diff --git a/sys/arm/arm/machdep.c b/sys/arm/arm/machdep.c
--- a/sys/arm/arm/machdep.c
+++ b/sys/arm/arm/machdep.c
@@ -134,6 +134,14 @@
 static void *delay_arg;
 #endif
 
+#if defined(SOCDEV_PA)
+#if !defined(SOCDEV_VA)
+#error SOCDEV_PA defined, but not SOCDEV_VA
+#endif
+uintptr_t socdev_va = SOCDEV_VA;
+#endif
+
+
 struct kva_md_info kmi;
 /*
  * arm32_vector_init:
diff --git a/sys/arm/include/machdep.h b/sys/arm/include/machdep.h
--- a/sys/arm/include/machdep.h
+++ b/sys/arm/include/machdep.h
@@ -51,6 +51,13 @@
     struct mem_region *mr, int *mrcnt);
 #endif
 
+#ifdef SOCDEV_PA
+/*
+ * The virtual address SOCDEV_PA is mapped at.
+ */
+extern uintptr_t socdev_va;
+#endif
+
 /*
  * Symbols created by ldscript.arm which are accessible in the kernel as global
  * symbols. They have uint8 type because they mark the byte location where the
diff --git a/sys/arm64/arm64/machdep.c b/sys/arm64/arm64/machdep.c
--- a/sys/arm64/arm64/machdep.c
+++ b/sys/arm64/arm64/machdep.c
@@ -138,6 +138,15 @@
 int64_t dczva_line_size;	/* The size of cache line the dc zva zeroes */
 int has_pan;
 
+#if defined(SOCDEV_PA)
+/*
+ * This is the virtual address used to access SOCDEV_PA. As it's set before
+ * .bss is cleared we need to ensure it's preserved. To do this use
+ * __read_mostly as it's only ever set once but read in the putc functions.
+ */
+uintptr_t socdev_va __read_mostly;
+#endif
+
 /*
  * Physical address of the EFI System Table. Stashed from the metadata hints
  * passed into the kernel and used by the EFI code to call runtime services.