MIPS: BCM47XX: improve memory size detection

The memory size is detected by finding a place where it repeats in
memory. Currently we are just checking when the function prom_init is
seen again, but it is better to check for a bigger part of the memory
to decrease the chance of wrong results.

This should fix a problem we saw in OpenWrt, where the detected
available memory decreed on some devices when doing a soft reboot.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: http://patchwork.linux-mips.org/patch/4362
Signed-off-by: John Crispin <blogic@openwrt.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/mips/bcm47xx/prom.c b/arch/mips/bcm47xx/prom.c
index 22258a4c652b..8c155afb1299 100644
--- a/arch/mips/bcm47xx/prom.c
+++ b/arch/mips/bcm47xx/prom.c
@@ -1,6 +1,7 @@
 /*
  *  Copyright (C) 2004 Florian Schirmer <jolt@tuxbox.org>
  *  Copyright (C) 2007 Aurelien Jarno <aurelien@aurel32.net>
+ *  Copyright (C) 2010-2012 Hauke Mehrtens <hauke@hauke-m.de>
  *
  *  This program is free software; you can redistribute  it and/or modify it
  *  under  the terms of  the GNU General  Public License as published by the
@@ -128,6 +129,7 @@ static __init void prom_init_mem(void)
 {
         unsigned long mem;
         unsigned long max;
+        unsigned long off;
         struct cpuinfo_mips *c = &current_cpu_data;
 
         /* Figure out memory size by finding aliases.
@@ -145,15 +147,15 @@ static __init void prom_init_mem(void)
          * max contains the biggest possible address supported by the platform.
          * If the method wants to try something above we assume 128MB ram.
          */
-        max = ((unsigned long)(prom_init) | ((128 << 20) - 1));
+        off = (unsigned long)prom_init;
+        max = off | ((128 << 20) - 1);
         for (mem = (1 << 20); mem < (128 << 20); mem += (1 << 20)) {
-                if (((unsigned long)(prom_init) + mem) > max) {
+                if ((off + mem) > max) {
                         mem = (128 << 20);
                         printk(KERN_DEBUG "assume 128MB RAM\n");
                         break;
                 }
-                if (*(unsigned long *)((unsigned long)(prom_init) + mem) ==
-                    *(unsigned long *)(prom_init))
+                if (!memcmp(prom_init, prom_init + mem, 32))
                         break;
         }