1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 8157417724a8..b2361667839f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -781,6 +781,13 @@ and is between 256 and 4096 characters. It is defined in the file
                         bypassed by not enabling DMAR with this option. In
                         this case, gfx device will use physical address for
                         DMA.
+                forcedac [x86_64]
+                        With this option iommu will not optimize to look
+                        for io virtual address below 32 bit forcing dual
+                        address cycle on pci bus for cards supporting greater
+                        than 32 bit addressing. The default is to look
+                        for translation below 32 bit and if not available
+                        then look in the higher range.
 
         io7=            [HW] IO7 for Marvel based alpha systems
                         See comment before marvel_specify_io7 in