diff --git a/include/lib/extensions/sme.h b/include/lib/extensions/sme.h
new file mode 100644
index 0000000..893f9f2
--- /dev/null
+++ b/include/lib/extensions/sme.h
@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef SME_H
+#define SME_H
+
+#include <stdbool.h>
+
+#include <context.h>
+
+/*
+ * Maximum value of LEN field in SMCR_ELx. This is different than the maximum
+ * supported value which is platform dependent. In the first version of SME the
+ * LEN field is limited to 4 bits but will be expanded in future iterations.
+ * To support different versions, the code that discovers the supported vector
+ * lengths will write the max value into SMCR_ELx then read it back to see how
+ * many bits are implemented.
+ */
+#define SME_SMCR_LEN_MAX	U(0x1FF)
+
+void sme_enable(cpu_context_t *context);
+void sme_disable(cpu_context_t *context);
+
+#endif /* SME_H */
diff --git a/include/lib/extensions/sve.h b/include/lib/extensions/sve.h
index c85e08c..4b66cdb 100644
--- a/include/lib/extensions/sve.h
+++ b/include/lib/extensions/sve.h
@@ -10,5 +10,6 @@
 #include <context.h>
 
 void sve_enable(cpu_context_t *context);
+void sve_disable(cpu_context_t *context);
 
 #endif /* SVE_H */