diff --git a/include/asm-generic/atomic.h b/include/asm-generic/atomic.h
index 4c56e0daae9f..e37963c1df4d 100644
--- a/include/asm-generic/atomic.h
+++ b/include/asm-generic/atomic.h
@@ -16,7 +16,11 @@
 #define __ASM_GENERIC_ATOMIC_H
 
 #ifdef CONFIG_SMP
-#error not SMP safe
+/* Force people to define core atomics */
+# if !defined(atomic_add_return) || !defined(atomic_sub_return) || \
+     !defined(atomic_clear_mask) || !defined(atomic_set_mask)
+#  error "SMP requires a little arch-specific magic"
+# endif
 #endif
 
 /*
@@ -34,7 +38,9 @@
  *
  * Atomically reads the value of @v.
  */
+#ifndef atomic_read
 #define atomic_read(v)	(*(volatile int *)&(v)->counter)
+#endif
 
 /**
  * atomic_set - set atomic variable
@@ -55,6 +61,7 @@
  *
  * Atomically adds @i to @v and returns the result
  */
+#ifndef atomic_add_return
 static inline int atomic_add_return(int i, atomic_t *v)
 {
 	unsigned long flags;
@@ -68,6 +75,7 @@ static inline int atomic_add_return(int i, atomic_t *v)
 
 	return temp;
 }
+#endif
 
 /**
  * atomic_sub_return - subtract integer from atomic variable
@@ -76,6 +84,7 @@ static inline int atomic_add_return(int i, atomic_t *v)
  *
  * Atomically subtracts @i from @v and returns the result
  */
+#ifndef atomic_sub_return
 static inline int atomic_sub_return(int i, atomic_t *v)
 {
 	unsigned long flags;
@@ -89,6 +98,7 @@ static inline int atomic_sub_return(int i, atomic_t *v)
 
 	return temp;
 }
+#endif
 
 static inline int atomic_add_negative(int i, atomic_t *v)
 {
@@ -147,6 +157,7 @@ static inline int __atomic_add_unless(atomic_t *v, int a, int u)
  *
  * Atomically clears the bits set in @mask from @v
  */
+#ifndef atomic_clear_mask
 static inline void atomic_clear_mask(unsigned long mask, atomic_t *v)
 {
 	unsigned long flags;
@@ -156,6 +167,7 @@ static inline void atomic_clear_mask(unsigned long mask, atomic_t *v)
 	v->counter &= mask;
 	raw_local_irq_restore(flags);
 }
+#endif
 
 /**
  * atomic_set_mask - Atomically set bits in atomic variable
@@ -164,6 +176,7 @@ static inline void atomic_clear_mask(unsigned long mask, atomic_t *v)
  *
  * Atomically sets the bits set in @mask in @v
  */
+#ifndef atomic_set_mask
 static inline void atomic_set_mask(unsigned int mask, atomic_t *v)
 {
 	unsigned long flags;
@@ -172,6 +185,7 @@ static inline void atomic_set_mask(unsigned int mask, atomic_t *v)
 	v->counter |= mask;
 	raw_local_irq_restore(flags);
 }
+#endif
 
 /* Assume that atomic operations are already serializing */
 #define smp_mb__before_atomic_dec()	barrier()