2 files changed, 19 insertions, 8 deletions

diff --git a/Documentation/rtc.txt b/Documentation/rtc.txt
index 32aa4002de4a..596b60c08b74 100644
--- a/Documentation/rtc.txt
+++ b/Documentation/rtc.txt
@@ -153,9 +153,10 @@ since_epoch:	 The number of seconds since the epoch according to the RTC
 time:            RTC-provided time
 wakealarm:       The time at which the clock will generate a system wakeup
                  event. This is a one shot wakeup event, so must be reset
-                 after wake if a daily wakeup is required. Format is either
-                 seconds since the epoch or, if there's a leading +, seconds
-                 in the future.
+                 after wake if a daily wakeup is required. Format is seconds since
+                 the epoch by default, or if there's a leading +, seconds in the
+                 future, or if there is a leading +=, seconds ahead of the current
+                 alarm.
 
 IOCTL INTERFACE
 ---------------
diff --git a/drivers/rtc/rtc-sysfs.c b/drivers/rtc/rtc-sysfs.c
index b70e2bb63645..4b26f8672b2d 100644
--- a/drivers/rtc/rtc-sysfs.c
+++ b/drivers/rtc/rtc-sysfs.c
@@ -164,6 +164,7 @@ rtc_sysfs_set_wakealarm(struct device *dev, struct device_attribute *attr,
 {
         ssize_t retval;
         unsigned long now, alarm;
+        unsigned long push = 0;
         struct rtc_wkalrm alm;
         struct rtc_device *rtc = to_rtc_device(dev);
         char *buf_ptr;
@@ -180,13 +181,17 @@ rtc_sysfs_set_wakealarm(struct device *dev, struct device_attribute *attr,
         buf_ptr = (char *)buf;
         if (*buf_ptr == '+') {
                 buf_ptr++;
-                adjust = 1;
+                if (*buf_ptr == '=') {
+                        buf_ptr++;
+                        push = 1;
+                } else
+                        adjust = 1;
         }
         alarm = simple_strtoul(buf_ptr, NULL, 0);
         if (adjust) {
                 alarm += now;
         }
-        if (alarm > now) {
+        if (alarm > now || push) {
                 /* Avoid accidentally clobbering active alarms; we can't
                  * entirely prevent that here, without even the minimal
                  * locking from the /dev/rtcN api.
@@ -194,9 +199,14 @@ rtc_sysfs_set_wakealarm(struct device *dev, struct device_attribute *attr,
                 retval = rtc_read_alarm(rtc, &alm);
                 if (retval < 0)
                         return retval;
-                if (alm.enabled)
-                        return -EBUSY;
-
+                if (alm.enabled) {
+                        if (push) {
+                                rtc_tm_to_time(&alm.time, &push);
+                                alarm += push;
+                        } else
+                                return -EBUSY;
+                } else if (push)
+                        return -EINVAL;
                 alm.enabled = 1;
         } else {
                 alm.enabled = 0;