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 <[e-mail]>

arch/powerpc/kernel/traps.c

···
 	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

arch/powerpc/platforms/powermac/backlight.c

···
  */
 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);
 

drivers/macintosh/via-pmu-backlight.c

···
 				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)

drivers/misc/asus-laptop.c

···
 	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;
 }

drivers/usb/misc/appledisplay.c

···
 		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);

drivers/video/aty/aty128fb.c

···
 	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);

drivers/video/aty/atyfb_base.c

···
 	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);

drivers/video/aty/radeon_backlight.c

···
 		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);

drivers/video/backlight/backlight.c

···
 		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));

drivers/video/backlight/lcd.c

···
 		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;

drivers/video/chipsfb.c

···
 		 * 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 */

drivers/video/nvidia/nv_backlight.c

···
 	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);

drivers/video/riva/fbdev.c

···
 	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);

include/linux/backlight.h

···
 #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);

include/linux/lcd.h

···
 #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);