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rtc-cmos alarm acts as oneshot
Start making the rtc-cmos alarm act more like a oneshot alarm by disabling that alarm after its IRQ fires. (ACPI hooks are also needed.) The Linux RTC framework has previously been a bit vague in this area, but any other behavior is problematic and not very portable. RTCs with full YYYY-MM-DD HH:MM[:SS] alarms won't have a problem here. Only ones with partial match criteria, with the most visible example being the PC RTC, get confused. (Because the criteria will match repeatedly.) Update comments relating to that oneshot behavior and timezone handling. (Timezones are another issue that's mostly visible with rtc-cmos. That's because PCs often dual-boot MS-Windows, which likes its RTC to match local wall-clock time instead of UTC.) 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>
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739d340dba
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3 changed files with 35 additions and 7 deletions
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@ -472,10 +472,22 @@ static struct cmos_rtc cmos_rtc;
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static irqreturn_t cmos_interrupt(int irq, void *p)
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static irqreturn_t cmos_interrupt(int irq, void *p)
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{
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{
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u8 irqstat;
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u8 irqstat;
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u8 rtc_control;
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spin_lock(&rtc_lock);
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spin_lock(&rtc_lock);
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irqstat = CMOS_READ(RTC_INTR_FLAGS);
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irqstat = CMOS_READ(RTC_INTR_FLAGS);
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irqstat &= (CMOS_READ(RTC_CONTROL) & RTC_IRQMASK) | RTC_IRQF;
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rtc_control = CMOS_READ(RTC_CONTROL);
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irqstat &= (rtc_control & RTC_IRQMASK) | RTC_IRQF;
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/* All Linux RTC alarms should be treated as if they were oneshot.
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* Similar code may be needed in system wakeup paths, in case the
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* alarm woke the system.
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*/
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if (irqstat & RTC_AIE) {
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rtc_control &= ~RTC_AIE;
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CMOS_WRITE(rtc_control, RTC_CONTROL);
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CMOS_READ(RTC_INTR_FLAGS);
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}
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spin_unlock(&rtc_lock);
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spin_unlock(&rtc_lock);
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if (is_intr(irqstat)) {
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if (is_intr(irqstat)) {
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@ -246,6 +246,15 @@ static int rtc_dev_ioctl(struct inode *inode, struct file *file,
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/* if the driver does not provide the ioctl interface
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/* if the driver does not provide the ioctl interface
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* or if that particular ioctl was not implemented
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* or if that particular ioctl was not implemented
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* (-ENOIOCTLCMD), we will try to emulate here.
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* (-ENOIOCTLCMD), we will try to emulate here.
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*
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* Drivers *SHOULD NOT* provide ioctl implementations
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* for these requests. Instead, provide methods to
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* support the following code, so that the RTC's main
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* features are accessible without using ioctls.
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*
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* RTC and alarm times will be in UTC, by preference,
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* but dual-booting with MS-Windows implies RTCs must
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* use the local wall clock time.
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*/
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*/
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switch (cmd) {
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switch (cmd) {
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@ -17,6 +17,13 @@
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/* device attributes */
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/* device attributes */
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/*
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* NOTE: RTC times displayed in sysfs use the RTC's timezone. That's
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* ideally UTC. However, PCs that also boot to MS-Windows normally use
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* the local time and change to match daylight savings time. That affects
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* attributes including date, time, since_epoch, and wakealarm.
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*/
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static ssize_t
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static ssize_t
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rtc_sysfs_show_name(struct device *dev, struct device_attribute *attr,
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rtc_sysfs_show_name(struct device *dev, struct device_attribute *attr,
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char *buf)
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char *buf)
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@ -113,13 +120,13 @@ rtc_sysfs_show_wakealarm(struct device *dev, struct device_attribute *attr,
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unsigned long alarm;
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unsigned long alarm;
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struct rtc_wkalrm alm;
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struct rtc_wkalrm alm;
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/* Don't show disabled alarms; but the RTC could leave the
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/* Don't show disabled alarms. For uniformity, RTC alarms are
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* alarm enabled after it's already triggered. Alarms are
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* conceptually one-shot, even though some common RTCs (on PCs)
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* conceptually one-shot, even though some common hardware
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* don't actually work that way.
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* (PCs) doesn't actually work that way.
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*
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*
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* REVISIT maybe we should require RTC implementations to
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* NOTE: RTC implementations where the alarm doesn't match an
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* disable the RTC alarm after it triggers, for uniformity.
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* exact YYYY-MM-DD HH:MM[:SS] date *must* disable their RTC
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* alarms after they trigger, to ensure one-shot semantics.
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*/
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*/
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retval = rtc_read_alarm(to_rtc_device(dev), &alm);
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retval = rtc_read_alarm(to_rtc_device(dev), &alm);
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if (retval == 0 && alm.enabled) {
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if (retval == 0 && alm.enabled) {
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