Add locking around the background L2x0 cache operations

The background operations of the L2x0 cache controllers are aborted if
another operation is issued on the same or different core. This patch
protects the maintenance operation issuing/polling with a spinlock.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/mm/cache-l2x0.c

@@ -17,6 +17,7 @@
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
  */
 #include <linux/init.h>
+#include <linux/spinlock.h>
 
 #include <asm/cacheflush.h>
 #include <asm/io.h>
@@ -25,14 +26,19 @@
 #define CACHE_LINE_SIZE		32
 
 static void __iomem *l2x0_base;
+static DEFINE_SPINLOCK(l2x0_lock);
 
 static inline void sync_writel(unsigned long val, unsigned long reg,
 			       unsigned long complete_mask)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&l2x0_lock, flags);
 	writel(val, l2x0_base + reg);
 	/* wait for the operation to complete */
 	while (readl(l2x0_base + reg) & complete_mask)
 		;
+	spin_unlock_irqrestore(&l2x0_lock, flags);
 }
 
 static inline void cache_sync(void)