/dev/mem: make mem_class a static const structure

Now that the driver core allows for struct class to be in read-only
memory, move the mem_class structure to be declared at build time
placing it into read-only memory, instead of having to be dynamically
allocated at load time.

Cc: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ivan Orlov <ivan.orlov0322@gmail.com>
Link: https://lore.kernel.org/r/20230620143751.578239-13-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ivanorlov2206

drivers/char/mem.c

@@ -753,20 +753,23 @@ static char *mem_devnode(const struct device *dev, umode_t *mode)
 	return NULL;
 }
 
-static struct class *mem_class;
+static const struct class mem_class = {
+	.name		= "mem",
+	.devnode	= mem_devnode,
+};
 
 static int __init chr_dev_init(void)
 {
+	int retval;
 	int minor;
 
 	if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
 		printk("unable to get major %d for memory devs\n", MEM_MAJOR);
 
-	mem_class = class_create("mem");
-	if (IS_ERR(mem_class))
-		return PTR_ERR(mem_class);
+	retval = class_register(&mem_class);
+	if (retval)
+		return retval;
 
-	mem_class->devnode = mem_devnode;
 	for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
 		if (!devlist[minor].name)
 			continue;
@@ -777,7 +780,7 @@ static int __init chr_dev_init(void)
 		if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
 			continue;
 
-		device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
+		device_create(&mem_class, NULL, MKDEV(MEM_MAJOR, minor),
 			      NULL, devlist[minor].name);
 	}