mtd: nand: add core support for on-die ECC

[Linux-MTD Mailing List]

Gitweb:     http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=785818fa8385fe55dab253e42a4c6728fca61333
Commit:     785818fa8385fe55dab253e42a4c6728fca61333
Parent:     85f94b5ef0eede10e7071f9e7e5b864ffad96d72
Author:     Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
AuthorDate: Sat Apr 29 11:06:43 2017 +0200
Committer:  Boris Brezillon <boris.brezillon at free-electrons.com>
CommitDate: Mon May 15 13:18:26 2017 +0200

    mtd: nand: add core support for on-die ECC
    
    A number of NAND flashes have a capability called "on-die ECC" where the
    NAND chip itself is capable of detecting and correcting errors.
    
    Linux already has support for using the ECC implementation of the NAND
    controller, or a software based ECC implementation, but not for using
    the ECC implementation of the NAND controller. However, such an
    implementation is sometimes useful in situations where the NAND
    controller provides ECC algorithms that are not strong enough for the
    NAND chip used on the system. A typical case is a NAND chip that
    requires a 4-bit ECC, while the NAND controller only provides a 1-bit
    ECC algorithm.
    
    This commit introduces the support for the NAND_ECC_ON_DIE ECC mode:
    
     - Parsing of the "on-die" value for the "nand-ecc-mode" Device Tree
       property
    
     - Handling NAND_ECC_ON_DIE case in nand_scan_tail(). The idea is that
       the vendor specific code for the NAND chip must implement
       ->read_page() and ->write_page(). It may optionally provide its own
       ->read_page_raw() and ->write_page_raw() as well. For OOB operation,
       we assume the standard operations are good enough, but they can be
       overridden by the vendor specific code if needed.
    
    Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
    Reviewed-by: Richard Weinberger <richard at nod.at>
    Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
---
 drivers/mtd/nand/nand_base.c | 13 +++++++++++++
 include/linux/mtd/nand.h     |  1 +
 2 files changed, 14 insertions(+)

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index d474378..f49aecd 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -4177,6 +4177,7 @@ static const char * const nand_ecc_modes[] = {
 	[NAND_ECC_HW]		= "hw",
 	[NAND_ECC_HW_SYNDROME]	= "hw_syndrome",
 	[NAND_ECC_HW_OOB_FIRST]	= "hw_oob_first",
+	[NAND_ECC_ON_DIE]	= "on-die",
 };
 
 static int of_get_nand_ecc_mode(struct device_node *np)
@@ -4717,6 +4718,18 @@ int nand_scan_tail(struct mtd_info *mtd)
 		}
 		break;
 
+	case NAND_ECC_ON_DIE:
+		if (!ecc->read_page || !ecc->write_page) {
+			WARN(1, "No ECC functions supplied; on-die ECC not possible\n");
+			ret = -EINVAL;
+			goto err_free;
+		}
+		if (!ecc->read_oob)
+			ecc->read_oob = nand_read_oob_std;
+		if (!ecc->write_oob)
+			ecc->write_oob = nand_write_oob_std;
+		break;
+
 	case NAND_ECC_NONE:
 		pr_warn("NAND_ECC_NONE selected by board driver. This is not recommended!\n");
 		ecc->read_page = nand_read_page_raw;
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 8f67b15..6035220 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -116,6 +116,7 @@ typedef enum {
 	NAND_ECC_HW,
 	NAND_ECC_HW_SYNDROME,
 	NAND_ECC_HW_OOB_FIRST,
+	NAND_ECC_ON_DIE,
 } nand_ecc_modes_t;
 
 enum nand_ecc_algo {