rtc: class: make rtc_class constant

Since commit 43a7206b ("driver core: class: make class_register() take
a const *"), the driver core allows for struct class to be in read-only
memory, so move the rtc_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at boot time.

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ricardo B. Marliere <ricardo@marliere.net>
Link: https://lore.kernel.org/r/20240305-class_cleanup-abelloni-v1-1-944c026137c8@marliere.netSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/rtc/class.c

@@ -21,7 +21,6 @@
 #include "rtc-core.h"
 
 static DEFINE_IDA(rtc_ida);
-struct class *rtc_class;
 
 static void rtc_device_release(struct device *dev)
 {
@@ -199,6 +198,11 @@ static SIMPLE_DEV_PM_OPS(rtc_class_dev_pm_ops, rtc_suspend, rtc_resume);
 #define RTC_CLASS_DEV_PM_OPS	NULL
 #endif
 
+const struct class rtc_class = {
+	.name = "rtc",
+	.pm = RTC_CLASS_DEV_PM_OPS,
+};
+
 /* Ensure the caller will set the id before releasing the device */
 static struct rtc_device *rtc_allocate_device(void)
 {
@@ -220,7 +224,7 @@ static struct rtc_device *rtc_allocate_device(void)
 
 	rtc->irq_freq = 1;
 	rtc->max_user_freq = 64;
-	rtc->dev.class = rtc_class;
+	rtc->dev.class = &rtc_class;
 	rtc->dev.groups = rtc_get_dev_attribute_groups();
 	rtc->dev.release = rtc_device_release;
 
@@ -475,13 +479,14 @@ EXPORT_SYMBOL_GPL(devm_rtc_device_register);
 
 static int __init rtc_init(void)
 {
-	rtc_class = class_create("rtc");
-	if (IS_ERR(rtc_class)) {
-		pr_err("couldn't create class\n");
-		return PTR_ERR(rtc_class);
-	}
-	rtc_class->pm = RTC_CLASS_DEV_PM_OPS;
+	int err;
+
+	err = class_register(&rtc_class);
+	if (err)
+		return err;
+
 	rtc_dev_init();
+
 	return 0;
 }
 subsys_initcall(rtc_init);

drivers/rtc/interface.c

@@ -696,7 +696,7 @@ struct rtc_device *rtc_class_open(const char *name)
 	struct device *dev;
 	struct rtc_device *rtc = NULL;
 
-	dev = class_find_device_by_name(rtc_class, name);
+	dev = class_find_device_by_name(&rtc_class, name);
 	if (dev)
 		rtc = to_rtc_device(dev);
 

include/linux/rtc.h

@@ -42,7 +42,7 @@ static inline time64_t rtc_tm_sub(struct rtc_time *lhs, struct rtc_time *rhs)
 #include <linux/timerqueue.h>
 #include <linux/workqueue.h>
 
-extern struct class *rtc_class;
+extern const struct class rtc_class;
 
 /*
  * For these RTC methods the device parameter is the physical device

kernel/power/suspend_test.c

@@ -201,7 +201,7 @@ static int __init test_suspend(void)
 	}
 
 	/* RTCs have initialized by now too ... can we use one? */
-	dev = class_find_device(rtc_class, NULL, NULL, has_wakealarm);
+	dev = class_find_device(&rtc_class, NULL, NULL, has_wakealarm);
 	if (dev) {
 		rtc = rtc_class_open(dev_name(dev));
 		put_device(dev);

kernel/time/alarmtimer.c

@@ -134,7 +134,7 @@ static struct class_interface alarmtimer_rtc_interface = {
 
 static int alarmtimer_rtc_interface_setup(void)
 {
-	alarmtimer_rtc_interface.class = rtc_class;
+	alarmtimer_rtc_interface.class = &rtc_class;
 	return class_interface_register(&alarmtimer_rtc_interface);
 }
 static void alarmtimer_rtc_interface_remove(void)