---

yaml
---
r: 83529
b: refs/heads/master
c: 8a0bdfd
h: refs/heads/master
i:
  83527: 53053bf
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 739d340dba45ab786a5553144bbffbee0afe15dd
+refs/heads/master: 8a0bdfd7a05f5bb0486fbe7146a2cf775957e95e

trunk/drivers/rtc/rtc-cmos.c

@@ -472,10 +472,22 @@ static struct cmos_rtc	cmos_rtc;
 static irqreturn_t cmos_interrupt(int irq, void *p)
 {
 	u8		irqstat;
+	u8		rtc_control;
 
 	spin_lock(&rtc_lock);
 	irqstat = CMOS_READ(RTC_INTR_FLAGS);
-	irqstat &= (CMOS_READ(RTC_CONTROL) & RTC_IRQMASK) | RTC_IRQF;
+	rtc_control = CMOS_READ(RTC_CONTROL);
+	irqstat &= (rtc_control & RTC_IRQMASK) | RTC_IRQF;
+
+	/* All Linux RTC alarms should be treated as if they were oneshot.
+	 * Similar code may be needed in system wakeup paths, in case the
+	 * alarm woke the system.
+	 */
+	if (irqstat & RTC_AIE) {
+		rtc_control &= ~RTC_AIE;
+		CMOS_WRITE(rtc_control, RTC_CONTROL);
+		CMOS_READ(RTC_INTR_FLAGS);
+	}
 	spin_unlock(&rtc_lock);
 
 	if (is_intr(irqstat)) {

trunk/drivers/rtc/rtc-dev.c

@@ -246,6 +246,15 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
 	/* if the driver does not provide the ioctl interface
 	 * or if that particular ioctl was not implemented
 	 * (-ENOIOCTLCMD), we will try to emulate here.
+	 *
+	 * Drivers *SHOULD NOT* provide ioctl implementations
+	 * for these requests.  Instead, provide methods to
+	 * support the following code, so that the RTC's main
+	 * features are accessible without using ioctls.
+	 *
+	 * RTC and alarm times will be in UTC, by preference,
+	 * but dual-booting with MS-Windows implies RTCs must
+	 * use the local wall clock time.
 	 */
 
 	switch (cmd) {

trunk/drivers/rtc/rtc-sysfs.c

@@ -17,6 +17,13 @@
 
 /* device attributes */
 
+/*
+ * NOTE:  RTC times displayed in sysfs use the RTC's timezone.  That's
+ * ideally UTC.  However, PCs that also boot to MS-Windows normally use
+ * the local time and change to match daylight savings time.  That affects
+ * attributes including date, time, since_epoch, and wakealarm.
+ */
+
 static ssize_t
 rtc_sysfs_show_name(struct device *dev, struct device_attribute *attr,
 		char *buf)
@@ -113,13 +120,13 @@ rtc_sysfs_show_wakealarm(struct device *dev, struct device_attribute *attr,
 	unsigned long alarm;
 	struct rtc_wkalrm alm;
 
-	/* Don't show disabled alarms; but the RTC could leave the
-	 * alarm enabled after it's already triggered.  Alarms are
-	 * conceptually one-shot, even though some common hardware
-	 * (PCs) doesn't actually work that way.
+	/* Don't show disabled alarms.  For uniformity, RTC alarms are
+	 * conceptually one-shot, even though some common RTCs (on PCs)
+	 * don't actually work that way.
 	 *
-	 * REVISIT maybe we should require RTC implementations to
-	 * disable the RTC alarm after it triggers, for uniformity.
+	 * NOTE: RTC implementations where the alarm doesn't match an
+	 * exact YYYY-MM-DD HH:MM[:SS] date *must* disable their RTC
+	 * alarms after they trigger, to ensure one-shot semantics.
 	 */
 	retval = rtc_read_alarm(to_rtc_device(dev), &alm);
 	if (retval == 0 && alm.enabled) {