[PATCH v3 4/5] mtd: nand: make 'erased check' optional

[Boris Brezillon]

Some ECC controllers do not need the extra 'erased check' done by the core.
Make it optional by creating a new NAND_ECC_DISABLE_ERASED_CHECK flag.

Reed-Solomon ECC engines are guaranteed to generate ff ECC bytes when the
page in empty and are thus able to fix bitflips in erased pages.

The software BCH implementation is also generating ff ECC bytes for empty
pages, and is thus able to fix bitflips in erased pages too.

Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
---
 drivers/mtd/nand/nand_base.c | 20 ++++++++++++++++----
 drivers/mtd/nand/r852.c      |  1 +
 drivers/mtd/nand/tmio_nand.c |  1 +
 drivers/mtd/nand/txx9ndfmc.c |  1 +
 include/linux/mtd/nand.h     |  8 ++++++++
 5 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 9a109a5..3be312d 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1419,7 +1419,8 @@ static int nand_read_subpage(struct mtd_info *mtd, struct nand_chip *chip,
 
 		stat = chip->ecc.correct(mtd, p,
 			&chip->buffers->ecccode[i], &chip->buffers->ecccalc[i]);
-		if (stat == -EBADMSG) {
+		if (stat == -EBADMSG &&
+		    !(chip->ecc.options & NAND_ECC_DISABLE_ERASED_CHECK)) {
 			/* check for empty pages with bitflips */
 			stat = nand_check_erased_ecc_chunk(p, chip->ecc.size,
 						&chip->buffers->ecccode[i],
@@ -1477,7 +1478,8 @@ static int nand_read_page_hwecc(struct mtd_info *mtd, struct nand_chip *chip,
 		int stat;
 
 		stat = chip->ecc.correct(mtd, p, &ecc_code[i], &ecc_calc[i]);
-		if (stat == -EBADMSG) {
+		if (stat == -EBADMSG &&
+		    !(chip->ecc.options & NAND_ECC_DISABLE_ERASED_CHECK)) {
 			/* check for empty pages with bitflips */
 			stat = nand_check_erased_ecc_chunk(p, eccsize,
 						&ecc_code[i], eccbytes,
@@ -1537,7 +1539,8 @@ static int nand_read_page_hwecc_oob_first(struct mtd_info *mtd,
 		chip->ecc.calculate(mtd, p, &ecc_calc[i]);
 
 		stat = chip->ecc.correct(mtd, p, &ecc_code[i], NULL);
-		if (stat == -EBADMSG) {
+		if (stat == -EBADMSG &&
+		    !(chip->ecc.options & NAND_ECC_DISABLE_ERASED_CHECK)) {
 			/* check for empty pages with bitflips */
 			stat = nand_check_erased_ecc_chunk(p, eccsize,
 						&ecc_code[i], eccbytes,
@@ -1600,7 +1603,8 @@ static int nand_read_page_syndrome(struct mtd_info *mtd, struct nand_chip *chip,
 			oob += chip->ecc.postpad;
 		}
 
-		if (stat == -EBADMSG) {
+		if (stat == -EBADMSG &&
+		    !(chip->ecc.options & NAND_ECC_DISABLE_ERASED_CHECK)) {
 			/* check for empty pages with bitflips */
 			stat = nand_check_erased_ecc_chunk(p, chip->ecc.size,
 							   oob - eccstepsize,
@@ -4300,6 +4304,14 @@ int nand_scan_tail(struct mtd_info *mtd)
 		ecc->write_oob_raw = ecc->write_oob;
 
 	/*
+	 * The software implementation does not need the the erased check
+	 * since they already generate ff pattern for an erased page.
+	 */
+	if (ecc->correct == nand_bch_correct_data ||
+	    ecc->correct == nand_correct_data)
+		ecc->options |= NAND_ECC_DISABLE_ERASED_CHECK;
+
+	/*
 	 * The number of bytes available for a client to place data into
 	 * the out of band area.
 	 */
diff --git a/drivers/mtd/nand/r852.c b/drivers/mtd/nand/r852.c
index c9ad7a0..b82e4d9 100644
--- a/drivers/mtd/nand/r852.c
+++ b/drivers/mtd/nand/r852.c
@@ -876,6 +876,7 @@ static int  r852_probe(struct pci_dev *pci_dev, const struct pci_device_id *id)
 	chip->ecc.hwctl = r852_ecc_hwctl;
 	chip->ecc.calculate = r852_ecc_calculate;
 	chip->ecc.correct = r852_ecc_correct;
+	chip->ecc.options |= NAND_ECC_DISABLE_ERASED_CHECK;
 
 	/* TODO: hack */
 	chip->ecc.read_oob = r852_read_oob;
diff --git a/drivers/mtd/nand/tmio_nand.c b/drivers/mtd/nand/tmio_nand.c
index fb8fd35..24192ac 100644
--- a/drivers/mtd/nand/tmio_nand.c
+++ b/drivers/mtd/nand/tmio_nand.c
@@ -415,6 +415,7 @@ static int tmio_probe(struct platform_device *dev)
 	nand_chip->ecc.hwctl = tmio_nand_enable_hwecc;
 	nand_chip->ecc.calculate = tmio_nand_calculate_ecc;
 	nand_chip->ecc.correct = tmio_nand_correct_data;
+	nand_chip->ecc.options |= NAND_ECC_DISABLE_ERASED_CHECK;
 
 	if (data)
 		nand_chip->badblock_pattern = data->badblock_pattern;
diff --git a/drivers/mtd/nand/txx9ndfmc.c b/drivers/mtd/nand/txx9ndfmc.c
index 9c0bc45..d5ca045 100644
--- a/drivers/mtd/nand/txx9ndfmc.c
+++ b/drivers/mtd/nand/txx9ndfmc.c
@@ -336,6 +336,7 @@ static int __init txx9ndfmc_probe(struct platform_device *dev)
 		chip->ecc.correct = txx9ndfmc_correct_data;
 		chip->ecc.hwctl = txx9ndfmc_enable_hwecc;
 		chip->ecc.mode = NAND_ECC_HW;
+		chip->ecc.options |= NAND_ECC_DISABLE_ERASED_CHECK;
 		/* txx9ndfmc_nand_scan will overwrite ecc.size and ecc.bytes */
 		chip->ecc.size = 256;
 		chip->ecc.bytes = 3;
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 19d43b1..88956ab 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -128,6 +128,13 @@ typedef enum {
 #define NAND_ECC_WRITE		1
 /* Enable Hardware ECC before syndrome is read back from flash */
 #define NAND_ECC_READSYN	2
+/*
+ * Disable NAND 'page erased' check. In any case, this check is only done when
+ * ecc.correct() returns -EBADMSG.
+ * Set this flag if your implementation is able to fix bitflips in erased
+ * pages.
+ */
+#define NAND_ECC_DISABLE_ERASED_CHECK	BIT(1)
 
 /* Bit mask for flags passed to do_nand_read_ecc */
 #define NAND_GET_DEVICE		0x80
@@ -500,6 +507,7 @@ struct nand_ecc_ctrl {
 	int strength;
 	int prepad;
 	int postpad;
+	unsigned int options;
 	struct nand_ecclayout	*layout;
 	void *priv;
 	void (*hwctl)(struct mtd_info *mtd, int mode);
-- 
1.9.1