mtd: rawnand: sunxi: do not count BBM bytes twice

BBM is already part of USER_DATA section, so we should not remove it twice

This was working ok because we are on the safe size, advertising that
there was 2 bytes less available than in reality.

But we can't change old platforms, since it may lead to a different ECC
strength, so, introduce a legacy flag for old platforms, and switch the
new platforms to the correct count.

Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

Author: richard-bootlin

drivers/mtd/nand/raw/sunxi_nand.c

@@ -275,6 +275,8 @@ static inline struct sunxi_nand_chip *to_sunxi_nand(struct nand_chip *nand)
  * @has_ecc_block_512:	If the ECC can handle 512B or only 1024B chuncks
  * @has_ecc_clk:	If the controller needs an ECC clock.
  * @has_mbus_clk:	If the controller needs a mbus clock.
+ * @legacy_max_strength:If the maximize strength function was off by 2 bytes
+ *			NB: this should not be used in new controllers
  * @reg_io_data:	I/O data register
  * @reg_ecc_err_cnt:	ECC error counter register
  * @reg_user_data:	User data register
@@ -304,6 +306,7 @@ struct sunxi_nfc_caps {
 	bool has_ecc_block_512;
 	bool has_ecc_clk;
 	bool has_mbus_clk;
+	bool legacy_max_strength;
 	unsigned int reg_io_data;
 	unsigned int reg_ecc_err_cnt;
 	unsigned int reg_user_data;
@@ -1805,10 +1808,22 @@ static int sunxi_nand_hw_ecc_ctrl_init(struct nand_chip *nand,
 		ecc->size = 1024;
 		nsectors = mtd->writesize / ecc->size;
 
-		/* Reserve 2 bytes for the BBM */
-		bytes = (mtd->oobsize - 2) / nsectors;
+		/*
+		 * The 2 BBM bytes should not be removed from the grand total,
+		 * because they are part of the USER_DATA_SZ.
+		 * But we can't modify that for older platform since it may
+		 * result in a stronger ECC at the end, and break the
+		 * compatibility.
+		 */
+		if (nfc->caps->legacy_max_strength)
+			bytes = (mtd->oobsize - 2) / nsectors;
+		else
+			bytes = mtd->oobsize / nsectors;
 
-		/* 4 non-ECC bytes are added before each ECC bytes section */
+		/*
+		 * USER_DATA_SZ non-ECC bytes are added before each ECC bytes
+		 * section, they contain the 2 BBM bytes
+		 */
 		bytes -= USER_DATA_SZ;
 
 		/* and bytes has to be even. */
@@ -2373,6 +2388,7 @@ static const u8 sunxi_user_data_len_h6[] = {
 
 static const struct sunxi_nfc_caps sunxi_nfc_a10_caps = {
 	.has_ecc_block_512 = true,
+	.legacy_max_strength = true,
 	.reg_io_data = NFC_REG_A10_IO_DATA,
 	.reg_ecc_err_cnt = NFC_REG_A10_ECC_ERR_CNT,
 	.reg_user_data = NFC_REG_A10_USER_DATA,
@@ -2394,6 +2410,7 @@ static const struct sunxi_nfc_caps sunxi_nfc_a10_caps = {
 static const struct sunxi_nfc_caps sunxi_nfc_a23_caps = {
 	.has_mdma = true,
 	.has_ecc_block_512 = true,
+	.legacy_max_strength = true,
 	.reg_io_data = NFC_REG_A23_IO_DATA,
 	.reg_ecc_err_cnt = NFC_REG_A10_ECC_ERR_CNT,
 	.reg_user_data = NFC_REG_A10_USER_DATA,