backlight: update bd state & fb_blank properties when necessary

We don't have to update the state and fb_blank properties of a backlight
device every time a blanking or unblanking event comes because they may
have already been what we want.  Another thought is that one backlight
device may be shared by multiple framebuffers.  The backlight driver
should take the backlight device as a resource shared by all the
associated framebuffers.

This patch adds some logic to record each framebuffer's backlight usage
to determine the backlight device use count and whether the two
properties should be updated or not.  To be more specific, only one
unblank operation on a certain blanked framebuffer may increase the
backlight device's use count by one, while one blank operation on a
certain unblanked framebuffer may decrease the use count by one, because
the userspace is likely to unblank an unblanked framebuffer or blank a
blanked framebuffer.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/video/backlight/backlight.c

@@ -41,6 +41,8 @@ static int fb_notifier_callback(struct notifier_block *self,
 {
 	struct backlight_device *bd;
 	struct fb_event *evdata = data;
+	int node = evdata->info->node;
+	int fb_blank = 0;
 
 	/* If we aren't interested in this event, skip it immediately ... */
 	if (event != FB_EVENT_BLANK && event != FB_EVENT_CONBLANK)
@@ -51,11 +53,22 @@ static int fb_notifier_callback(struct notifier_block *self,
 	if (bd->ops)
 		if (!bd->ops->check_fb ||
 		    bd->ops->check_fb(bd, evdata->info)) {
-			bd->props.fb_blank = *(int *)evdata->data;
-			if (bd->props.fb_blank == FB_BLANK_UNBLANK)
-				bd->props.state &= ~BL_CORE_FBBLANK;
-			else
-				bd->props.state |= BL_CORE_FBBLANK;
+			fb_blank = *(int *)evdata->data;
+			if (fb_blank == FB_BLANK_UNBLANK &&
+			    !bd->fb_bl_on[node]) {
+				bd->fb_bl_on[node] = true;
+				if (!bd->use_count++) {
+					bd->props.state &= ~BL_CORE_FBBLANK;
+					bd->props.fb_blank = FB_BLANK_UNBLANK;
+				}
+			} else if (fb_blank != FB_BLANK_UNBLANK &&
+				   bd->fb_bl_on[node]) {
+				bd->fb_bl_on[node] = false;
+				if (!(--bd->use_count)) {
+					bd->props.state |= BL_CORE_FBBLANK;
+					bd->props.fb_blank = fb_blank;
+				}
+			}
 			backlight_update_status(bd);
 		}
 	mutex_unlock(&bd->ops_lock);

include/linux/backlight.h

@@ -9,6 +9,7 @@
 #define _LINUX_BACKLIGHT_H
 
 #include <linux/device.h>
+#include <linux/fb.h>
 #include <linux/mutex.h>
 #include <linux/notifier.h>
 
@@ -104,6 +105,11 @@ struct backlight_device {
 	struct list_head entry;
 
 	struct device dev;
+
+	/* Multiple framebuffers may share one backlight device */
+	bool fb_bl_on[FB_MAX];
+
+	int use_count;
 };
 
 static inline void backlight_update_status(struct backlight_device *bd)