Add some comments what tce.c actually does

Signed-off-by: Andi Kleen <ak@suse.de>

---
 arch/x86_64/kernel/tce.c |    2 ++
 1 files changed, 2 insertions(+)

Index: linux/arch/x86_64/kernel/tce.c
===================================================================
--- linux.orig/arch/x86_64/kernel/tce.c
+++ linux/arch/x86_64/kernel/tce.c
@@ -1,4 +1,6 @@
 /*
+ * This file manages the translation entries for the IBM Calgary IOMMU.
+ *
  * Derived from arch/powerpc/platforms/pseries/iommu.c
  *
  * Copyright (C) IBM Corporation, 2006