Merge branch 'for-next/mtd'

3 files changed, 173 insertions, 2 deletions

diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index ca48f59de1..554d3d2f96 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -907,6 +907,134 @@ out:
 EXPORT_SYMBOL(nand_lock);
 
 /**
+ * nand_check_erased_buf - check if a buffer contains (almost) only 0xff data
+ * @buf: buffer to test
+ * @len: buffer length
+ * @bitflips_threshold: maximum number of bitflips
+ *
+ * Check if a buffer contains only 0xff, which means the underlying region
+ * has been erased and is ready to be programmed.
+ * The bitflips_threshold specify the maximum number of bitflips before
+ * considering the region is not erased.
+ * Note: The logic of this function has been extracted from the memweight
+ * implementation, except that nand_check_erased_buf function exit before
+ * testing the whole buffer if the number of bitflips exceed the
+ * bitflips_threshold value.
+ *
+ * Returns a positive number of bitflips less than or equal to
+ * bitflips_threshold, or -ERROR_CODE for bitflips in excess of the
+ * threshold.
+ */
+static int nand_check_erased_buf(void *buf, int len, int bitflips_threshold)
+{
+	const unsigned char *bitmap = buf;
+	int bitflips = 0;
+	int weight;
+
+	for (; len && ((uintptr_t)bitmap) % sizeof(long);
+	     len--, bitmap++) {
+		weight = hweight8(*bitmap);
+		bitflips += BITS_PER_BYTE - weight;
+		if (unlikely(bitflips > bitflips_threshold))
+			return -EBADMSG;
+	}
+
+	for (; len >= sizeof(long);
+	     len -= sizeof(long), bitmap += sizeof(long)) {
+		weight = hweight_long(*((unsigned long *)bitmap));
+		bitflips += BITS_PER_LONG - weight;
+		if (unlikely(bitflips > bitflips_threshold))
+			return -EBADMSG;
+	}
+
+	for (; len > 0; len--, bitmap++) {
+		weight = hweight8(*bitmap);
+		bitflips += BITS_PER_BYTE - weight;
+		if (unlikely(bitflips > bitflips_threshold))
+			return -EBADMSG;
+	}
+
+	return bitflips;
+}
+
+/**
+ * nand_check_erased_ecc_chunk - check if an ECC chunk contains (almost) only
+ *				 0xff data
+ * @data: data buffer to test
+ * @datalen: data length
+ * @ecc: ECC buffer
+ * @ecclen: ECC length
+ * @extraoob: extra OOB buffer
+ * @extraooblen: extra OOB length
+ * @bitflips_threshold: maximum number of bitflips
+ *
+ * Check if a data buffer and its associated ECC and OOB data contains only
+ * 0xff pattern, which means the underlying region has been erased and is
+ * ready to be programmed.
+ * The bitflips_threshold specify the maximum number of bitflips before
+ * considering the region as not erased.
+ *
+ * Note:
+ * 1/ ECC algorithms are working on pre-defined block sizes which are usually
+ *    different from the NAND page size. When fixing bitflips, ECC engines will
+ *    report the number of errors per chunk, and the NAND core infrastructure
+ *    expect you to return the maximum number of bitflips for the whole page.
+ *    This is why you should always use this function on a single chunk and
+ *    not on the whole page. After checking each chunk you should update your
+ *    max_bitflips value accordingly.
+ * 2/ When checking for bitflips in erased pages you should not only check
+ *    the payload data but also their associated ECC data, because a user might
+ *    have programmed almost all bits to 1 but a few. In this case, we
+ *    shouldn't consider the chunk as erased, and checking ECC bytes prevent
+ *    this case.
+ * 3/ The extraoob argument is optional, and should be used if some of your OOB
+ *    data are protected by the ECC engine.
+ *    It could also be used if you support subpages and want to attach some
+ *    extra OOB data to an ECC chunk.
+ *
+ * Returns a positive number of bitflips less than or equal to
+ * bitflips_threshold, or -ERROR_CODE for bitflips in excess of the
+ * threshold. In case of success, the passed buffers are filled with 0xff.
+ */
+int nand_check_erased_ecc_chunk(void *data, int datalen,
+				void *ecc, int ecclen,
+				void *extraoob, int extraooblen,
+				int bitflips_threshold)
+{
+	int data_bitflips = 0, ecc_bitflips = 0, extraoob_bitflips = 0;
+
+	data_bitflips = nand_check_erased_buf(data, datalen,
+					      bitflips_threshold);
+	if (data_bitflips < 0)
+		return data_bitflips;
+
+	bitflips_threshold -= data_bitflips;
+
+	ecc_bitflips = nand_check_erased_buf(ecc, ecclen, bitflips_threshold);
+	if (ecc_bitflips < 0)
+		return ecc_bitflips;
+
+	bitflips_threshold -= ecc_bitflips;
+
+	extraoob_bitflips = nand_check_erased_buf(extraoob, extraooblen,
+						  bitflips_threshold);
+	if (extraoob_bitflips < 0)
+		return extraoob_bitflips;
+
+	if (data_bitflips)
+		memset(data, 0xff, datalen);
+
+	if (ecc_bitflips)
+		memset(ecc, 0xff, ecclen);
+
+	if (extraoob_bitflips)
+		memset(extraoob, 0xff, extraooblen);
+
+	return data_bitflips + ecc_bitflips + extraoob_bitflips;
+}
+EXPORT_SYMBOL(nand_check_erased_ecc_chunk);
+
+/**
  * nand_read_page_raw - [INTERN] read raw page data without ecc
  * @mtd: mtd info structure
  * @chip: nand chip info structure
diff --git a/drivers/mtd/nand/nand_mxs.c b/drivers/mtd/nand/nand_mxs.c
index b3767e6cbe..7635e2a418 100644
--- a/drivers/mtd/nand/nand_mxs.c
+++ b/drivers/mtd/nand/nand_mxs.c
@@ -737,6 +737,8 @@ static int mxs_nand_ecc_read_page(struct mtd_info *mtd, struct nand_chip *nand,
 	/* Read DMA completed, now do the mark swapping. */
 	mxs_nand_swap_block_mark(mtd, nand_info->data_buf, nand_info->oob_buf);
 
+	memcpy(buf, nand_info->data_buf, mtd->writesize);
+
 	/* Loop over status bytes, accumulating ECC status. */
 	status = nand_info->oob_buf + mxs_nand_aux_status_offset();
 	for (i = 0; i < mxs_nand_ecc_chunk_cnt(mtd->writesize); i++) {
@@ -747,6 +749,44 @@ static int mxs_nand_ecc_read_page(struct mtd_info *mtd, struct nand_chip *nand,
 			continue;
 
 		if (status[i] == 0xfe) {
+			int flips;
+
+			/*
+			 * The ECC hardware has an uncorrectable ECC status
+			 * code in case we have bitflips in an erased page. As
+			 * nothing was written into this subpage the ECC is
+			 * obviously wrong and we can not trust it. We assume
+			 * at this point that we are reading an erased page and
+			 * try to correct the bitflips in buffer up to
+			 * ecc_strength bitflips. If this is a page with random
+			 * data, we exceed this number of bitflips and have a
+			 * ECC failure. Otherwise we use the corrected buffer.
+			 */
+			if (i == 0) {
+				/* The first block includes metadata */
+				flips = nand_check_erased_ecc_chunk(
+						buf + i * MXS_NAND_CHUNK_DATA_CHUNK_SIZE,
+						MXS_NAND_CHUNK_DATA_CHUNK_SIZE,
+						NULL, 0,
+						nand_info->oob_buf,
+						MXS_NAND_METADATA_SIZE,
+						mtd->ecc_strength);
+			} else {
+				flips = nand_check_erased_ecc_chunk(
+						buf + i * MXS_NAND_CHUNK_DATA_CHUNK_SIZE,
+						MXS_NAND_CHUNK_DATA_CHUNK_SIZE,
+						NULL, 0,
+						NULL, 0,
+						mtd->ecc_strength);
+			}
+
+			if (flips > 0) {
+				max_bitflips = max_t(unsigned int,
+						     max_bitflips, flips);
+				corrected += flips;
+				continue;
+			}
+
 			failed++;
 			continue;
 		}
@@ -772,8 +812,6 @@ static int mxs_nand_ecc_read_page(struct mtd_info *mtd, struct nand_chip *nand,
 
 	nand->oob_poi[0] = nand_info->oob_buf[0];
 
-	memcpy(buf, nand_info->data_buf, mtd->writesize);
-
 	ret = 0;
 rtn:
 	mxs_nand_return_dma_descs(nand_info);
diff --git a/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index f126cd9fbf..83d664e7ee 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -46,6 +46,11 @@ extern int nand_lock(struct mtd_info *mtd, loff_t ofs, uint64_t len);
 /* unlocks specified locked blocks */
 extern int nand_unlock(struct mtd_info *mtd, loff_t ofs, uint64_t len);
 
+extern int nand_check_erased_ecc_chunk(void *data, int datalen,
+				       void *ecc, int ecclen,
+				       void *extraoob, int extraooblen,
+				       int bitflips_threshold);
+
 /* The maximum number of NAND chips in an array */
 #define NAND_MAX_CHIPS		8