diff --git a/include/asm-mips/smtc.h b/include/asm-mips/smtc.h
index 44dfa4a..ff3e893 100644
--- a/include/asm-mips/smtc.h
+++ b/include/asm-mips/smtc.h
@@ -55,4 +55,14 @@
 
 #define PARKED_INDEX	((unsigned int)0x80000000)
 
+/*
+ * Define low-level interrupt mask for IPIs, if necessary.
+ * By default, use SW interrupt 1, which requires no external
+ * hardware support, but which works only for single-core
+ * MIPS MT systems.
+ */
+#ifndef MIPS_CPU_IPI_IRQ
+#define MIPS_CPU_IPI_IRQ 1
+#endif
+
 #endif /*  _ASM_SMTC_MT_H */