mtd: maps: sa1100-flash: Add reference counter to set_vpp()

This patch is part of a set which fixes unnecessary flash erase and write errors
resulting from the MTD CFI driver turning off vpp while an erase is in progress.
This patch allows sa1100_set_vpp() calls to be nested by adding a reference
counter.
Signed-off-by: NPaul Parsons <lost.distance@yahoo.com>
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/maps/sa1100-flash.c

@@ -36,10 +36,22 @@ struct sa_info {
 	struct sa_subdev_info	subdev[0];
 };
 
+static DEFINE_SPINLOCK(sa1100_vpp_lock);
+static int sa1100_vpp_refcnt;
 static void sa1100_set_vpp(struct map_info *map, int on)
 {
 	struct sa_subdev_info *subdev = container_of(map, struct sa_subdev_info, map);
-	subdev->plat->set_vpp(on);
+	unsigned long flags;
+
+	spin_lock_irqsave(&sa1100_vpp_lock, flags);
+	if (on) {
+		if (++sa1100_vpp_refcnt == 1)   /* first nested 'on' */
+			subdev->plat->set_vpp(1);
+	} else {
+		if (--sa1100_vpp_refcnt == 0)   /* last nested 'off' */
+			subdev->plat->set_vpp(0);
+	}
+	spin_unlock_irqrestore(&sa1100_vpp_lock, flags);
 }
 
 static void sa1100_destroy_subdev(struct sa_subdev_info *subdev)