static int __init parse_amd_iommu_size_options(char *str)
 {
-       for (; *str; ++str) {
-               if (strcmp(str, "32M") == 0)
-                       amd_iommu_aperture_order = 25;
-               if (strcmp(str, "64M") == 0)
-                       amd_iommu_aperture_order = 26;
-               if (strcmp(str, "128M") == 0)
-                       amd_iommu_aperture_order = 27;
-               if (strcmp(str, "256M") == 0)
-                       amd_iommu_aperture_order = 28;
-               if (strcmp(str, "512M") == 0)
-                       amd_iommu_aperture_order = 29;
-               if (strcmp(str, "1G") == 0)
-                       amd_iommu_aperture_order = 30;
-       }
+       unsigned order = PAGE_SHIFT + get_order(memparse(str, &str));
+
+       if ((order > 24) && (order < 31))
+               amd_iommu_aperture_order = order;
 
        return 1;
 }