mtd: brcmnand: Add check for erased page bitflips

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>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
index 0a54a0f..f0b0672 100644 (file)
--- a/drivers/mtd/nand/brcmnand/brcmnand.c
+++ b/drivers/mtd/nand/brcmnand/brcmnand.c
@@ -1602,6 +1602,56 @@ 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)
 {
@@ -1632,6 +1682,18 @@ 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++;