rtc: sunxi: fix possible race condition

The IRQ is requested before the struct rtc is allocated and registered, but
this struct is used in the IRQ handler. This may lead to a NULL pointer
dereference.

Switch to devm_rtc_allocate_device/rtc_register_device to allocate the rtc
before requesting the IRQ.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/rtc-sunxi.c

@@ -445,6 +445,10 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, chip);
 	chip->dev = &pdev->dev;
 
+	chip->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(chip->rtc))
+		return PTR_ERR(chip->rtc);
+
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	chip->base = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(chip->base))
@@ -481,30 +485,21 @@ static int sunxi_rtc_probe(struct platform_device *pdev)
 	writel(SUNXI_ALRM_IRQ_STA_CNT_IRQ_PEND, chip->base +
 			SUNXI_ALRM_IRQ_STA);
 
-	chip->rtc = rtc_device_register("rtc-sunxi", &pdev->dev,
-			&sunxi_rtc_ops, THIS_MODULE);
-	if (IS_ERR(chip->rtc)) {
+	chip->rtc->ops = &sunxi_rtc_ops;
+
+	ret = rtc_register_device(chip->rtc);
+	if (ret) {
 		dev_err(&pdev->dev, "unable to register device\n");
-		return PTR_ERR(chip->rtc);
+		return ret;
 	}
 
 	dev_info(&pdev->dev, "RTC enabled\n");
 
 	return 0;
 }
 
-static int sunxi_rtc_remove(struct platform_device *pdev)
-{
-	struct sunxi_rtc_dev *chip = platform_get_drvdata(pdev);
-
-	rtc_device_unregister(chip->rtc);
-
-	return 0;
-}
-
 static struct platform_driver sunxi_rtc_driver = {
 	.probe		= sunxi_rtc_probe,
-	.remove		= sunxi_rtc_remove,
 	.driver		= {
 		.name		= "sunxi-rtc",
 		.of_match_table = sunxi_rtc_dt_ids,