2 files changed, 11 insertions, 3 deletions

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 4336390bcf34..1cb69e8fb0b1 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -62,7 +62,7 @@ static int __initdata dt_root_addr_cells;
 static int __initdata dt_root_size_cells;
 
 #ifdef CONFIG_PPC64
-static int __initdata iommu_is_off;
+int __initdata iommu_is_off;
 int __initdata iommu_force_on;
 unsigned long tce_alloc_start, tce_alloc_end;
 #endif
diff --git a/arch/powerpc/sysdev/dart_iommu.c b/arch/powerpc/sysdev/dart_iommu.c
index 61d317428610..38087bd6e3cf 100644
--- a/arch/powerpc/sysdev/dart_iommu.c
+++ b/arch/powerpc/sysdev/dart_iommu.c
@@ -49,6 +49,7 @@
 
 #include "dart.h"
 
+extern int iommu_is_off;
 extern int iommu_force_on;
 
 /* Physical base address and size of the DART table */
@@ -329,10 +330,17 @@ void iommu_init_early_dart(void)
 
 void __init alloc_dart_table(void)
 {
-        /* Only reserve DART space if machine has more than 2GB of RAM
+        /* Only reserve DART space if machine has more than 1GB of RAM
          * or if requested with iommu=on on cmdline.
+         *
+         * 1GB of RAM is picked as limit because some default devices
+         * (i.e. Airport Extreme) have 30 bit address range limits.
          */
-        if (lmb_end_of_DRAM() <= 0x80000000ull && !iommu_force_on)
+
+        if (iommu_is_off)
+                return;
+
+        if (!iommu_force_on && lmb_end_of_DRAM() <= 0x40000000ull)
                 return;
 
         /* 512 pages (2MB) is max DART tablesize. */