mtd: nand: fix nand_lock/unlock() function

Do nand reset before write protect check.

If we want to check the WP# low or high through STATUS READ and check bit 7,
we must reset the device, other operation (eg.erase/program a locked block) can
also clear the bit 7 of status register.

As we know the status register can be refreshed, if we do some operation to trigger it,
for example if we do erase/program operation to one block that is locked, then READ STATUS,
the bit 7 of READ STATUS will be 0 indicate the device in write protect, then if we do
erase/program operation to another block that is unlocked, the bit 7 of READ STATUS will
be 1 indicate the device is not write protect.
Suppose we checked the bit 7 of READ STATUS is 0 then judge the WP# is low (write protect),
but in this case the WP# maybe high if we do erase/program operation to a locked block,
so we must reset the device if we want to check the WP# low or high through STATUS READ and
check bit 7.
Signed-off-by: White Ding <bpqw@micron.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/nand_base.c

@@ -982,6 +982,15 @@ int nand_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
 
 	chip->select_chip(mtd, chipnr);
 
+	/*
+	 * Reset the chip.
+	 * If we want to check the WP through READ STATUS and check the bit 7
+	 * we must reset the chip
+	 * some operation can also clear the bit 7 of status register
+	 * eg. erase/program a locked block
+	 */
+	chip->cmdfunc(mtd, NAND_CMD_RESET, -1, -1);
+
 	/* Check, if it is write protected */
 	if (nand_check_wp(mtd)) {
 		pr_debug("%s: device is write protected!\n",
@@ -1032,6 +1041,15 @@ int nand_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
 
 	chip->select_chip(mtd, chipnr);
 
+	/*
+	 * Reset the chip.
+	 * If we want to check the WP through READ STATUS and check the bit 7
+	 * we must reset the chip
+	 * some operation can also clear the bit 7 of status register
+	 * eg. erase/program a locked block
+	 */
+	chip->cmdfunc(mtd, NAND_CMD_RESET, -1, -1);
+
 	/* Check, if it is write protected */
 	if (nand_check_wp(mtd)) {
 		pr_debug("%s: device is write protected!\n",