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
 
  */
 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
  * 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;
 
                struct backlight_properties *props;
                int brightness;
 
-               down(&pmac_backlight->sem);
                props = pmac_backlight->props;
 
                brightness = props->brightness +
                        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);
 }
        if (pmac_backlight) {
                struct backlight_properties *props;
 
-               down(&pmac_backlight->sem);
                props = pmac_backlight->props;
                props->brightness = brightness *
                        (props->max_brightness + 1) /
                else if (props->brightness < 0)
                        props->brightness = 0;
 
-               props->update_status(pmac_backlight);
-               up(&pmac_backlight->sem);
+               backlight_update_status(pmac_backlight);
 
                error = 0;
        }
        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);
 
 
                                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)
 
        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);
        }
 }
 
 
                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;
 }
 
                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)
        }
 
        /* Try to get brightness */
-       up(&pdata->bd->sem);
        brightness = appledisplay_bl_get_brightness(pdata->bd);
-       down(&pdata->bd->sem);
 
        if (brightness < 0) {
                retval = brightness;
        }
 
        /* 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);
 
        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);
                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);
 
        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);
                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);
 
                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);
 
                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;
        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);
                        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;
                }
        }
        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));
 
                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;
 
                 * 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);
        /* 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 */
 
        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);
                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);
 
        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);
                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);
 
 #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;
 
        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);
 
 #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;
 
        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);