diff --git a/sys/arm/arm/busdma_machdep.c b/sys/arm/arm/busdma_machdep.c
--- a/sys/arm/arm/busdma_machdep.c
+++ b/sys/arm/arm/busdma_machdep.c
@@ -375,41 +375,6 @@
 	return (0);
 }
 
-/*
- * Convenience function for manipulating driver locks from busdma (during
- * busdma_swi, for example).
- */
-void
-busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
-{
-	struct mtx *dmtx;
-
-	dmtx = (struct mtx *)arg;
-	switch (op) {
-	case BUS_DMA_LOCK:
-		mtx_lock(dmtx);
-		break;
-	case BUS_DMA_UNLOCK:
-		mtx_unlock(dmtx);
-		break;
-	default:
-		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
-	}
-}
-
-/*
- * dflt_lock should never get called.  It gets put into the dma tag when
- * lockfunc == NULL, which is only valid if the maps that are associated
- * with the tag are meant to never be defered.
- * XXX Should have a way to identify which driver is responsible here.
- */
-static void
-dflt_lock(void *arg, bus_dma_lock_op_t op)
-{
-
-	panic("driver error: busdma dflt_lock called");
-}
-
 /*
  * Allocate a device specific dma_tag.
  */
@@ -461,7 +426,7 @@
 		newtag->lockfunc = lockfunc;
 		newtag->lockfuncarg = lockfuncarg;
 	} else {
-		newtag->lockfunc = dflt_lock;
+		newtag->lockfunc = _busdma_dflt_lock;
 		newtag->lockfuncarg = NULL;
 	}
 
diff --git a/sys/arm64/arm64/busdma_machdep.c b/sys/arm64/arm64/busdma_machdep.c
--- a/sys/arm64/arm64/busdma_machdep.c
+++ b/sys/arm64/arm64/busdma_machdep.c
@@ -51,41 +51,6 @@
 #include <machine/bus.h>
 #include <arm64/include/bus_dma_impl.h>
 
-/*
- * Convenience function for manipulating driver locks from busdma (during
- * busdma_swi, for example).
- */
-void
-busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
-{
-	struct mtx *dmtx;
-
-	dmtx = (struct mtx *)arg;
-	switch (op) {
-	case BUS_DMA_LOCK:
-		mtx_lock(dmtx);
-		break;
-	case BUS_DMA_UNLOCK:
-		mtx_unlock(dmtx);
-		break;
-	default:
-		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
-	}
-}
-
-/*
- * dflt_lock should never get called.  It gets put into the dma tag when
- * lockfunc == NULL, which is only valid if the maps that are associated
- * with the tag are meant to never be defered.
- * XXX Should have a way to identify which driver is responsible here.
- */
-void
-bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op)
-{
-
-	panic("driver error: busdma dflt_lock called");
-}
-
 /*
  * Return true if a match is made.
  *
@@ -154,7 +119,7 @@
 		common->lockfunc = lockfunc;
 		common->lockfuncarg = lockfuncarg;
 	} else {
-		common->lockfunc = bus_dma_dflt_lock;
+		common->lockfunc = _busdma_dflt_lock;
 		common->lockfuncarg = NULL;
 	}
 
diff --git a/sys/arm64/include/bus_dma_impl.h b/sys/arm64/include/bus_dma_impl.h
--- a/sys/arm64/include/bus_dma_impl.h
+++ b/sys/arm64/include/bus_dma_impl.h
@@ -84,7 +84,6 @@
 	    bus_dmasync_op_t op);
 };
 
-void bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op);
 int bus_dma_run_filter(struct bus_dma_tag_common *dmat, bus_addr_t paddr);
 int common_bus_dma_tag_create(struct bus_dma_tag_common *parent,
     bus_size_t alignment,
diff --git a/sys/kern/subr_bus_dma.c b/sys/kern/subr_bus_dma.c
--- a/sys/kern/subr_bus_dma.c
+++ b/sys/kern/subr_bus_dma.c
@@ -42,8 +42,10 @@
 #include <sys/bus.h>
 #include <sys/callout.h>
 #include <sys/ktr.h>
+#include <sys/lock.h>
 #include <sys/mbuf.h>
 #include <sys/memdesc.h>
+#include <sys/mutex.h>
 #include <sys/proc.h>
 #include <sys/uio.h>
 
@@ -59,6 +61,43 @@
 
 #include <machine/bus.h>
 
+/*
+ * Convenience function for manipulating driver locks from busdma (during
+ * busdma_swi, for example).
+ */
+void
+busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
+{
+	struct mtx *dmtx;
+
+	dmtx = (struct mtx *)arg;
+	switch (op) {
+	case BUS_DMA_LOCK:
+		mtx_lock(dmtx);
+		break;
+	case BUS_DMA_UNLOCK:
+		mtx_unlock(dmtx);
+		break;
+	default:
+		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
+	}
+}
+
+/*
+ * dflt_lock should never get called.  It gets put into the dma tag when
+ * lockfunc == NULL, which is only valid if the maps that are associated
+ * with the tag are meant to never be deferred.
+ *
+ * XXX Should have a way to identify which driver is responsible here.
+ */
+void
+_busdma_dflt_lock(void *arg, bus_dma_lock_op_t op)
+{
+
+	panic("driver error: _bus_dma_dflt_lock called");
+}
+
+
 /*
  * Load up data starting at offset within a region specified by a
  * list of virtual address ranges until either length or the region
diff --git a/sys/powerpc/powerpc/busdma_machdep.c b/sys/powerpc/powerpc/busdma_machdep.c
--- a/sys/powerpc/powerpc/busdma_machdep.c
+++ b/sys/powerpc/powerpc/busdma_machdep.c
@@ -146,40 +146,6 @@
 	return (retval);
 }
 
-/*
- * Convenience function for manipulating driver locks from busdma (during
- * busdma_swi, for example).
- */
-void
-busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
-{
-	struct mtx *dmtx;
-
-	dmtx = (struct mtx *)arg;
-	switch (op) {
-	case BUS_DMA_LOCK:
-		mtx_lock(dmtx);
-		break;
-	case BUS_DMA_UNLOCK:
-		mtx_unlock(dmtx);
-		break;
-	default:
-		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
-	}
-}
-
-/*
- * dflt_lock should never get called.  It gets put into the dma tag when
- * lockfunc == NULL, which is only valid if the maps that are associated
- * with the tag are meant to never be defered.
- * XXX Should have a way to identify which driver is responsible here.
- */
-static void
-dflt_lock(void *arg, bus_dma_lock_op_t op)
-{
-	panic("driver error: busdma dflt_lock called");
-}
-
 #define BUS_DMA_COULD_BOUNCE	BUS_DMA_BUS3
 #define BUS_DMA_MIN_ALLOC_COMP	BUS_DMA_BUS4
 /*
@@ -232,7 +198,7 @@
 		newtag->lockfunc = lockfunc;
 		newtag->lockfuncarg = lockfuncarg;
 	} else {
-		newtag->lockfunc = dflt_lock;
+		newtag->lockfunc = _busdma_dflt_lock;
 		newtag->lockfuncarg = NULL;
 	}
 
diff --git a/sys/riscv/include/bus_dma_impl.h b/sys/riscv/include/bus_dma_impl.h
--- a/sys/riscv/include/bus_dma_impl.h
+++ b/sys/riscv/include/bus_dma_impl.h
@@ -81,7 +81,6 @@
 	    bus_dmasync_op_t op);
 };
 
-void bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op);
 int bus_dma_run_filter(struct bus_dma_tag_common *dmat, bus_addr_t paddr);
 int common_bus_dma_tag_create(struct bus_dma_tag_common *parent,
     bus_size_t alignment,
diff --git a/sys/riscv/riscv/busdma_machdep.c b/sys/riscv/riscv/busdma_machdep.c
--- a/sys/riscv/riscv/busdma_machdep.c
+++ b/sys/riscv/riscv/busdma_machdep.c
@@ -51,41 +51,6 @@
 #include <machine/bus.h>
 #include <machine/bus_dma_impl.h>
 
-/*
- * Convenience function for manipulating driver locks from busdma (during
- * busdma_swi, for example).
- */
-void
-busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
-{
-	struct mtx *dmtx;
-
-	dmtx = (struct mtx *)arg;
-	switch (op) {
-	case BUS_DMA_LOCK:
-		mtx_lock(dmtx);
-		break;
-	case BUS_DMA_UNLOCK:
-		mtx_unlock(dmtx);
-		break;
-	default:
-		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
-	}
-}
-
-/*
- * dflt_lock should never get called.  It gets put into the dma tag when
- * lockfunc == NULL, which is only valid if the maps that are associated
- * with the tag are meant to never be defered.
- * XXX Should have a way to identify which driver is responsible here.
- */
-void
-bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op)
-{
-
-	panic("driver error: busdma dflt_lock called");
-}
-
 /*
  * Return true if a match is made.
  *
@@ -156,7 +121,7 @@
 		common->lockfunc = lockfunc;
 		common->lockfuncarg = lockfuncarg;
 	} else {
-		common->lockfunc = bus_dma_dflt_lock;
+		common->lockfunc = _busdma_dflt_lock;
 		common->lockfuncarg = NULL;
 	}
 
diff --git a/sys/sys/bus_dma.h b/sys/sys/bus_dma.h
--- a/sys/sys/bus_dma.h
+++ b/sys/sys/bus_dma.h
@@ -149,6 +149,11 @@
  */
 void busdma_lock_mutex(void *arg, bus_dma_lock_op_t op);
 
+/*
+ * Internal helper function used by tags that do not defer loads.
+ */
+void _busdma_dflt_lock(void *arg, bus_dma_lock_op_t op);
+
 /*
  * Allocate a device specific dma_tag encapsulating the constraints of
  * the parent tag in addition to other restrictions specified:
diff --git a/sys/x86/include/busdma_impl.h b/sys/x86/include/busdma_impl.h
--- a/sys/x86/include/busdma_impl.h
+++ b/sys/x86/include/busdma_impl.h
@@ -89,7 +89,6 @@
 #endif
 };
 
-void bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op);
 int bus_dma_run_filter(struct bus_dma_tag_common *dmat, vm_paddr_t paddr);
 int common_bus_dma_tag_create(struct bus_dma_tag_common *parent,
     bus_size_t alignment,
diff --git a/sys/x86/x86/busdma_machdep.c b/sys/x86/x86/busdma_machdep.c
--- a/sys/x86/x86/busdma_machdep.c
+++ b/sys/x86/x86/busdma_machdep.c
@@ -55,41 +55,6 @@
 #include <machine/bus.h>
 #include <x86/include/busdma_impl.h>
 
-/*
- * Convenience function for manipulating driver locks from busdma (during
- * busdma_swi, for example).
- */
-void
-busdma_lock_mutex(void *arg, bus_dma_lock_op_t op)
-{
-	struct mtx *dmtx;
-
-	dmtx = (struct mtx *)arg;
-	switch (op) {
-	case BUS_DMA_LOCK:
-		mtx_lock(dmtx);
-		break;
-	case BUS_DMA_UNLOCK:
-		mtx_unlock(dmtx);
-		break;
-	default:
-		panic("Unknown operation 0x%x for busdma_lock_mutex!", op);
-	}
-}
-
-/*
- * dflt_lock should never get called.  It gets put into the dma tag when
- * lockfunc == NULL, which is only valid if the maps that are associated
- * with the tag are meant to never be defered.
- * XXX Should have a way to identify which driver is responsible here.
- */
-void
-bus_dma_dflt_lock(void *arg, bus_dma_lock_op_t op)
-{
-
-	panic("driver error: busdma dflt_lock called");
-}
-
 /*
  * Return true if a match is made.
  *
@@ -161,7 +126,7 @@
 		common->lockfunc = lockfunc;
 		common->lockfuncarg = lockfuncarg;
 	} else {
-		common->lockfunc = bus_dma_dflt_lock;
+		common->lockfunc = _busdma_dflt_lock;
 		common->lockfuncarg = NULL;
 	}