[PATCH v5 5/6] mtd: rawnand: micron: support 8/512 on-die ECC

From: Chris Packham
Date: Thu Jun 21 2018 - 21:29:00 EST

Micron MT29F1G08ABAFAWP-ITE:F supports an on-die ECC with 8 bits
per 512 bytes. Add support for this combination.

Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
---

Notes:
Changes in v2:
- New
Changes in v3:
- Handle reporting of corrected errors that don't require a rewrite, expand
comment for the ECC status bits.
Changes in v4:
- Use a switch statement for handling ECC status
- Update ecc_stats.corrected
Changes in v5:
- Move status checking to different routines for 4/512 and 8/512 assume
the highest number of bit flips for a given status value.

drivers/mtd/nand/raw/nand_micron.c | 100 +++++++++++++++++++++++------
1 file changed, 79 insertions(+), 21 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_micron.c b/drivers/mtd/nand/raw/nand_micron.c
index d30bd4df9b12..f83053562925 100644
--- a/drivers/mtd/nand/raw/nand_micron.c
+++ b/drivers/mtd/nand/raw/nand_micron.c
@@ -18,10 +18,30 @@
#include <linux/mtd/rawnand.h>

/*
- * Special Micron status bit that indicates when the block has been
- * corrected by on-die ECC and should be rewritten
+ * Special Micron status bit 3 indicates that the block has been
+ * corrected by on-die ECC and should be rewritten.
*/
-#define NAND_STATUS_WRITE_RECOMMENDED BIT(3)
+#define NAND_ECC_STATUS_WRITE_RECOMMENDED BIT(3)
+
+/*
+ * On chips with 8-bit ECC and additional bit can be used to distinguish
+ * cases where a errors were corrected without needing a rewrite
+ *
+ * Bit 4 Bit 3 Bit 0 Description
+ * ----- ----- ----- -----------
+ * 0 0 0 No Errors
+ * 0 0 1 Multiple uncorrected errors
+ * 0 1 0 4 - 6 errors corrected, recommend rewrite
+ * 0 1 1 Reserved
+ * 1 0 0 1 - 3 errors corrected
+ * 1 0 1 Reserved
+ * 1 1 0 7 - 8 errors corrected, recommend rewrite
+ */
+#define NAND_ECC_STATUS_MASK (BIT(4) | BIT(3) | BIT(0))
+#define NAND_ECC_STATUS_UNCORRECTABLE BIT(0)
+#define NAND_ECC_STATUS_4_6_CORRECTED BIT(3)
+#define NAND_ECC_STATUS_1_3_CORRECTED BIT(4)
+#define NAND_ECC_STATUS_7_8_CORRECTED (BIT(4) | BIT(3))

struct nand_onfi_vendor_micron {
u8 two_plane_read;
@@ -113,6 +133,54 @@ static int micron_nand_on_die_ecc_setup(struct nand_chip *chip, bool enable)
return nand_set_features(chip, ONFI_FEATURE_ON_DIE_ECC, feature);
}

+
+static int micron_nand_on_die_ecc_status_4(struct mtd_info *mtd,
+ struct nand_chip *chip, u8 status)
+{
+ /*
+ * The internal ECC doesn't tell us the number of bitflips
+ * that have been corrected, but tells us if it recommends to
+ * rewrite the block. If it's the case, then we pretend we had
+ * a number of bitflips equal to the ECC strength, which will
+ * hint the NAND core to rewrite the block.
+ */
+ if (status & NAND_STATUS_FAIL) {
+ mtd->ecc_stats.failed++;
+ } else if (status & NAND_ECC_STATUS_WRITE_RECOMMENDED) {
+ mtd->ecc_stats.corrected += chip->ecc.strength;
+ return chip->ecc.strength;
+ }
+
+ return 0;
+}
+
+static int micron_nand_on_die_ecc_status_8(struct mtd_info *mtd,
+ struct nand_chip *chip, u8 status)
+{
+ /*
+ * With 8/512 we have more information but still don't know precisely
+ * how many bit-flips were seen.
+ */
+ switch (status & NAND_ECC_STATUS_MASK) {
+ case NAND_ECC_STATUS_UNCORRECTABLE:
+ mtd->ecc_stats.failed++;
+ return 0;
+ case NAND_ECC_STATUS_1_3_CORRECTED:
+ mtd->ecc_stats.corrected += 3;
+ return 3;
+ case NAND_ECC_STATUS_4_6_CORRECTED:
+ mtd->ecc_stats.corrected += 6;
+ /* rewrite recommended */
+ return 6;
+ case NAND_ECC_STATUS_7_8_CORRECTED:
+ mtd->ecc_stats.corrected += 8;
+ /* rewrite recommended */
+ return 8;
+ default:
+ return 0;
+ }
+}
+
static int
micron_nand_read_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
uint8_t *buf, int oob_required,
@@ -137,19 +205,10 @@ micron_nand_read_page_on_die_ecc(struct mtd_info *mtd, struct nand_chip *chip,
if (ret)
goto out;

- if (status & NAND_STATUS_FAIL) {
- mtd->ecc_stats.failed++;
- } else if (status & NAND_STATUS_WRITE_RECOMMENDED) {
- /*
- * The internal ECC doesn't tell us the number of bitflips
- * that have been corrected, but tells us if it recommends to
- * rewrite the block. If it's the case, then we pretend we had
- * a number of bitflips equal to the ECC strength, which will
- * hint the NAND core to rewrite the block.
- */
- mtd->ecc_stats.corrected += chip->ecc.strength;
- max_bitflips = chip->ecc.strength;
- }
+ if (chip->ecc.strength == 4)
+ max_bitflips = micron_nand_on_die_ecc_status_4(mtd, chip, status);
+ else
+ max_bitflips = micron_nand_on_die_ecc_status_8(mtd, chip, status);

ret = nand_read_data_op(chip, buf, mtd->writesize, false);
if (!ret && oob_required)
@@ -240,10 +299,9 @@ static int micron_supports_on_die_ecc(struct nand_chip *chip)
return MICRON_ON_DIE_MANDATORY;

/*
- * Some Micron NANDs have an on-die ECC of 4/512, some other
- * 8/512. We only support the former.
+ * We only support on-die ECC of 4/512 or 8/512
*/
- if (chip->ecc_strength_ds != 4)
+ if (chip->ecc_strength_ds != 4 && chip->ecc_strength_ds != 8)
return MICRON_ON_DIE_UNSUPPORTED;

return MICRON_ON_DIE_SUPPORTED;
@@ -275,9 +333,9 @@ static int micron_nand_init(struct nand_chip *chip)
return -EINVAL;
}

- chip->ecc.bytes = 8;
+ chip->ecc.bytes = chip->ecc_strength_ds * 2;
chip->ecc.size = 512;
- chip->ecc.strength = 4;
+ chip->ecc.strength = chip->ecc_strength_ds;
chip->ecc.algo = NAND_ECC_BCH;
chip->ecc.read_page = micron_nand_read_page_on_die_ecc;
chip->ecc.write_page = micron_nand_write_page_on_die_ecc;
--
2.17.1