rtc_irq_set_freq() requires power-of-two and associated kerneldoc

RTC periodic IRQs are only defined to work for 2^N Hz values.  This patch
moves that validity check into the infrastructure, so drivers don't need to
check it; and adds kerneldoc for the two interface functions related to
periodic IRQs.  (One of which was quite mysterious until its first use was
recently checked in!)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
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>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/rtc/rtc-cmos.c b/drivers/rtc/rtc-cmos.c
index 5d760bb6c2cd..6d0c35397b49 100644
--- a/drivers/rtc/rtc-cmos.c
+++ b/drivers/rtc/rtc-cmos.c
@@ -246,11 +246,9 @@ static int cmos_irq_set_freq(struct device *dev, int freq)
 
         /* 0 = no irqs; 1 = 2^15 Hz ... 15 = 2^0 Hz */
         f = ffs(freq);
-        if (f != 0) {
-                if (f-- > 16 || freq != (1 << f))
-                        return -EINVAL;
-                f = 16 - f;
-        }
+        if (f-- > 16)
+                return -EINVAL;
+        f = 16 - f;
 
         spin_lock_irqsave(&rtc_lock, flags);
         CMOS_WRITE(RTC_REF_CLCK_32KHZ | f, RTC_FREQ_SELECT);