeof(new_ld->class_dev));
         new_ld->class_dev.class = &lcd_class;
diff --git a/drivers/video/chipsfb.c b/drivers/video/chipsfb.c
index 73cb426bf2d7..9a656bc6295c 100644
--- a/drivers/video/chipsfb.c
+++ b/drivers/video/chipsfb.c
@@ -153,13 +153,11 @@ static int chipsfb_blank(int blank, struct fb_info *info)
                  * useful at blank = 1 too (saves battery, extends backlight
                  * life)
                  */
-                down(&pmac_backlight->sem);
                 if (blank)
                         pmac_backlight->props->power = FB_BLANK_POWERDOWN;
                 else
                         pmac_backlight->props->power = FB_BLANK_UNBLANK;
-                pmac_backlight->props->update_status(pmac_backlight);
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
         }
 
         mutex_unlock(&pmac_backlight_mutex);
@@ -415,10 +413,8 @@ chipsfb_pci_init(struct pci_dev *dp, const struct pci_device_id *ent)
         /* turn on the backlight */
         mutex_lock(&pmac_backlight_mutex);
         if (pmac_backlight) {
-                down(&pmac_backlight->sem);
                 pmac_backlight->props->power = FB_BLANK_UNBLANK;
-                pmac_backlight->props->update_status(pmac_backlight);
-                up(&pmac_backlight->sem);
+                backlight_update_status(pmac_backlight);
         }
         mutex_unlock(&pmac_backlight_mutex);
 #endif /* CONFIG_PMAC_BACKLIGHT */
diff --git a/drivers/video/nvidia/nv_backlight.c b/drivers/video/nvidia/nv_backlight.c
index 4254c090dc4b..f5e42d0bd0da 100644
--- a/drivers/video/nvidia/nv_backlight.c
+++ b/drivers/video/nvidia/nv_backlight.c
@@ -114,10 +114,8 @@ void nvidia_bl_set_power(struct fb_info *info, int power)
         mutex_lock(&info->bl_mutex);
 
         if (info->bl_dev) {
-                down(&info->bl_dev->sem);
                 info->bl_dev->props->power = power;
                 __nvidia_bl_update_status(info->bl_dev);
-                up(&info->bl_dev->sem);
         }
 
         mutex_unlock(&info->bl_mutex);
@@ -154,11 +152,9 @@ void nvidia_bl_init(struct nvidia_par *par)
                 0x534 * FB_BACKLIGHT_MAX / MAX_LEVEL);
         mutex_unlock(&info->bl_mutex);
 
-        down(&bd->sem);
         bd->props->brightness = nvidia_bl_data.max_brightness;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
         mutex_lock(&pmac_backlight_mutex);
diff --git a/drivers/video/riva/fbdev.c b/drivers/video/riva/fbdev.c
index fd825711bb63..b70d18f7fcd9 100644
--- a/drivers/video/riva/fbdev.c
+++ b/drivers/video/riva/fbdev.c
@@ -357,10 +357,8 @@ static void riva_bl_set_power(struct fb_info *info, int power)
         mutex_lock(&info->bl_mutex);
 
         if (info->bl_dev) {
-                down(&info->bl_dev->sem);
                 info->bl_dev->props->power = power;
                 __riva_bl_update_status(info->bl_dev);
-                up(&info->bl_dev->sem);
         }
 
         mutex_unlock(&info->bl_mutex);
@@ -397,11 +395,9 @@ static void riva_bl_init(struct riva_par *par)
                 FB_BACKLIGHT_MAX);
         mutex_unlock(&info->bl_mutex);
 
-        down(&bd->sem);
         bd->props->brightness = riva_bl_data.max_brightness;
         bd->props->power = FB_BLANK_UNBLANK;
-        bd->props->update_status(bd);
-        up(&bd->sem);
+        backlight_update_status(bd);
 
 #ifdef CONFIG_PMAC_BACKLIGHT
         mutex_lock(&pmac_backlight_mutex);
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 <linux/device.h>
+#include <linux/mutex.h>
 #include <linux/notifier.h>
 
+/* 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);
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);