[PATCH v4 2/2] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter

[Jane Wan]

Per ONFI specification (Rev. 4.0), if all parameter pages have invalid
CRC values, the bit-wise majority may be used to recover the contents of
the parameter pages from the parameter page copies present.

Signed-off-by: Jane Wan <jane....@nokia.com>
---
 drivers/mtd/nand/raw/nand_base.c |   49 ++++++++++++++++++++++++++++++++++----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 72f3a89..dfc341c 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -5086,6 +5086,38 @@ static int nand_flash_detect_ext_param_page(struct 
nand_chip *chip,
        return ret;
 }
 
+#define GET_BIT(bit, val)   (((val) >> (bit)) & 0x01)
+
+/*
+ * Recover NAND parameter page with bit-wise majority
+ */
+static int onfi_recover_param(struct nand_onfi_params *p, int pages)
+{
+       int i, j, k;
+       u8 v, m;
+       u8 *buf;
+
+       buf = (u8 *)p;
+       for (i = 0; i < sizeof(*p); i++) {
+               v = 0;
+               for (j = 0; j < 8; j++) {
+                       m = 0;
+                       for (k = 0; k < pages; k++)
+                               m += GET_BIT(j, buf[k*sizeof(*p) + i]);
+                       if (m > pages/2)
+                               v |= BIT(j);
+               }
+               ((u8 *)p)[i] = v;
+       }
+
+       if (onfi_crc16(ONFI_CRC_BASE, (u8 *)p, 254) ==
+                       le16_to_cpu(p->crc)) {
+               return 1;
+       }
+
+       return 0;
+}
+
 /*
  * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 otherwise.
  */
@@ -5102,7 +5134,7 @@ static int nand_flash_detect_onfi(struct nand_chip *chip)
                return 0;
 
        /* ONFI chip: allocate a buffer to hold its parameter page */
-       p = kzalloc(sizeof(*p), GFP_KERNEL);
+       p = kzalloc((sizeof(*p) * 3), GFP_KERNEL);
        if (!p)
                return -ENOMEM;
 
@@ -5113,21 +5145,28 @@ static int nand_flash_detect_onfi(struct nand_chip 
*chip)
        }
 
        for (i = 0; i < 3; i++) {
-               ret = nand_read_data_op(chip, p, sizeof(*p), true);
+               ret = nand_read_data_op(chip, &p[i], sizeof(*p), true);
                if (ret) {
                        ret = 0;
                        goto free_onfi_param_page;
                }
 
-               if (onfi_crc16(ONFI_CRC_BASE, (uint8_t *)p, 254) ==
+               if (onfi_crc16(ONFI_CRC_BASE, (u8 *)&p[i], 254) ==
                                le16_to_cpu(p->crc)) {
+                       if (i)
+                               memcpy(p, &p[i], sizeof(*p));
                        break;
                }
        }
 
        if (i == 3) {
-               pr_err("Could not find valid ONFI parameter page; aborting\n");
-               goto free_onfi_param_page;
+               pr_err("Could not find valid ONFI parameter page\n");
+               pr_info("Recover ONFI params with bit-wise majority\n");
+               ret = onfi_recover_param(p, 3);
+               if (ret == 0) {
+                       pr_err("ONFI parameter recovery failed, aborting\n");
+                       goto free_onfi_param_page;
+               }
        }
 
        /* Check version */
-- 
1.7.9.5