diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt
index 341588ec4e29c7cb3aa850f176687c6a6c1cfbc2..8d109ef67ab6bef2d0d575502308d10d5079c85c 100644
--- a/Documentation/x86/x86_64/boot-options.txt
+++ b/Documentation/x86/x86_64/boot-options.txt
@@ -236,11 +236,6 @@ IOMMU (input/output memory management unit)
     nomerge            Don't do scatter-gather (SG) merging.
     noaperture         Ask the IOMMU not to touch the aperture for AGP.
     noagp              Don't initialize the AGP driver and use full aperture.
-    allowdac           Allow double-address cycle (DAC) mode, i.e. DMA >4GB.
-                       DAC is used with 32-bit PCI to push a 64-bit address in
-                       two cycles. When off all DMA over >4GB is forced through
-                       an IOMMU or software bounce buffering.
-    nodac              Forbid DAC mode, i.e. DMA >4GB.
     panic              Always panic when IOMMU overflows.
     calgary            Use the Calgary IOMMU if it is available
 
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index b65b0d7072f179b57217167456873d280a9d16f2..b523414bc3238861625b1be7b33813b473005839 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -122,9 +122,9 @@ static __init int iommu_setup(char *p)
 		if (!strncmp(p, "forcesac", 8))
 			pr_warn("forcesac option ignored.\n");
 		if (!strncmp(p, "allowdac", 8))
-			forbid_dac = 0;
+			pr_warn("allowdac option ignored.\n");
 		if (!strncmp(p, "nodac", 5))
-			forbid_dac = 1;
+			pr_warn("nodac option ignored.\n");
 		if (!strncmp(p, "usedac", 6)) {
 			forbid_dac = -1;
 			return 1;