x86-64 fixes from Andi

drivers/char/agp/Kconfig

@@ -107,7 +107,11 @@ config AGP_SWORKS
 
 config AGP_AMD_8151
 	bool "AMD 8151 support"
-	depends on AGP && !GART_IOMMU
+	depends on AGP
+	default GART_IOMMU
+	help
+	  Say Y here to support the AMD 8151 AGP bridge and the builtin
+	  GART on the AMD Athlon64/Opteron ("Hammer") CPUs.
 
 config AGP_I460
 	bool "Intel 460GX support"

drivers/char/agp/generic.c

@@ -197,6 +197,9 @@ static int agp_return_size(void)
 		break;
 	}
 
+	current_size -= (agp_memory_reserved / (1024*1024));
+	if (current_size <0)
+		current_size = 0;
 	return current_size;
 }