mtd: implement common reboot notifier boilerplate

cfi_cmdset_000{1,2}.c already implement their own reboot notifiers, and
we're going to add one for NAND. Let's put the boilerplate in one place.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Scott Branden <sbranden@broadcom.com>

drivers/mtd/mtdcore.c

@@ -37,6 +37,7 @@
 #include <linux/backing-dev.h>
 #include <linux/gfp.h>
 #include <linux/slab.h>
+#include <linux/reboot.h>
 
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
@@ -365,6 +366,17 @@ static struct device_type mtd_devtype = {
 	.release	= mtd_release,
 };
 
+static int mtd_reboot_notifier(struct notifier_block *n, unsigned long state,
+			       void *cmd)
+{
+	struct mtd_info *mtd;
+
+	mtd = container_of(n, struct mtd_info, reboot_notifier);
+	mtd->_reboot(mtd);
+
+	return NOTIFY_DONE;
+}
+
 /**
  *	add_mtd_device - register an MTD device
  *	@mtd: pointer to new MTD device info structure
@@ -565,6 +577,11 @@ int mtd_device_parse_register(struct mtd_info *mtd, const char * const *types,
 			err = -ENODEV;
 	}
 
+	if (mtd->_reboot) {
+		mtd->reboot_notifier.notifier_call = mtd_reboot_notifier;
+		register_reboot_notifier(&mtd->reboot_notifier);
+	}
+
 	return err;
 }
 EXPORT_SYMBOL_GPL(mtd_device_parse_register);
@@ -579,6 +596,9 @@ int mtd_device_unregister(struct mtd_info *master)
 {
 	int err;
 
+	if (master->_reboot)
+		unregister_reboot_notifier(&master->reboot_notifier);
+
 	err = del_mtd_partitions(master);
 	if (err)
 		return err;

include/linux/mtd/mtd.h

@@ -227,6 +227,7 @@ struct mtd_info {
 	int (*_block_markbad) (struct mtd_info *mtd, loff_t ofs);
 	int (*_suspend) (struct mtd_info *mtd);
 	void (*_resume) (struct mtd_info *mtd);
+	void (*_reboot) (struct mtd_info *mtd);
 	/*
 	 * If the driver is something smart, like UBI, it may need to maintain
 	 * its own reference counting. The below functions are only for driver.