RPMSG_DEV_MAX
ret = ida_alloc_max(&rpmsg_minor_ida, RPMSG_DEV_MAX - 1, GFP_KERNEL);
ret = alloc_chrdev_region(&rpmsg_major, 0, RPMSG_DEV_MAX, "rpmsg_char");
unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
ret = ida_alloc_max(&rpmsg_minor_ida, RPMSG_DEV_MAX - 1, GFP_KERNEL);
ret = alloc_chrdev_region(&rpmsg_major, 0, RPMSG_DEV_MAX, "rpmsg_ctrl");
unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);
unregister_chrdev_region(rpmsg_major, RPMSG_DEV_MAX);