Index: head/sys/arm64/arm64/machdep.c
===================================================================
--- head/sys/arm64/arm64/machdep.c
+++ head/sys/arm64/arm64/machdep.c
@@ -25,6 +25,7 @@
  *
  */
 
+#include "opt_acpi.h"
 #include "opt_platform.h"
 #include "opt_ddb.h"
 
@@ -82,11 +83,19 @@
 #include <machine/vfp.h>
 #endif
 
+#ifdef DEV_ACPI
+#include <contrib/dev/acpica/include/acpi.h>
+#include <machine/acpica_machdep.h>
+#endif
+
 #ifdef FDT
 #include <dev/fdt/fdt_common.h>
 #include <dev/ofw/openfirm.h>
 #endif
 
+
+enum arm64_bus arm64_bus_method = ARM64_BUS_NONE;
+
 struct pcpu __pcpu[MAXCPU];
 
 static struct trapframe proc0_tf;
@@ -802,6 +811,61 @@
 }
 #endif
 
+static bool
+bus_probe(void)
+{
+	bool has_acpi, has_fdt;
+	char *order, *env;
+
+	has_acpi = has_fdt = false;
+
+#ifdef FDT
+	has_fdt = (OF_peer(0) != 0);
+#endif
+#ifdef DEV_ACPI
+	has_acpi = (acpi_find_table(ACPI_SIG_SPCR) != 0);
+#endif
+
+	env = kern_getenv("kern.cfg.order");
+	if (env != NULL) {
+		order = env;
+		while (order != NULL) {
+			if (has_acpi &&
+			    strncmp(order, "acpi", 4) == 0 &&
+			    (order[4] == ',' || order[4] == '\0')) {
+				arm64_bus_method = ARM64_BUS_ACPI;
+				break;
+			}
+			if (has_fdt &&
+			    strncmp(order, "fdt", 3) == 0 &&
+			    (order[3] == ',' || order[3] == '\0')) {
+				arm64_bus_method = ARM64_BUS_FDT;
+				break;
+			}
+			order = strchr(order, ',');
+		}
+		freeenv(env);
+
+		/* If we set the bus method it is valid */
+		if (arm64_bus_method != ARM64_BUS_NONE)
+			return (true);
+	}
+	/* If no order or an invalid order was set use the default */
+	if (arm64_bus_method == ARM64_BUS_NONE) {
+		if (has_fdt)
+			arm64_bus_method = ARM64_BUS_FDT;
+		else if (has_acpi)
+			arm64_bus_method = ARM64_BUS_ACPI;
+	}
+
+	/*
+	 * If no option was set the default is valid, otherwise we are
+	 * setting one to get cninit() working, then calling panic to tell
+	 * the user about the invalid bus setup.
+	 */
+	return (env == NULL);
+}
+
 static void
 cache_setup(void)
 {
@@ -849,6 +913,7 @@
 	vm_offset_t lastaddr;
 	caddr_t kmdp;
 	vm_paddr_t mem_len;
+	bool valid;
 	int i;
 
 	/* Set the module data location */
@@ -921,8 +986,14 @@
 
 	devmap_bootstrap(0, NULL);
 
+	valid = bus_probe();
+
 	cninit();
 
+	if (!valid)
+		panic("Invalid bus configuration: %s",
+		    kern_getenv("kern.cfg.order"));
+
 	init_proc0(abp->kern_stack);
 	msgbufinit(msgbufp, msgbufsize);
 	mutex_init();
Index: head/sys/arm64/arm64/mp_machdep.c
===================================================================
--- head/sys/arm64/arm64/mp_machdep.c
+++ head/sys/arm64/arm64/mp_machdep.c
@@ -52,6 +52,7 @@
 #include <vm/vm_kern.h>
 
 #include <machine/debug_monitor.h>
+#include <machine/machdep.h>
 #include <machine/intr.h>
 #include <machine/smp.h>
 #ifdef VFP
@@ -90,13 +91,6 @@
 
 extern struct pcpu __pcpu[];
 
-static enum {
-	CPUS_UNKNOWN,
-#ifdef FDT
-	CPUS_FDT,
-#endif
-} cpu_enum_method;
-
 static device_identify_t arm64_cpu_identify;
 static device_probe_t arm64_cpu_probe;
 static device_attach_t arm64_cpu_attach;
@@ -499,14 +493,14 @@
 
 	CPU_SET(0, &all_cpus);
 
-	switch(cpu_enum_method) {
+	switch(arm64_bus_method) {
 #ifdef FDT
-	case CPUS_FDT:
+	case ARM64_BUS_FDT:
 		KASSERT(cpu0 >= 0, ("Current CPU was not found"));
 		ofw_cpu_early_foreach(cpu_init_fdt, true);
 		break;
 #endif
-	case CPUS_UNKNOWN:
+	default:
 		break;
 	}
 }
@@ -544,15 +538,17 @@
 #ifdef FDT
 	int cores;
 
-	cores = ofw_cpu_early_foreach(cpu_find_cpu0_fdt, false);
-	if (cores > 0) {
-		cores = MIN(cores, MAXCPU);
-		if (bootverbose)
-			printf("Found %d CPUs in the device tree\n", cores);
-		mp_ncpus = cores;
-		mp_maxid = cores - 1;
-		cpu_enum_method = CPUS_FDT;
-		return;
+	if (arm64_bus_method == ARM64_BUS_FDT) {
+		cores = ofw_cpu_early_foreach(cpu_find_cpu0_fdt, false);
+		if (cores > 0) {
+			cores = MIN(cores, MAXCPU);
+			if (bootverbose)
+				printf("Found %d CPUs in the device tree\n",
+				    cores);
+			mp_ncpus = cores;
+			mp_maxid = cores - 1;
+			return;
+		}
 	}
 #endif
 
Index: head/sys/arm64/arm64/nexus.c
===================================================================
--- head/sys/arm64/arm64/nexus.c
+++ head/sys/arm64/arm64/nexus.c
@@ -55,6 +55,7 @@
 #include <sys/rman.h>
 #include <sys/interrupt.h>
 
+#include <machine/machdep.h>
 #include <machine/vmparam.h>
 #include <machine/pcb.h>
 #include <vm/vm.h>
@@ -411,7 +412,7 @@
 nexus_fdt_probe(device_t dev)
 {
 
-	if (OF_peer(0) == 0)
+	if (arm64_bus_method != ARM64_BUS_FDT)
 		return (ENXIO);
 
 	device_quiet(dev);
@@ -455,7 +456,7 @@
 nexus_acpi_probe(device_t dev)
 {
 
-	if (acpi_identify() != 0)
+	if (arm64_bus_method != ARM64_BUS_ACPI || acpi_identify() != 0)
 		return (ENXIO);
 
 	device_quiet(dev);
Index: head/sys/arm64/include/machdep.h
===================================================================
--- head/sys/arm64/include/machdep.h
+++ head/sys/arm64/include/machdep.h
@@ -37,6 +37,14 @@
 	vm_offset_t	kern_l0pt;	/* L1 page table for the kernel */
 };
 
+enum arm64_bus {
+	ARM64_BUS_NONE,
+	ARM64_BUS_FDT,
+	ARM64_BUS_ACPI,
+};
+
+extern enum arm64_bus arm64_bus_method;
+
 extern vm_paddr_t physmap[];
 extern u_int physmap_idx;