[PATCH v3 1/2] mtd: spi-nand: Add read retry support

[Cheng Ming Lin]

From: Cheng Ming Lin <chengminglin at mxic.com.tw>

When the host ECC fails to correct the data error of NAND device,
there's a special read for data recovery method which can be setup
by the host for the next read. There are several retry levels that
can be attempted until the lost data is recovered or definitely
assumed lost.

Signed-off-by: Cheng Ming Lin <chengminglin at mxic.com.tw>
---
 drivers/mtd/nand/spi/core.c | 35 +++++++++++++++++++++++++++++++++--
 include/linux/mtd/spinand.h | 14 ++++++++++++++
 2 files changed, 47 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/spi/core.c b/drivers/mtd/nand/spi/core.c
index 4d76f9f71a0e..3f72d94c09f3 100644
--- a/drivers/mtd/nand/spi/core.c
+++ b/drivers/mtd/nand/spi/core.c
@@ -671,11 +671,15 @@ static int spinand_mtd_regular_page_read(struct mtd_info *mtd, loff_t from,
 {
 	struct spinand_device *spinand = mtd_to_spinand(mtd);
 	struct nand_device *nand = mtd_to_nanddev(mtd);
+	struct mtd_ecc_stats old_stats;
 	struct nand_io_iter iter;
 	bool disable_ecc = false;
 	bool ecc_failed = false;
+	unsigned int retry_mode = 0;
 	int ret;
 
+	old_stats = mtd->ecc_stats;
+
 	if (ops->mode == MTD_OPS_RAW || !mtd->ooblayout)
 		disable_ecc = true;
 
@@ -687,18 +691,43 @@ static int spinand_mtd_regular_page_read(struct mtd_info *mtd, loff_t from,
 		if (ret)
 			break;
 
+read_retry:
 		ret = spinand_read_page(spinand, &iter.req);
 		if (ret < 0 && ret != -EBADMSG)
 			break;
 
-		if (ret == -EBADMSG)
+		if (ret == -EBADMSG && spinand->set_read_retry) {
+			if (spinand->read_retries && (++retry_mode < spinand->read_retries)) {
+				ret = spinand->set_read_retry(spinand, retry_mode);
+				if (ret < 0) {
+					ecc_failed = true;
+					return ret;
+				}
+
+				/* Reset ecc_stats; retry */
+				mtd->ecc_stats = old_stats;
+				goto read_retry;
+			} else {
+				/* No more retry modes; real failure */
+				ecc_failed = true;
+			}
+		} else if (ret == -EBADMSG) {
 			ecc_failed = true;
-		else
+		} else {
 			*max_bitflips = max_t(unsigned int, *max_bitflips, ret);
+		}
 
 		ret = 0;
 		ops->retlen += iter.req.datalen;
 		ops->oobretlen += iter.req.ooblen;
+
+		/* Reset to retry mode 0 */
+		if (retry_mode) {
+			retry_mode = 0;
+			ret = spinand->set_read_retry(spinand, retry_mode);
+			if (ret < 0)
+				return ret;
+		}
 	}
 
 	if (ecc_failed && !ret)
@@ -1268,6 +1297,8 @@ int spinand_match_and_init(struct spinand_device *spinand,
 		spinand->id.len = 1 + table[i].devid.len;
 		spinand->select_target = table[i].select_target;
 		spinand->set_cont_read = table[i].set_cont_read;
+		spinand->read_retries = table[i].read_retries;
+		spinand->set_read_retry = table[i].set_read_retry;
 
 		op = spinand_select_op_variant(spinand,
 					       info->op_variants.read_cache);
diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
index 702e5fb13dae..bbfef90135f5 100644
--- a/include/linux/mtd/spinand.h
+++ b/include/linux/mtd/spinand.h
@@ -339,6 +339,8 @@ struct spinand_ondie_ecc_conf {
  * @select_target: function used to select a target/die. Required only for
  *		   multi-die chips
  * @set_cont_read: enable/disable continuous cached reads
+ * @read_retries: the number of read retry modes supported
+ * @set_read_retry: enable/disable read retry for data recovery
  *
  * Each SPI NAND manufacturer driver should have a spinand_info table
  * describing all the chips supported by the driver.
@@ -359,6 +361,9 @@ struct spinand_info {
 			     unsigned int target);
 	int (*set_cont_read)(struct spinand_device *spinand,
 			     bool enable);
+	unsigned int read_retries;
+	int (*set_read_retry)(struct spinand_device *spinand,
+			     unsigned int read_retry);
 };
 
 #define SPINAND_ID(__method, ...)					\
@@ -387,6 +392,10 @@ struct spinand_info {
 #define SPINAND_CONT_READ(__set_cont_read)				\
 	.set_cont_read = __set_cont_read,
 
+#define SPINAND_READ_RETRY(__read_retries, __set_read_retry)		\
+	.read_retries = __read_retries,				\
+	.set_read_retry = __set_read_retry,
+
 #define SPINAND_INFO(__model, __id, __memorg, __eccreq, __op_variants,	\
 		     __flags, ...)					\
 	{								\
@@ -436,6 +445,8 @@ struct spinand_dirmap {
  *		A per-transfer check must of course be done to ensure it is
  *		actually relevant to enable this feature.
  * @set_cont_read: Enable/disable the continuous read feature
+ * @read_retries: the number of read retry modes supported
+ * @set_read_retry: Enable/disable the read retry feature
  * @priv: manufacturer private data
  */
 struct spinand_device {
@@ -469,6 +480,9 @@ struct spinand_device {
 	bool cont_read_possible;
 	int (*set_cont_read)(struct spinand_device *spinand,
 			     bool enable);
+	unsigned int read_retries;
+	int (*set_read_retry)(struct spinand_device *spinand,
+			     unsigned int retry_mode);
 };
 
 /**
-- 
2.25.1