Index: sys/arm64/iommu/smmu.c
===================================================================
--- sys/arm64/iommu/smmu.c
+++ sys/arm64/iommu/smmu.c
@@ -138,6 +138,8 @@
 
 #define	SMMU_Q_ALIGN		(64 * 1024)
 
+#define	SMMU_POLL_TIMEOUT_US	1000000
+
 static struct resource_spec smmu_spec[] = {
 	{ SYS_RES_MEMORY, 0, RF_ACTIVE },
 	{ SYS_RES_IRQ, 0, RF_ACTIVE },
@@ -279,7 +281,7 @@
 	uint32_t v;
 	int timeout;
 
-	timeout = 100000;
+	timeout = SMMU_POLL_TIMEOUT_US;
 
 	bus_write_4(sc->res[0], reg, val);
 
@@ -287,6 +289,7 @@
 		v = bus_read_4(sc->res[0], reg_ack);
 		if (v == val)
 			break;
+		DELAY(1);
 	} while (timeout--);
 
 	if (timeout <= 0) {