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From:   Jane Wan <Jane.Wan@nokia.com>
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        ties.bos@nokia.com, Jane Wan <Jane.Wan@nokia.com>
Subject: [PATCH v6] mtd: rawnand: use bit-wise majority to recover the contents of ONFI parameter
Date:   Thu, 10 May 2018 14:28:37 -0700
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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>
---
v6: support the cases that srcbufs are not contiguous
v5: make the bit-wise majority functon generic
v4: move the bit-wise majority code in a separate function
v3: fix warning message detected by kbuild test robot
v2: rebase the changes on top of v4.17-rc1

 drivers/mtd/nand/raw/nand_base.c |   52 ++++++++++++++++++++++++++++++++++----
 1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/nand/raw/nand_base.c b/drivers/mtd/nand/raw/nand_base.c
index 72f3a89..acf905c 100644
--- a/drivers/mtd/nand/raw/nand_base.c
+++ b/drivers/mtd/nand/raw/nand_base.c
@@ -5087,6 +5087,35 @@ static int nand_flash_detect_ext_param_page(struct nand_chip *chip,
 }
 
 /*
+ * Recover data with bit-wise majority
+ */
+static void nand_bit_wise_majority(const void **srcbufs,
+				   unsigned int nsrcbufs,
+				   void *dstbuf,
+				   unsigned int bufsize)
+{
+	int i, j, k;
+
+	for (i = 0; i < bufsize; i++) {
+		u8 cnt, val;
+
+		val = 0;
+		for (j = 0; j < 8; j++) {
+			cnt = 0;
+			for (k = 0; k < nsrcbufs; k++) {
+				const u8 *srcbuf = srcbufs[k];
+
+				if (srcbuf[i] & BIT(j))
+					cnt++;
+			}
+			if (cnt > nsrcbufs / 2)
+				val |= BIT(j);
+		}
+		((u8 *)dstbuf)[i] = val;
+	}
+}
+
+/*
  * Check if the NAND chip is ONFI compliant, returns 1 if it is, 0 otherwise.
  */
 static int nand_flash_detect_onfi(struct nand_chip *chip)
@@ -5102,7 +5131,7 @@ 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 +5142,34 @@ 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;
+		const void *srcbufs[3] = {p, p + 1, p + 2};
+
+		pr_err("Could not find valid ONFI parameter page\n");
+		pr_info("Recover ONFI params with bit-wise majority\n");
+
+		nand_bit_wise_majority(srcbufs, ARRAY_SIZE(srcbufs), p,
+				       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