ARM: l2c: only write the auxiliary control register if required

Avoid unnecessary writes to the auxiliary control register if the
register already contains the required value.  This allows us to
avoid invoking the platforms secure monitor code unnecessarily.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mm/cache-l2x0.c

@@ -92,7 +92,9 @@ static void l2c_enable(void __iomem *base, u32 aux, unsigned num_lock)
 {
 	unsigned long flags;
 
-	writel_relaxed(aux, base + L2X0_AUX_CTRL);
+	/* Only write the aux register if it needs changing */
+	if (readl_relaxed(base + L2X0_AUX_CTRL) != aux)
+		writel_relaxed(aux, base + L2X0_AUX_CTRL);
 
 	l2c_unlock(base, num_lock);