drivers/rtc/rtc-twl.c: optimize IRQ bit access

As the TWL RTC driver has a cached copy of enabled RTC interrupt bits in
variable rtc_irq_bits, that can be checked before really setting or
masking any of the interrupt bits.
Signed-off-by: Venu Byravarasu <vbyravarasu@nvidia.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-twl.c

@@ -176,6 +176,10 @@ static int set_rtc_irq_bit(unsigned char bit)
 	unsigned char val;
 	int ret;
 
+	/* if the bit is set, return from here */
+	if (rtc_irq_bits & bit)
+		return 0;
+
 	val = rtc_irq_bits | bit;
 	val &= ~BIT_RTC_INTERRUPTS_REG_EVERY_M;
 	ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG);
@@ -193,6 +197,10 @@ static int mask_rtc_irq_bit(unsigned char bit)
 	unsigned char val;
 	int ret;
 
+	/* if the bit is clear, return from here */
+	if (!(rtc_irq_bits & bit))
+		return 0;
+
 	val = rtc_irq_bits & ~bit;
 	ret = twl_rtc_write_u8(val, REG_RTC_INTERRUPTS_REG);
 	if (ret == 0)