alarmtimer: Make alarmtimer platform device child of RTC device

The alarmtimer_suspend() function will fail if an RTC device is on a bus
such as SPI or i2c and that RTC device registers and probes after
alarmtimer_init() registers and probes the 'alarmtimer' platform device.

This is because system wide suspend suspends devices in the reverse order
of their probe. When alarmtimer_suspend() attempts to program the RTC for a
wakeup it will try to program an RTC device on a bus that has already been
suspended.

Move the alarmtimer device registration to happen when the RTC which is
used for wakeup is registered. Register the 'alarmtimer' platform device as
a child of the RTC device too, so that it can be guaranteed that the RTC
device won't be suspended when alarmtimer_suspend() is called.
Reported-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20200124055849.154411-2-swboyd@chromium.org

kernel/time/alarmtimer.c

@@ -89,6 +89,7 @@ static int alarmtimer_rtc_add_device(struct device *dev,
 	unsigned long flags;
 	struct rtc_device *rtc = to_rtc_device(dev);
 	struct wakeup_source *__ws;
+	struct platform_device *pdev;
 	int ret = 0;
 
 	if (rtcdev)
@@ -100,9 +101,11 @@ static int alarmtimer_rtc_add_device(struct device *dev,
 		return -1;
 
 	__ws = wakeup_source_register(dev, "alarmtimer");
+	pdev = platform_device_register_data(dev, "alarmtimer",
+					     PLATFORM_DEVID_AUTO, NULL, 0);
 
 	spin_lock_irqsave(&rtcdev_lock, flags);
-	if (!rtcdev) {
+	if (__ws && !IS_ERR(pdev) && !rtcdev) {
 		if (!try_module_get(rtc->owner)) {
 			ret = -1;
 			goto unlock;
@@ -113,10 +116,14 @@ static int alarmtimer_rtc_add_device(struct device *dev,
 		get_device(dev);
 		ws = __ws;
 		__ws = NULL;
+		pdev = NULL;
+	} else {
+		ret = -1;
 	}
 unlock:
 	spin_unlock_irqrestore(&rtcdev_lock, flags);
 
+	platform_device_unregister(pdev);
 	wakeup_source_unregister(__ws);
 
 	return ret;
@@ -903,8 +910,7 @@ static void get_boottime_timespec(struct timespec64 *tp)
  */
 static int __init alarmtimer_init(void)
 {
-	struct platform_device *pdev;
-	int error = 0;
+	int error;
 	int i;
 
 	alarmtimer_rtc_timer_init();
@@ -929,15 +935,7 @@ static int __init alarmtimer_init(void)
 	if (error)
 		goto out_if;
 
-	pdev = platform_device_register_simple("alarmtimer", -1, NULL, 0);
-	if (IS_ERR(pdev)) {
-		error = PTR_ERR(pdev);
-		goto out_drv;
-	}
 	return 0;
-
-out_drv:
-	platform_driver_unregister(&alarmtimer_driver);
 out_if:
 	alarmtimer_rtc_interface_remove();
 	return error;