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-rw-r--r--README3
-rw-r--r--common/cmd_mem.c5
-rw-r--r--doc/README.memory-test98
-rw-r--r--doc/feature-removal-schedule.txt17
-rw-r--r--include/config_cmd_all.h3
-rw-r--r--include/config_cmd_default.h3
6 files changed, 125 insertions, 4 deletions
diff --git a/README b/README
index 42544ce..869694f 100644
--- a/README
+++ b/README
@@ -860,7 +860,8 @@ The following options need to be configured:
(requires CONFIG_CMD_MEMORY and CONFIG_MD5)
CONFIG_CMD_MEMINFO * Display detailed memory information
CONFIG_CMD_MEMORY md, mm, nm, mw, cp, cmp, crc, base,
- loop, loopw, mtest
+ loop, loopw
+ CONFIG_CMD_MEMTEST mtest
CONFIG_CMD_MISC Misc functions like sleep etc
CONFIG_CMD_MMC * MMC memory mapped support
CONFIG_CMD_MII * MII utility commands
diff --git a/common/cmd_mem.c b/common/cmd_mem.c
index 042c994..53572f7 100644
--- a/common/cmd_mem.c
+++ b/common/cmd_mem.c
@@ -910,6 +910,7 @@ static ulong mem_test_quick(vu_long *buf, ulong start_addr, ulong end_addr,
return 0;
}
+#ifdef CONFIG_CMD_MEMTEST
/*
* Perform a memory test. A more complete alternative test can be
* configured using CONFIG_SYS_ALT_MEMTEST. The complete test loops until
@@ -1002,7 +1003,7 @@ static int do_mem_mtest(cmd_tbl_t *cmdtp, int flag, int argc,
return ret; /* not reached */
}
-
+#endif /* CONFIG_CMD_MEMTEST */
/* Modify memory.
*
@@ -1240,11 +1241,13 @@ U_BOOT_CMD(
);
#endif /* CONFIG_LOOPW */
+#ifdef CONFIG_CMD_MEMTEST
U_BOOT_CMD(
mtest, 5, 1, do_mem_mtest,
"simple RAM read/write test",
"[start [end [pattern [iterations]]]]"
);
+#endif /* CONFIG_CMD_MEMTEST */
#ifdef CONFIG_MX_CYCLIC
U_BOOT_CMD(
diff --git a/doc/README.memory-test b/doc/README.memory-test
new file mode 100644
index 0000000..eb60e8d
--- /dev/null
+++ b/doc/README.memory-test
@@ -0,0 +1,98 @@
+The most frequent cause of problems when porting U-Boot to new
+hardware, or when using a sloppy port on some board, is memory errors.
+In most cases these are not caused by failing hardware, but by
+incorrect initialization of the memory controller. So it appears to
+be a good idea to always test if the memory is working correctly,
+before looking for any other potential causes of any problems.
+
+U-Boot implements 3 different approaches to perform memory tests:
+
+1. The get_ram_size() function (see "common/memsize.c").
+
+ This function is supposed to be used in each and every U-Boot port
+ determine the presence and actual size of each of the potential
+ memory banks on this piece of hardware. The code is supposed to be
+ very fast, so running it for each reboot does not hurt. It is a
+ little known and generally underrated fact that this code will also
+ catch 99% of hardware related (i. e. reliably reproducible) memory
+ errors. It is strongly recommended to always use this function, in
+ each and every port of U-Boot.
+
+2. The "mtest" command.
+
+ This is probably the best known memory test utility in U-Boot.
+ Unfortunately, it is also the most problematic, and the most
+ useless one.
+
+ There are a number of serious problems with this command:
+
+ - It is terribly slow. Running "mtest" on the whole system RAM
+ takes a _long_ time before there is any significance in the fact
+ that no errors have been found so far.
+
+ - It is difficult to configure, and to use. And any errors here
+ will reliably crash or hang your system. "mtest" is dumb and has
+ no knowledge about memory ranges that may be in use for other
+ purposes, like exception code, U-Boot code and data, stack,
+ malloc arena, video buffer, log buffer, etc. If you let it, it
+ will happily "test" all such areas, which of course will cause
+ some problems.
+
+ - It is not easy to configure and use, and a large number of
+ systems are seriously misconfigured. The original idea was to
+ test basically the whole system RAM, with only exempting the
+ areas used by U-Boot itself - on most systems these are the areas
+ used for the exception vectors (usually at the very lower end of
+ system memory) and for U-Boot (code, data, etc. - see above;
+ these are usually at the very upper end of system memory). But
+ experience has shown that a very large number of ports use
+ pretty much bogus settings of CONFIG_SYS_MEMTEST_START and
+ CONFIG_SYS_MEMTEST_END; this results in useless tests (because
+ the ranges is too small and/or badly located) or in critical
+ failures (system crashes).
+
+ Because of these issues, the "mtest" command is considered depre-
+ cated. It should not be enabled in most normal ports of U-Boot,
+ especially not in production. If you really need a memory test,
+ then see 1. and 3. above resp. below.
+
+3. The most thorough memory test facility is available as part of the
+ POST (Power-On Self Test) sub-system, see "post/drivers/memory.c".
+
+ If you really need to perform memory tests (for example, because
+ it is mandatory part of your requirement specification), then
+ enable this test which is generic and should work on all archi-
+ tectures.
+
+WARNING:
+
+It should pointed out that _all_ these memory tests have one
+fundamental, unfixable design flaw: they are based on the assumption
+that memory errors can be found by writing to and reading from memory.
+Unfortunately, this is only true for the relatively harmless, usually
+static errors like shorts between data or address lines, unconnected
+pins, etc. All the really nasty errors which will first turn your
+hair gray, only to make you tear it out later, are dynamical errors,
+which usually happen not with simple read or write cycles on the bus,
+but when performing back-to-back data transfers in burst mode. Such
+accesses usually happen only for certain DMA operations, or for heavy
+cache use (instruction fetching, cache flushing). So far I am not
+aware of any freely available code that implements a generic, and
+efficient, memory test like that. The best known test case to stress
+a system like that is to boot Linux with root file system mounted over
+NFS, and then build some larger software package natively (say,
+compile a Linux kernel on the system) - this will cause enough context
+switches, network traffic (and thus DMA transfers from the network
+controller), varying RAM use, etc. to trigger any weak spots in this
+area.
+
+Note: An attempt was made once to implement such a test to catch
+memory problems on a specific board. The code is pretty much board
+specific (for example, it includes setting specific GPIO signals to
+provide triggers for an attached logic analyzer), but you can get an
+idea how it works: see "examples/standalone/test_burst*".
+
+Note 2: Ironically enough, the "test_burst" did not catch any RAM
+errors, not a single one ever. The problems this code was supposed
+to catch did not happen when accessing the RAM, but when reading from
+NOR flash.
diff --git a/doc/feature-removal-schedule.txt b/doc/feature-removal-schedule.txt
index e04ba2d..d9a0cc2 100644
--- a/doc/feature-removal-schedule.txt
+++ b/doc/feature-removal-schedule.txt
@@ -7,6 +7,23 @@ file.
---------------------------
+What: Remove CONFIG_CMD_MEMTEST from default list
+When: Release v2013.07
+
+Why: The "mtest" command is of little practical use (if any), and
+ experience has shown that a large number of board configu-
+ rations define useless or even dangerous start and end
+ addresses. If not even the board maintainers are able to
+ figure out which memory range can be reliably tested, how can
+ we expect such from the end users? As this problem comes up
+ repeatedly, we rather do not enable this command by default,
+ so only people who know what they are doing will be confronted
+ with it.
+
+Who: Wolfgang Denk <wd@denx.de>
+
+---------------------------
+
What: Users of the legacy miiphy_* code
When: undetermined
diff --git a/include/config_cmd_all.h b/include/config_cmd_all.h
index 0930781..53a2f05 100644
--- a/include/config_cmd_all.h
+++ b/include/config_cmd_all.h
@@ -57,7 +57,8 @@
#define CONFIG_CMD_LOADB /* loadb */
#define CONFIG_CMD_LOADS /* loads */
#define CONFIG_CMD_MEMINFO /* meminfo */
-#define CONFIG_CMD_MEMORY /* md mm nm mw cp cmp crc base loop mtest */
+#define CONFIG_CMD_MEMORY /* md mm nm mw cp cmp crc base loop */
+#define CONFIG_CMD_MEMTEST /* mtest */
#define CONFIG_CMD_MFSL /* FSL support for Microblaze */
#define CONFIG_CMD_MII /* MII support */
#define CONFIG_CMD_MISC /* Misc functions like sleep etc*/
diff --git a/include/config_cmd_default.h b/include/config_cmd_default.h
index 6e3903c..a521103 100644
--- a/include/config_cmd_default.h
+++ b/include/config_cmd_default.h
@@ -30,7 +30,8 @@
#endif
#define CONFIG_CMD_LOADB /* loadb */
#define CONFIG_CMD_LOADS /* loads */
-#define CONFIG_CMD_MEMORY /* md mm nm mw cp cmp crc base loop mtest */
+#define CONFIG_CMD_MEMORY /* md mm nm mw cp cmp crc base loop */
+#define CONFIG_CMD_MEMTEST /* mtest */
#define CONFIG_CMD_MISC /* Misc functions like sleep etc*/
#define CONFIG_CMD_NET /* bootp, tftpboot, rarpboot */
#define CONFIG_CMD_NFS /* NFS support */