From 4bc1dca4b0eb4dfbf100895bfc1256f21e3c901a Mon Sep 17 00:00:00 2001 From: Artem Bityutskiy Date: Sat, 19 Apr 2008 20:44:31 +0300 Subject: 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 --- drivers/mtd/ubi/scan.c | 41 ++++++++--------------------------------- drivers/mtd/ubi/scan.h | 2 +- 2 files changed, 9 insertions(+), 34 deletions(-) (limited to 'drivers/mtd/ubi') diff --git a/drivers/mtd/ubi/scan.c b/drivers/mtd/ubi/scan.c index 05aa3e7daba1..96d410e106ab 100644 --- a/drivers/mtd/ubi/scan.c +++ b/drivers/mtd/ubi/scan.c @@ -42,6 +42,7 @@ #include #include +#include #include "ubi.h" #ifdef CONFIG_MTD_UBI_DEBUG_PARANOID @@ -91,27 +92,6 @@ static int add_to_list(struct ubi_scan_info *si, int pnum, int ec, return 0; } -/** - * 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. @@ -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 46d444af471a..966b9b682a42 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; }; -- cgit v1.2.3-59-g8ed1b