[PATCH v5 2/2] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter

[Jane Wan <Jane.Wan@nokia.com>]

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.Wan@nokia.com>
---
 drivers/mtd/nand/raw/nand_base.c |   46 +++++++++++++++++++++++++++++++++-----
 1 file changed, 41 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 72f3a89..a7c2507 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -5086,6 +5086,34 @@ static int nand_flash_detect_ext_param_page(struct nand_chip *chip,
 	return ret;
 }
 
+#define GET_BIT(bit, val)   (((val) >> (bit)) & 0x01)
+
+/*
+ * Recover data with bit-wise majority
+ */
+static void nand_bit_wise_majority(const void **srcbufs,
+				   void *dstbuf,
+				   unsigned int nbufs,
+				   unsigned int bufsize)
+{
+	int i, j, k;
+	u8 v, m;
+	u8 *p;
+
+	p = *(u8 **)srcbufs;
+	for (i = 0; i < bufsize; i++) {
+		v = 0;
+		for (j = 0; j < 8; j++) {
+			m = 0;
+			for (k = 0; k < nbufs; k++)
+				m += GET_BIT(j, p[k*bufsize + i]);
+			if (m > nbufs/2)
+				v |= BIT(j);
+		}
+		((u8 *)dstbuf)[i] = v;
+	}
+}
+
 /*
  * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 otherwise.
  */
@@ -5102,7 +5130,7 @@ 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 +5141,29 @@ 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");
+		nand_bit_wise_majority((const void **)&p, p, 3, sizeof(*p));
+		if (onfi_crc16(ONFI_CRC_BASE, (u8 *)p, 254) !=
+				le16_to_cpu(p->crc)) {
+			pr_err("ONFI parameter recovery failed, aborting\n");
+			goto free_onfi_param_page;
+		}
 	}
 
 	/* Check version */
-- 
1.7.9.5