mtd: core: Constify buf in mtd_write_user_prot_reg()

The write buffer comes from user and should be const.
Constify write buffer in mtd core and across all _write_user_prot_reg()
users. cfi_cmdset_{0001, 0002} and onenand_base will pay the cost of an
explicit cast to discard the const qualifier since the beginning, since
they are using an otp_op_t function prototype that is used for both reads
and writes. mtd_dataflash and SPI NOR will benefit of the const buffer
because they are using different paths for writes and reads.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210403060931.7119-1-tudor.ambarus@microchip.com

drivers/mtd/chips/cfi_cmdset_0001.c

@@ -72,7 +72,8 @@ static int cfi_intelext_is_locked(struct mtd_info *mtd, loff_t ofs,
 #ifdef CONFIG_MTD_OTP
 static int cfi_intelext_read_fact_prot_reg (struct mtd_info *, loff_t, size_t, size_t *, u_char *);
 static int cfi_intelext_read_user_prot_reg (struct mtd_info *, loff_t, size_t, size_t *, u_char *);
-static int cfi_intelext_write_user_prot_reg (struct mtd_info *, loff_t, size_t, size_t *, u_char *);
+static int cfi_intelext_write_user_prot_reg(struct mtd_info *, loff_t, size_t,
+					    size_t *, const u_char *);
 static int cfi_intelext_lock_user_prot_reg (struct mtd_info *, loff_t, size_t);
 static int cfi_intelext_get_fact_prot_info(struct mtd_info *, size_t,
 					   size_t *, struct otp_info *);
@@ -2447,10 +2448,10 @@ static int cfi_intelext_read_user_prot_reg(struct mtd_info *mtd, loff_t from,
 
 static int cfi_intelext_write_user_prot_reg(struct mtd_info *mtd, loff_t from,
 					    size_t len, size_t *retlen,
-					     u_char *buf)
+					    const u_char *buf)
 {
 	return cfi_intelext_otp_walk(mtd, from, len, retlen,
-				     buf, do_otp_write, 1);
+				     (u_char *)buf, do_otp_write, 1);
 }
 
 static int cfi_intelext_lock_user_prot_reg(struct mtd_info *mtd,

drivers/mtd/chips/cfi_cmdset_0002.c

@@ -80,7 +80,7 @@ static int cfi_amdstd_read_fact_prot_reg(struct mtd_info *, loff_t, size_t,
 static int cfi_amdstd_read_user_prot_reg(struct mtd_info *, loff_t, size_t,
 					 size_t *, u_char *);
 static int cfi_amdstd_write_user_prot_reg(struct mtd_info *, loff_t, size_t,
-					  size_t *, u_char *);
+					  size_t *, const u_char *);
 static int cfi_amdstd_lock_user_prot_reg(struct mtd_info *, loff_t, size_t);
 
 static int cfi_amdstd_panic_write(struct mtd_info *mtd, loff_t to, size_t len,
@@ -1635,9 +1635,9 @@ static int cfi_amdstd_read_user_prot_reg(struct mtd_info *mtd, loff_t from,
 
 static int cfi_amdstd_write_user_prot_reg(struct mtd_info *mtd, loff_t from,
 					  size_t len, size_t *retlen,
-					  u_char *buf)
+					  const u_char *buf)
 {
-	return cfi_amdstd_otp_walk(mtd, from, len, retlen, buf,
+	return cfi_amdstd_otp_walk(mtd, from, len, retlen, (u_char *)buf,
 				   do_otp_write, 1);
 }
 

drivers/mtd/devices/mtd_dataflash.c

@@ -527,7 +527,7 @@ static int dataflash_read_user_otp(struct mtd_info *mtd,
 }
 
 static int dataflash_write_user_otp(struct mtd_info *mtd,
-		loff_t from, size_t len, size_t *retlen, u_char *buf)
+		loff_t from, size_t len, size_t *retlen, const u_char *buf)
 {
 	struct spi_message	m;
 	const size_t		l = 4 + 64;

drivers/mtd/mtdcore.c

@@ -1889,7 +1889,7 @@ int mtd_read_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len,
 EXPORT_SYMBOL_GPL(mtd_read_user_prot_reg);
 
 int mtd_write_user_prot_reg(struct mtd_info *mtd, loff_t to, size_t len,
-			    size_t *retlen, u_char *buf)
+			    size_t *retlen, const u_char *buf)
 {
 	struct mtd_info *master = mtd_get_master(mtd);
 	int ret;

drivers/mtd/nand/onenand/onenand_base.c

@@ -3167,9 +3167,10 @@ static int onenand_read_user_prot_reg(struct mtd_info *mtd, loff_t from,
  * Write user OTP area.
  */
 static int onenand_write_user_prot_reg(struct mtd_info *mtd, loff_t from,
-			size_t len, size_t *retlen, u_char *buf)
+			size_t len, size_t *retlen, const u_char *buf)
 {
-	return onenand_otp_walk(mtd, from, len, retlen, buf, do_otp_write, MTD_OTP_USER);
+	return onenand_otp_walk(mtd, from, len, retlen, (u_char *)buf,
+				do_otp_write, MTD_OTP_USER);
 }
 
 /**

drivers/mtd/spi-nor/core.h

@@ -211,7 +211,8 @@ struct spi_nor_otp_organization {
  */
 struct spi_nor_otp_ops {
 	int (*read)(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf);
-	int (*write)(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf);
+	int (*write)(struct spi_nor *nor, loff_t addr, size_t len,
+		     const u8 *buf);
 	int (*lock)(struct spi_nor *nor, unsigned int region);
 	int (*is_locked)(struct spi_nor *nor, unsigned int region);
 };
@@ -504,7 +505,8 @@ ssize_t spi_nor_write_data(struct spi_nor *nor, loff_t to, size_t len,
 			   const u8 *buf);
 
 int spi_nor_otp_read_secr(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf);
-int spi_nor_otp_write_secr(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf);
+int spi_nor_otp_write_secr(struct spi_nor *nor, loff_t addr, size_t len,
+			   const u8 *buf);
 int spi_nor_otp_lock_sr2(struct spi_nor *nor, unsigned int region);
 int spi_nor_otp_is_locked_sr2(struct spi_nor *nor, unsigned int region);
 

drivers/mtd/spi-nor/otp.c

@@ -70,7 +70,8 @@ int spi_nor_otp_read_secr(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf)
  *
  * Return: number of bytes written successfully, -errno otherwise
  */
-int spi_nor_otp_write_secr(struct spi_nor *nor, loff_t addr, size_t len, u8 *buf)
+int spi_nor_otp_write_secr(struct spi_nor *nor, loff_t addr, size_t len,
+			   const u8 *buf)
 {
 	enum spi_nor_protocol write_proto;
 	struct spi_mem_dirmap_desc *wdesc;
@@ -241,7 +242,7 @@ out:
 
 static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
 				      size_t total_len, size_t *retlen,
-				      u8 *buf, bool is_write)
+				      const u8 *buf, bool is_write)
 {
 	struct spi_nor *nor = mtd_to_spi_nor(mtd);
 	const struct spi_nor_otp_ops *ops = nor->params->otp.ops;
@@ -285,7 +286,7 @@ static int spi_nor_mtd_otp_read_write(struct mtd_info *mtd, loff_t ofs,
 		if (is_write)
 			ret = ops->write(nor, rstart + rofs, len, buf);
 		else
-			ret = ops->read(nor, rstart + rofs, len, buf);
+			ret = ops->read(nor, rstart + rofs, len, (u8 *)buf);
 		if (ret == 0)
 			ret = -EIO;
 		if (ret < 0)
@@ -310,7 +311,7 @@ static int spi_nor_mtd_otp_read(struct mtd_info *mtd, loff_t from, size_t len,
 }
 
 static int spi_nor_mtd_otp_write(struct mtd_info *mtd, loff_t to, size_t len,
-				 size_t *retlen, u8 *buf)
+				 size_t *retlen, const u8 *buf)
 {
 	return spi_nor_mtd_otp_read_write(mtd, to, len, retlen, buf, true);
 }

include/linux/mtd/mtd.h

@@ -334,7 +334,8 @@ struct mtd_info {
 	int (*_read_user_prot_reg) (struct mtd_info *mtd, loff_t from,
 				    size_t len, size_t *retlen, u_char *buf);
 	int (*_write_user_prot_reg) (struct mtd_info *mtd, loff_t to,
-				     size_t len, size_t *retlen, u_char *buf);
+				     size_t len, size_t *retlen,
+				     const 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,
@@ -518,7 +519,7 @@ int mtd_get_user_prot_info(struct mtd_info *mtd, size_t len, size_t *retlen,
 int mtd_read_user_prot_reg(struct mtd_info *mtd, loff_t from, size_t len,
 			   size_t *retlen, u_char *buf);
 int mtd_write_user_prot_reg(struct mtd_info *mtd, loff_t to, size_t len,
-			    size_t *retlen, u_char *buf);
+			    size_t *retlen, const 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);