diff options
author | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2008-04-19 17:44:31 (GMT) |
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committer | Artem Bityutskiy <Artem.Bityutskiy@nokia.com> | 2008-04-19 17:49:41 (GMT) |
commit | 4bc1dca4b0eb4dfbf100895bfc1256f21e3c901a (patch) | |
tree | 4ccfc207a0b55cfad4247f49bd1bce03d5034560 /drivers/mtd/ubi | |
parent | cbd8a9d2cd6f576ca41022599341bbd8be1b0b27 (diff) | |
download | linux-fsl-qoriq-4bc1dca4b0eb4dfbf100895bfc1256f21e3c901a.tar.xz |
UBI: fix mean EC calculation
(a + b) / (c + d) != a / c + b / d. The old code errornously
assumed this incorrect formuld. Instead, just sum all erase
counters in a 64-bit variable and divide to the number of EBs
at the end.
Thanks to Adrian Hunter for pointing this out.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Diffstat (limited to 'drivers/mtd/ubi')
-rw-r--r-- | drivers/mtd/ubi/scan.c | 41 | ||||
-rw-r--r-- | drivers/mtd/ubi/scan.h | 2 |
2 files changed, 9 insertions, 34 deletions
diff --git a/drivers/mtd/ubi/scan.c b/drivers/mtd/ubi/scan.c index 05aa3e7..96d410e 100644 --- a/drivers/mtd/ubi/scan.c +++ b/drivers/mtd/ubi/scan.c @@ -42,6 +42,7 @@ #include <linux/err.h> #include <linux/crc32.h> +#include <asm/div64.h> #include "ubi.h" #ifdef CONFIG_MTD_UBI_DEBUG_PARANOID @@ -92,27 +93,6 @@ static int add_to_list(struct ubi_scan_info *si, int pnum, int ec, } /** - * commit_to_mean_value - commit intermediate results to the final mean erase - * counter value. - * @si: scanning information - * - * This is a helper function which calculates partial mean erase counter mean - * value and adds it to the resulting mean value. As we can work only in - * integer arithmetic and we want to calculate the mean value of erase counter - * accurately, we first sum erase counter values in @si->ec_sum variable and - * count these components in @si->ec_count. If this temporary @si->ec_sum is - * going to overflow, we calculate the partial mean value - * (@si->ec_sum/@si->ec_count) and add it to @si->mean_ec. - */ -static void commit_to_mean_value(struct ubi_scan_info *si) -{ - si->ec_sum /= si->ec_count; - if (si->ec_sum % si->ec_count >= si->ec_count / 2) - si->mean_ec += 1; - si->mean_ec += si->ec_sum; -} - -/** * validate_vid_hdr - check that volume identifier header is correct and * consistent. * @vid_hdr: the volume identifier header to check @@ -901,15 +881,8 @@ static int process_eb(struct ubi_device *ubi, struct ubi_scan_info *si, int pnum adjust_mean_ec: if (!ec_corr) { - if (si->ec_sum + ec < ec) { - commit_to_mean_value(si); - si->ec_sum = 0; - si->ec_count = 0; - } else { - si->ec_sum += ec; - si->ec_count += 1; - } - + si->ec_sum += ec; + si->ec_count += 1; if (ec > si->max_ec) si->max_ec = ec; if (ec < si->min_ec) @@ -965,9 +938,11 @@ struct ubi_scan_info *ubi_scan(struct ubi_device *ubi) dbg_msg("scanning is finished"); - /* Finish mean erase counter calculations */ - if (si->ec_count) - commit_to_mean_value(si); + /* Calculate mean erase counter */ + if (si->ec_count) { + do_div(si->ec_sum, si->ec_count); + si->mean_ec = si->ec_sum; + } if (si->is_empty) ubi_msg("empty MTD device detected"); diff --git a/drivers/mtd/ubi/scan.h b/drivers/mtd/ubi/scan.h index 46d444a..966b9b6 100644 --- a/drivers/mtd/ubi/scan.h +++ b/drivers/mtd/ubi/scan.h @@ -124,7 +124,7 @@ struct ubi_scan_info { int max_ec; unsigned long long max_sqnum; int mean_ec; - int ec_sum; + uint64_t ec_sum; int ec_count; }; |