rtc: sa1100: fix possible race condition

Both RTC IRQs are requested before the struct rtc_device is allocated,
this may lead to a NULL pointer dereference in the IRQ handler.

To fix this issue, allocating the rtc_device struct before requesting
the IRQs using devm_rtc_allocate_device, and use rtc_register_device
to register the RTC device.

Link: https://lore.kernel.org/r/20200306010146.39762-1-alexandre.belloni@bootlin.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-sa1100.c

@@ -182,7 +182,6 @@ static const struct rtc_class_ops sa1100_rtc_ops = {
 
 int sa1100_rtc_init(struct platform_device *pdev, struct sa1100_rtc *info)
 {
-	struct rtc_device *rtc;
 	int ret;
 
 	spin_lock_init(&info->lock);
@@ -211,15 +210,14 @@ int sa1100_rtc_init(struct platform_device *pdev, struct sa1100_rtc *info)
 		writel_relaxed(0, info->rcnr);
 	}
 
-	rtc = devm_rtc_device_register(&pdev->dev, pdev->name, &sa1100_rtc_ops,
-					THIS_MODULE);
-	if (IS_ERR(rtc)) {
+	info->rtc->ops = &sa1100_rtc_ops;
+	info->rtc->max_user_freq = RTC_FREQ;
+
+	ret = rtc_register_device(info->rtc);
+	if (ret) {
 		clk_disable_unprepare(info->clk);
-		return PTR_ERR(rtc);
+		return ret;
 	}
-	info->rtc = rtc;
-
-	rtc->max_user_freq = RTC_FREQ;
 
 	/* Fix for a nasty initialization problem the in SA11xx RTSR register.
 	 * See also the comments in sa1100_rtc_interrupt().
@@ -267,6 +265,10 @@ static int sa1100_rtc_probe(struct platform_device *pdev)
 	info->irq_1hz = irq_1hz;
 	info->irq_alarm = irq_alarm;
 
+	info->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(info->rtc))
+		return PTR_ERR(info->rtc);
+
 	ret = devm_request_irq(&pdev->dev, irq_1hz, sa1100_rtc_interrupt, 0,
 			       "rtc 1Hz", &pdev->dev);
 	if (ret) {