mtd: rawnand: use bit-wise majority to recover the ONFI param page

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 page from the parameter page copies present.
Signed-off-by: Jane Wan <Jane.Wan@nokia.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/nand/raw/nand_base.c

@@ -5086,6 +5086,37 @@ static int nand_flash_detect_ext_param_page(struct nand_chip *chip,
 	return ret;
 }
 
+/*
+ * 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 val = 0;
+
+		for (j = 0; j < 8; j++) {
+			unsigned int 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.
  */
@@ -5102,7 +5133,7 @@ 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;
 
@@ -5113,22 +5144,33 @@ 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");
+		const void *srcbufs[3] = {p, p + 1, p + 2};
+
+		pr_warn("Could not find a valid ONFI parameter page, trying bit-wise majority to recover it\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 */
 	val = le16_to_cpu(p->revision);