rtc: utilize new cdev_device_add helper function

Mostly straightforward, but we had to remove the rtc_dev_add/del_device
functions as they split up the cdev_add and the device_add.

Doing this also revealed that there was likely another subtle bug:
seeing cdev_add was done after device_register, the cdev probably
was not ready before device_add when the uevent occurs. This would
race with userspace, if it tried to use the device directly after
the uevent. This is fixed just by using the new helper function.

Another weird thing is this driver would, in some error cases, call
cdev_add() without calling cdev_init. This patchset corrects this
by avoiding calling cdev_add if the devt is not set.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/rtc/class.c

@@ -195,6 +195,8 @@ struct rtc_device *rtc_device_register(const char *name, struct device *dev,
 		goto exit_ida;
 	}
 
+	device_initialize(&rtc->dev);
+
 	rtc->id = id;
 	rtc->ops = ops;
 	rtc->owner = owner;
@@ -233,14 +235,19 @@ struct rtc_device *rtc_device_register(const char *name, struct device *dev,
 
 	rtc_dev_prepare(rtc);
 
-	err = device_register(&rtc->dev);
+	err = cdev_device_add(&rtc->char_dev, &rtc->dev);
 	if (err) {
+		dev_warn(&rtc->dev, "%s: failed to add char device %d:%d\n",
+			 rtc->name, MAJOR(rtc->dev.devt), rtc->id);
+
 		/* This will free both memory and the ID */
 		put_device(&rtc->dev);
 		goto exit;
+	} else {
+		dev_dbg(&rtc->dev, "%s: dev (%d:%d)\n", rtc->name,
+			MAJOR(rtc->dev.devt), rtc->id);
 	}
 
-	rtc_dev_add_device(rtc);
 	rtc_proc_add_device(rtc);
 
 	dev_info(dev, "rtc core: registered %s as %s\n",
@@ -271,9 +278,8 @@ void rtc_device_unregister(struct rtc_device *rtc)
 	 * Remove innards of this RTC, then disable it, before
 	 * letting any rtc_class_open() users access it again
 	 */
-	rtc_dev_del_device(rtc);
 	rtc_proc_del_device(rtc);
-	device_del(&rtc->dev);
+	cdev_device_del(&rtc->char_dev, &rtc->dev);
 	rtc->ops = NULL;
 	mutex_unlock(&rtc->ops_lock);
 	put_device(&rtc->dev);

drivers/rtc/rtc-core.h

@@ -3,8 +3,6 @@
 extern void __init rtc_dev_init(void);
 extern void __exit rtc_dev_exit(void);
 extern void rtc_dev_prepare(struct rtc_device *rtc);
-extern void rtc_dev_add_device(struct rtc_device *rtc);
-extern void rtc_dev_del_device(struct rtc_device *rtc);
 
 #else
 
@@ -20,14 +18,6 @@ static inline void rtc_dev_prepare(struct rtc_device *rtc)
 {
 }
 
-static inline void rtc_dev_add_device(struct rtc_device *rtc)
-{
-}
-
-static inline void rtc_dev_del_device(struct rtc_device *rtc)
-{
-}
-
 #endif
 
 #ifdef CONFIG_RTC_INTF_PROC

drivers/rtc/rtc-dev.c

@@ -477,23 +477,6 @@ void rtc_dev_prepare(struct rtc_device *rtc)
 
 	cdev_init(&rtc->char_dev, &rtc_dev_fops);
 	rtc->char_dev.owner = rtc->owner;
-	rtc->char_dev.kobj.parent = &rtc->dev.kobj;
-}
-
-void rtc_dev_add_device(struct rtc_device *rtc)
-{
-	if (cdev_add(&rtc->char_dev, rtc->dev.devt, 1))
-		dev_warn(&rtc->dev, "%s: failed to add char device %d:%d\n",
-			rtc->name, MAJOR(rtc_devt), rtc->id);
-	else
-		dev_dbg(&rtc->dev, "%s: dev (%d:%d)\n", rtc->name,
-			MAJOR(rtc_devt), rtc->id);
-}
-
-void rtc_dev_del_device(struct rtc_device *rtc)
-{
-	if (rtc->dev.devt)
-		cdev_del(&rtc->char_dev);
 }
 
 void __init rtc_dev_init(void)