rtc: cmos: Cancel alarm timer if alarm time is equal to now+1 seconds

Steps to reproduce the problem:
	1) Enable RTC wake-up option in BIOS Setup
	2) Issue one of these commands in the OS: "poweroff"
	   or "shutdown -h now"
	3) System will shut down and then reboot automatically

Root-cause of the issue:
	1) During the shutdown process, the hwclock utility is used
	   to save the system clock to hardware clock (RTC).
	2) The hwclock utility invokes ioctl() with RTC_UIE_ON. The
	   kernel configures the RTC alarm for the periodic interrupt
	   (every 1 second).
	3) The hwclock uitlity closes the /dev/rtc0 device, and the
	   kernel disables the RTC alarm irq (AIE bit of Register B)
	   via ioctl() with RTC_UIE_OFF. But, the configured alarm
	   time is the current_time + 1.
	4) After the next 1 second is elapsed, the AF (alarm
	   interrupt flag) of Register C is set.
	5) The S5 handler in BIOS is invoked to configure alarm
	   registers (enable AIE bit and configure alarm date/time).
	   But, BIOS does not clear the previous interrupt status
	   during alarm configuration. Therefore, "AF=AIE=1" causes
	   the rtc device to trigger an interrupt.
	6) So, the machine reboots automatically right after shutdown.

This patch cancels the alarm timer if the following condictions are
met (suggested by Alexandre):
	1) The configured alarm time is equal to current_time + 1
	   seconds.
	2) The AIE timer is not in use.

The member 'alarm_expires' is introduced in struct cmos_rtc because
of the following reasons:
	1) The configured alarm time can be retrieved from
	   cmos_read_alarm(), but we need to take the 'wrapped
	   timestamp' and 'time rollover' into consideration. The
	   function __rtc_read_alarm() eliminates the concerns. To
	   avoid the duplicated code in the lower level RTC driver,
	   invoking __rtc_read_alarm from the lower level RTC driver
	   is not encouraged. Moreover, the compilation error 'the
	   undefined __rtc_read_alarm" is observed if the lower level
	   RTC driver is compiled as a kernel module.
	2) The uie_rtctimer.node.expires and aie_timer.node.expires can
	   be retrieved for the configured alarm time. But, the problem
	   is that either of them might configure the CMOS alarm time.
	   We cannot make sure UIE timer or AIE tiemr configured the
	   CMOS alarm time before. (uie_rtctimer or aie_timer is enabled
	   and then is disabled).
	3) The patch introduces the member 'alarm_expires' to keep the
	   newly configured alarm time, so the above-mentioned concerns
	   can be eliminated.

The issue goes away after 20-time shutdown tests.
Signed-off-by: Adrian Huang <ahuang12@lenovo.com>
Tested-by: Egbert Eich <eich@suse.de>
Tested-by: Diego Ercolani <diego.ercolani@gmail.com>
Cc: Borislav Petkov <bp@suse.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-cmos.c

@@ -51,6 +51,7 @@ struct cmos_rtc {
 	struct device		*dev;
 	int			irq;
 	struct resource		*iomem;
+	time64_t		alarm_expires;
 
 	void			(*wake_on)(struct device *);
 	void			(*wake_off)(struct device *);
@@ -377,6 +378,8 @@ static int cmos_set_alarm(struct device *dev, struct rtc_wkalrm *t)
 
 	spin_unlock_irq(&rtc_lock);
 
+	cmos->alarm_expires = rtc_tm_to_time64(&t->time);
+
 	return 0;
 }
 
@@ -860,6 +863,51 @@ static void __exit cmos_do_remove(struct device *dev)
 	cmos->dev = NULL;
 }
 
+static int cmos_aie_poweroff(struct device *dev)
+{
+	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
+	struct rtc_time now;
+	time64_t t_now;
+	int retval = 0;
+	unsigned char rtc_control;
+
+	if (!cmos->alarm_expires)
+		return -EINVAL;
+
+	spin_lock_irq(&rtc_lock);
+	rtc_control = CMOS_READ(RTC_CONTROL);
+	spin_unlock_irq(&rtc_lock);
+
+	/* We only care about the situation where AIE is disabled. */
+	if (rtc_control & RTC_AIE)
+		return -EBUSY;
+
+	cmos_read_time(dev, &now);
+	t_now = rtc_tm_to_time64(&now);
+
+	/*
+	 * When enabling "RTC wake-up" in BIOS setup, the machine reboots
+	 * automatically right after shutdown on some buggy boxes.
+	 * This automatic rebooting issue won't happen when the alarm
+	 * time is larger than now+1 seconds.
+	 *
+	 * If the alarm time is equal to now+1 seconds, the issue can be
+	 * prevented by cancelling the alarm.
+	 */
+	if (cmos->alarm_expires == t_now + 1) {
+		struct rtc_wkalrm alarm;
+
+		/* Cancel the AIE timer by configuring the past time. */
+		rtc_time64_to_tm(t_now - 1, &alarm.time);
+		alarm.enabled = 0;
+		retval = cmos_set_alarm(dev, &alarm);
+	} else if (cmos->alarm_expires > t_now + 1) {
+		retval = -EBUSY;
+	}
+
+	return retval;
+}
+
 #ifdef CONFIG_PM
 
 static int cmos_suspend(struct device *dev)
@@ -1094,8 +1142,12 @@ static void cmos_pnp_shutdown(struct pnp_dev *pnp)
 	struct device *dev = &pnp->dev;
 	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
 
-	if (system_state == SYSTEM_POWER_OFF && !cmos_poweroff(dev))
-		return;
+	if (system_state == SYSTEM_POWER_OFF) {
+		int retval = cmos_poweroff(dev);
+
+		if (cmos_aie_poweroff(dev) < 0 && !retval)
+			return;
+	}
 
 	cmos_do_shutdown(cmos->irq);
 }
@@ -1200,8 +1252,12 @@ static void cmos_platform_shutdown(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct cmos_rtc	*cmos = dev_get_drvdata(dev);
 
-	if (system_state == SYSTEM_POWER_OFF && !cmos_poweroff(dev))
-		return;
+	if (system_state == SYSTEM_POWER_OFF) {
+		int retval = cmos_poweroff(dev);
+
+		if (cmos_aie_poweroff(dev) < 0 && !retval)
+			return;
+	}
 
 	cmos_do_shutdown(cmos->irq);
 }