o Add machine/iommu.h and include MD iommu headers from it,

so we don't ifdef for every arch in busdma_iommu.c;
o No need to include specialreg.h for x86, remove it.

Requested by:	andrew
Reviewed by:	kib
Sponsored by:	DARPA/AFRL
Differential Revision:	https://reviews.freebsd.org/D25957

sys/amd64/include/iommu.h

@@ -0,0 +1,6 @@
+/*-
+ * This file is in the public domain.
+ */
+/* $FreeBSD$ */
+
+#include <x86/iommu.h>

sys/dev/iommu/busdma_iommu.c

@@ -59,17 +59,12 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_object.h>
 #include <vm/vm_page.h>
 #include <vm/vm_map.h>
+#include <dev/iommu/iommu.h>
 #include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
-#if defined(__amd64__) || defined(__i386__)
-#include <machine/specialreg.h>
-#include <x86/include/busdma_impl.h>
-#include <x86/iommu/intel_reg.h>
+#include <machine/iommu.h>
 #include <dev/iommu/busdma_iommu.h>
-#include <dev/iommu/iommu.h>
-#include <x86/iommu/intel_dmar.h>
-#endif
 
 /*
  * busdma_iommu.c, the implementation of the busdma(9) interface using

sys/dev/iommu/iommu_gas.c

@@ -65,9 +65,7 @@ __FBSDID("$FreeBSD$");
 #include <machine/atomic.h>
 #include <machine/bus.h>
 #include <machine/md_var.h>
-#if defined(__amd64__) || defined(__i386__)
-#include <x86/iommu/intel_reg.h>
-#endif
+#include <machine/iommu.h>
 #include <dev/iommu/busdma_iommu.h>
 
 /*

sys/i386/include/iommu.h

@@ -0,0 +1,6 @@
+/*-
+ * This file is in the public domain.
+ */
+/* $FreeBSD$ */
+
+#include <x86/iommu.h>

sys/x86/include/iommu.h

@@ -0,0 +1,13 @@
+/*-
+ * This file is in the public domain.
+ */
+/* $FreeBSD$ */
+
+#ifndef	_MACHINE_IOMMU_H_
+#define	_MACHINE_IOMMU_H_
+
+#include <x86/include/busdma_impl.h>
+#include <x86/iommu/intel_reg.h>
+#include <x86/iommu/intel_dmar.h>
+
+#endif /* !_MACHINE_IOMMU_H_ */