[PATCH -next v3 2/2] mtd: nand: toshiba: Add support for Toshiba Memory BENAND (Built-in ECC NAND)

[KOBAYASHI Yoshitake]

This patch enables support for Toshiba Memory BENAND. This checks
internal ECC status in read operation when using BENAND and selecting
ECC mode as on-die.

Signed-off-by: KOBAYASHI Yoshitake <yoshitake.kobayashi@xxxxxxxxxxxxx>
---
 drivers/mtd/nand/nand_toshiba.c | 89 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/drivers/mtd/nand/nand_toshiba.c b/drivers/mtd/nand/nand_toshiba.c
index c2c141b..35c0ddf 100644
--- a/drivers/mtd/nand/nand_toshiba.c
+++ b/drivers/mtd/nand/nand_toshiba.c
@@ -17,6 +17,91 @@
 
 #include <linux/mtd/rawnand.h>
 
+/* ECC Status Read Command for BENAND */
+#define TOSHIBA_NAND_CMD_ECC_STATUS	0x7A
+
+/* Recommended to rewrite for BENAND */
+#define TOSHIBA_NAND_STATUS_REWRITE_RECOMMENDED	BIT(3)
+
+static int toshiba_nand_benand_status_chk(struct mtd_info *mtd,
+					  struct nand_chip *chip)
+{
+	unsigned int max_bitflips = 0;
+	u8 status;
+
+	/* Check Read Status */
+	chip->cmdfunc(mtd, NAND_CMD_STATUS, -1, -1);
+	status = chip->read_byte(mtd);
+
+	/*
+	 * TOSHIBA_NAND_CMD_ECC_STATUS is vendor specific command.
+	 * Currently we have no way to send arbitrary sequences of
+	 * CMD+ADDR+DATA cycles and thus cannot support this custom
+	 * TOSHIBA_NAND_CMD_ECC_STATUS operation.
+	 * For now, we set max_bitflips mtd->bitflip_threshold.
+	 */
+	if (status & NAND_STATUS_FAIL) {
+		/* uncorrectable */
+		mtd->ecc_stats.failed++;
+	} else if (status & TOSHIBA_NAND_STATUS_REWRITE_RECOMMENDED) {
+		/* correctable */
+		max_bitflips = mtd->bitflip_threshold;
+		mtd->ecc_stats.corrected += max_bitflips;
+	}
+
+	return max_bitflips;
+}
+
+static int
+toshiba_nand_read_page_benand(struct mtd_info *mtd,
+			      struct nand_chip *chip, uint8_t *buf,
+			      int oob_required, int page)
+{
+	nand_read_page_raw(mtd, chip, buf, oob_required, page);
+
+	return toshiba_nand_benand_status_chk(mtd, chip);
+}
+
+static int
+toshiba_nand_read_subpage_benand(struct mtd_info *mtd,
+				 struct nand_chip *chip, uint32_t data_offs,
+				 uint32_t readlen, uint8_t *bufpoi, int page)
+{
+	uint8_t *p;
+
+	if (data_offs != 0)
+		chip->cmdfunc(mtd, NAND_CMD_RNDOUT, data_offs, -1);
+
+	p = bufpoi + data_offs;
+	chip->read_buf(mtd, p, readlen);
+
+	return toshiba_nand_benand_status_chk(mtd, chip);
+}
+
+static void toshiba_nand_benand_init(struct nand_chip *chip)
+{
+	struct mtd_info *mtd = nand_to_mtd(chip);
+
+	/*
+	 * On BENAND, the entire OOB region can be used by the MTD user.
+	 * The calculated ECC bytes are stored into other isolated
+	 * area which is not accessible to users.
+	 * This is why chip->ecc.bytes = 0.
+	 */
+	chip->ecc.bytes = 0;
+	chip->ecc.size = 512;
+	chip->ecc.strength = 8;
+	chip->ecc.read_page = toshiba_nand_read_page_benand;
+	chip->ecc.read_subpage = toshiba_nand_read_subpage_benand;
+	chip->ecc.write_page = nand_write_page_raw;
+	chip->ecc.read_page_raw = nand_read_page_raw;
+	chip->ecc.write_page_raw = nand_write_page_raw;
+
+	chip->options |= NAND_SUBPAGE_READ;
+
+	mtd_set_ooblayout(mtd, &nand_ooblayout_lp_ops);
+}
+
 static void toshiba_nand_decode_id(struct nand_chip *chip)
 {
 	struct mtd_info *mtd = nand_to_mtd(chip);
@@ -70,6 +155,10 @@ static int toshiba_nand_init(struct nand_chip *chip)
 	if (nand_is_slc(chip))
 		chip->bbt_options |= NAND_BBT_SCAN2NDPAGE;
 
+	if (nand_is_slc(chip) && (chip->id.data[4] & 0x80) /* BENAND */ &&
+	    (chip->ecc.mode == NAND_ECC_ON_DIE))
+		toshiba_nand_benand_init(chip);
+
 	return 0;
 }
 
-- 
2.7.4