diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index a5c539fa5d2bc03ba233f4d11de1b64d839990ab..34b643227df16ee41b19e7e2e70459268f9b1b2b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -30,6 +30,7 @@
 #define IOMMU_WRITE	(1 << 1)
 #define IOMMU_CACHE	(1 << 2) /* DMA cache coherency */
 #define IOMMU_NOEXEC	(1 << 3)
+#define IOMMU_MMIO	(1 << 4) /* e.g. things like MSI doorbells */
 
 struct iommu_ops;
 struct iommu_group;