mtd: add OTP (one-time-programmable) erase ioctl

This may sound like a contradiction but some SPI-NOR flashes really
support erasing their OTP region until it is finally locked. Having the
possibility to erase an OTP region might come in handy during
development.

The ioctl argument follows the OTPLOCK style.
Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210303201819.2752-1-michael@walle.cc

drivers/mtd/mtdchar.c

@@ -666,6 +666,7 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 	case MEMWRITEOOB64:
 	case MEMWRITE:
 	case OTPLOCK:
+	case OTPERASE:
 		if (!(file->f_mode & FMODE_WRITE))
 			return -EPERM;
 		break;
@@ -930,6 +931,7 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 	}
 
 	case OTPLOCK:
+	case OTPERASE:
 	{
 		struct otp_info oinfo;
 
@@ -937,7 +939,10 @@ static int mtdchar_ioctl(struct file *file, u_int cmd, u_long arg)
 			return -EINVAL;
 		if (copy_from_user(&oinfo, argp, sizeof(oinfo)))
 			return -EFAULT;
-		ret = mtd_lock_user_prot_reg(mtd, oinfo.start, oinfo.length);
+		if (cmd == OTPLOCK)
+			ret = mtd_lock_user_prot_reg(mtd, oinfo.start, oinfo.length);
+		else
+			ret = mtd_erase_user_prot_reg(mtd, oinfo.start, oinfo.length);
 		break;
 	}
 

drivers/mtd/mtdcore.c

@@ -1919,6 +1919,18 @@ int mtd_lock_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len)
 }
 EXPORT_SYMBOL_GPL(mtd_lock_user_prot_reg);
 
+int mtd_erase_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len)
+{
+	struct mtd_info *master = mtd_get_master(mtd);
+
+	if (!master->_erase_user_prot_reg)
+		return -EOPNOTSUPP;
+	if (!len)
+		return 0;
+	return master->_erase_user_prot_reg(master, from, len);
+}
+EXPORT_SYMBOL_GPL(mtd_erase_user_prot_reg);
+
 /* Chip-supported device locking */
 int mtd_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len)
 {

include/linux/mtd/mtd.h

@@ -337,6 +337,8 @@ struct mtd_info {
 				     size_t len, size_t *retlen, u_char *buf);
 	int (*_lock_user_prot_reg) (struct mtd_info *mtd, loff_t from,
 				    size_t len);
+	int (*_erase_user_prot_reg) (struct mtd_info *mtd, loff_t from,
+				     size_t len);
 	int (*_writev) (struct mtd_info *mtd, const struct kvec *vecs,
 			unsigned long count, loff_t to, size_t *retlen);
 	void (*_sync) (struct mtd_info *mtd);
@@ -518,6 +520,7 @@ int mtd_read_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len,
 int mtd_write_user_prot_reg(struct mtd_info *mtd, loff_t to, size_t len,
 			    size_t *retlen, u_char *buf);
 int mtd_lock_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len);
+int mtd_erase_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len);
 
 int mtd_writev(struct mtd_info *mtd, const struct kvec *vecs,
 	       unsigned long count, loff_t to, size_t *retlen);

include/uapi/mtd/mtd-abi.h

@@ -205,6 +205,8 @@ struct otp_info {
  * without OOB, e.g., NOR flash.
  */
 #define MEMWRITE		_IOWR('M', 24, struct mtd_write_req)
+/* Erase a given range of user data (must be in mode %MTD_FILE_MODE_OTP_USER) */
+#define OTPERASE		_IOW('M', 25, struct otp_info)
 
 /*
  * Obsolete legacy interface. Keep it in order not to break userspace