mtd: nand: add nand_check_erased helper functions
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Fri Nov 6 10:59:02 PST 2015
Gitweb: http://git.infradead.org/?p=mtd-2.6.git;a=commit;h=730a43fbc135e593cc3de3b1b895e49c05c8e2dc
Commit: 730a43fbc135e593cc3de3b1b895e49c05c8e2dc
Parent: db66e32e0d2ae1f5070faa589aa460b75780ab47
Author: Boris BREZILLON <boris.brezillon at free-electrons.com>
AuthorDate: Thu Sep 3 18:03:38 2015 +0200
Committer: Brian Norris <computersforpeace at gmail.com>
CommitDate: Mon Sep 21 15:35:04 2015 -0700
mtd: nand: add nand_check_erased helper functions
Add two helper functions to help NAND controller drivers test whether a
specific NAND region is erased or not.
Signed-off-by: Boris Brezillon <boris.brezillon at free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace at gmail.com>
---
drivers/mtd/nand/nand_base.c | 128 +++++++++++++++++++++++++++++++++++++++++++
include/linux/mtd/nand.h | 5 ++
2 files changed, 133 insertions(+)
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index 51f7816..37c0d9d 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -1101,6 +1101,134 @@ 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/include/linux/mtd/nand.h b/include/linux/mtd/nand.h
index 3140b3d..c4d8e30 100644
--- a/include/linux/mtd/nand.h
+++ b/include/linux/mtd/nand.h
@@ -1030,4 +1030,9 @@ struct nand_sdr_timings {
/* get timing characteristics from ONFI timing mode. */
const struct nand_sdr_timings *onfi_async_timing_mode_to_sdr_timings(int mode);
+
+int nand_check_erased_ecc_chunk(void *data, int datalen,
+ void *ecc, int ecclen,
+ void *extraoob, int extraooblen,
+ int threshold);
#endif /* __LINUX_MTD_NAND_H */
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