[V3, 1/2] mtd: brcmnand: Add check for erased page bitflips

Kamal Dasu
2016-06-09T21:18:31Z

Check for erased page bitflips in a page. And if well within
threshold return data as all 0xff. Apply sw check for controller
version < 7.2. Controller vesion >= 7.2 has hw support.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
---
V3 changes
Return the max bitflips from a sector within a page
V2 changes
Added use of nand_check_erased_ecc_chunk
Restrict change to older controller < 7.2
---

drivers/mtd/nand/brcmnand/brcmnand.c | 62 ++++++++++++++++++++++++++++++++++++
1 file changed, 62 insertions(+)

diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
index b76ad7c..7ee9617 100644
--- a/drivers/mtd/nand/brcmnand/brcmnand.c
+++ b/drivers/mtd/nand/brcmnand/brcmnand.c
@@ -1545,6 +1545,56 @@ static int brcmnand_read_by_pio(struct mtd_info *mtd, struct nand_chip *chip,
return ret;
}

+/*
+ * Check a page to see if it is erased (w/ bitflips) after an uncorrectable ECC
+ * error
+ *
+ * Because the HW ECC signals an ECC error if an erase paged has even a single
+ * bitflip, we must check each ECC error to see if it is actually an erased
+ * page with bitflips, not a truly corrupted page.
+ *
+ * On a real error, return a negative error code (-EBADMSG for ECC error), and
+ * buf will contain raw data.
+ * Otherwise, buf gets filled with 0xffs and return the maximum number of
+ * bitflips-per-ECC-sector to the caller.
+ *
+ */
+static int brcmstb_nand_verify_erased_page(struct mtd_info *mtd,
+ struct nand_chip *chip, void *buf, u64 addr)
+{
+ int i, sas;
+ void *oob = chip->oob_poi;
+ int bitflips = 0;
+ int page = addr >> chip->page_shift;
+ int ret;
+
+ if (!buf) {
+ buf = chip->buffers->databuf;
+ /* Invalidate page cache */
+ chip->pagebuf = -1;
+ }
+
+ sas = mtd->oobsize / chip->ecc.steps;
+
+ /* read without ecc for verification */
+ chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
+ ret = chip->ecc.read_page_raw(mtd, chip, buf, true, page);
+ if (ret)
+ return ret;
+
+ for (i = 0; i < chip->ecc.steps; i++, oob += sas) {
+ ret = nand_check_erased_ecc_chunk(buf, chip->ecc.size,
+ oob, sas, NULL, 0,
+ chip->ecc.strength);
+ if (ret < 0)
+ return ret;
+
+ bitflips = max(bitflips, ret);
+ }
+
+ return bitflips;
+}
+
static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
u64 addr, unsigned int trans, u32 *buf, u8 *oob)
{
@@ -1575,6 +1625,18 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
}

if (mtd_is_eccerr(err)) {
+ /*
+ * Controller version 7.2 has hw encoder to detect erased page
+ * bitflips, apply sw verification for older controllers only
+ */
+ if (ctrl->nand_version < 0x0702) {
+ err = brcmstb_nand_verify_erased_page(mtd, chip, buf,
+ addr);
+ /* erased page bitflips corrected */
+ if (err > 0)
+ return err;
+ }
+
dev_dbg(ctrl->dev, "uncorrectable error at 0x%llx\n",
(unsigned long long)err_addr);
mtd->ecc_stats.failed++;
--
1.9.1