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authorArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2008-04-19 13:44:31 -0400
committerArtem Bityutskiy <Artem.Bityutskiy@nokia.com>2008-04-19 13:49:41 -0400
commit4bc1dca4b0eb4dfbf100895bfc1256f21e3c901a (patch)
tree4ccfc207a0b55cfad4247f49bd1bce03d5034560 /drivers/mtd/ubi/scan.c
parentcbd8a9d2cd6f576ca41022599341bbd8be1b0b27 (diff)
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/scan.c')
-rw-r--r--drivers/mtd/ubi/scan.c41
1 files changed, 8 insertions, 33 deletions
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 @@
42 42
43#include <linux/err.h> 43#include <linux/err.h>
44#include <linux/crc32.h> 44#include <linux/crc32.h>
45#include <asm/div64.h>
45#include "ubi.h" 46#include "ubi.h"
46 47
47#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID 48#ifdef CONFIG_MTD_UBI_DEBUG_PARANOID
@@ -92,27 +93,6 @@ static int add_to_list(struct ubi_scan_info *si, int pnum, int ec,
92} 93}
93 94
94/** 95/**
95 * commit_to_mean_value - commit intermediate results to the final mean erase
96 * counter value.
97 * @si: scanning information
98 *
99 * This is a helper function which calculates partial mean erase counter mean
100 * value and adds it to the resulting mean value. As we can work only in
101 * integer arithmetic and we want to calculate the mean value of erase counter
102 * accurately, we first sum erase counter values in @si->ec_sum variable and
103 * count these components in @si->ec_count. If this temporary @si->ec_sum is
104 * going to overflow, we calculate the partial mean value
105 * (@si->ec_sum/@si->ec_count) and add it to @si->mean_ec.
106 */
107static void commit_to_mean_value(struct ubi_scan_info *si)
108{
109 si->ec_sum /= si->ec_count;
110 if (si->ec_sum % si->ec_count >= si->ec_count / 2)
111 si->mean_ec += 1;
112 si->mean_ec += si->ec_sum;
113}
114
115/**
116 * validate_vid_hdr - check that volume identifier header is correct and 96 * validate_vid_hdr - check that volume identifier header is correct and
117 * consistent. 97 * consistent.
118 * @vid_hdr: the volume identifier header to check 98 * @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
901 881
902adjust_mean_ec: 882adjust_mean_ec:
903 if (!ec_corr) { 883 if (!ec_corr) {
904 if (si->ec_sum + ec < ec) { 884 si->ec_sum += ec;
905 commit_to_mean_value(si); 885 si->ec_count += 1;
906 si->ec_sum = 0;
907 si->ec_count = 0;
908 } else {
909 si->ec_sum += ec;
910 si->ec_count += 1;
911 }
912
913 if (ec > si->max_ec) 886 if (ec > si->max_ec)
914 si->max_ec = ec; 887 si->max_ec = ec;
915 if (ec < si->min_ec) 888 if (ec < si->min_ec)
@@ -965,9 +938,11 @@ struct ubi_scan_info *ubi_scan(struct ubi_device *ubi)
965 938
966 dbg_msg("scanning is finished"); 939 dbg_msg("scanning is finished");
967 940
968 /* Finish mean erase counter calculations */ 941 /* Calculate mean erase counter */
969 if (si->ec_count) 942 if (si->ec_count) {
970 commit_to_mean_value(si); 943 do_div(si->ec_sum, si->ec_count);
944 si->mean_ec = si->ec_sum;
945 }
971 946
972 if (si->is_empty) 947 if (si->is_empty)
973 ubi_msg("empty MTD device detected"); 948 ubi_msg("empty MTD device detected");