MIPS: BCM47XX: ignore last memory page

Ignoring the last page when ddr size is 128M. Cached accesses to last
page is causing the processor to prefetch using address above 128M
stepping out of the ddr address space.
Signed-off-by: NHauke Mehrtens <hauke@hauke-m.de>
Patchwork: http://patchwork.linux-mips.org/patch/4365Signed-off-by: NJohn Crispin <blogic@openwrt.org>

arch/mips/bcm47xx/prom.c

@@ -27,6 +27,7 @@
 #include <linux/types.h>
 #include <linux/kernel.h>
 #include <linux/spinlock.h>
+#include <linux/smp.h>
 #include <asm/bootinfo.h>
 #include <asm/fw/cfe/cfe_api.h>
 #include <asm/fw/cfe/cfe_error.h>
@@ -127,6 +128,7 @@ static __init void prom_init_mem(void)
 {
 	unsigned long mem;
 	unsigned long max;
+	struct cpuinfo_mips *c = &current_cpu_data;
 
 	/* Figure out memory size by finding aliases.
 	 *
@@ -155,6 +157,14 @@ static __init void prom_init_mem(void)
 			break;
 	}
 
+	/* Ignoring the last page when ddr size is 128M. Cached
+	 * accesses to last page is causing the processor to prefetch
+	 * using address above 128M stepping out of the ddr address
+	 * space.
+	 */
+	if (c->cputype == CPU_74K && (mem == (128  << 20)))
+		mem -= 0x1000;
+
 	add_memory_region(0, mem, BOOT_MEM_RAM);
 }