diff --git a/arch/alpha/include/asm/io.h b/arch/alpha/include/asm/io.h
index 4c533fc94d62f372786331cd1fe305d2c8d83f99..ccf9d65166bb621da0086624458f442fa4f6608f 100644
--- a/arch/alpha/include/asm/io.h
+++ b/arch/alpha/include/asm/io.h
@@ -513,8 +513,6 @@ extern inline void writeq(u64 b, volatile void __iomem *addr)
 #define writel_relaxed(b, addr)	__raw_writel(b, addr)
 #define writeq_relaxed(b, addr)	__raw_writeq(b, addr)
 
-#define mmiowb()
-
 /*
  * String version of IO memory access ops:
  */
diff --git a/arch/hexagon/include/asm/io.h b/arch/hexagon/include/asm/io.h
index e17262ad125e7ee0c48be297dfff08dc50f2d5e6..3d0ae09c2b8e152df0f404083ed91b87e9f126a8 100644
--- a/arch/hexagon/include/asm/io.h
+++ b/arch/hexagon/include/asm/io.h
@@ -184,8 +184,6 @@ static inline void writel(u32 data, volatile void __iomem *addr)
 #define writew_relaxed __raw_writew
 #define writel_relaxed __raw_writel
 
-#define mmiowb()
-
 /*
  * Need an mtype somewhere in here, for cache type deals?
  * This is probably too long for an inline.
diff --git a/arch/parisc/include/asm/io.h b/arch/parisc/include/asm/io.h
index 30a8315d5c0751fe448c39fc98be501e1d295271..93d37010b375c7441953cfc69ada30f1eb40979e 100644
--- a/arch/parisc/include/asm/io.h
+++ b/arch/parisc/include/asm/io.h
@@ -229,8 +229,6 @@ static inline void writeq(unsigned long long q, volatile void __iomem *addr)
 #define writel_relaxed(l, addr)	writel(l, addr)
 #define writeq_relaxed(q, addr)	writeq(q, addr)
 
-#define mmiowb() do { } while (0)
-
 void memset_io(volatile void __iomem *addr, unsigned char val, int count);
 void memcpy_fromio(void *dst, const volatile void __iomem *src, int count);
 void memcpy_toio(volatile void __iomem *dst, const void *src, int count);
diff --git a/arch/powerpc/include/asm/mmiowb.h b/arch/powerpc/include/asm/mmiowb.h
index b10180613507c080bd98ccd6fe0640f6b373b5e2..74a00127eb20416e95ec4761c088ec83bab7ae39 100644
--- a/arch/powerpc/include/asm/mmiowb.h
+++ b/arch/powerpc/include/asm/mmiowb.h
@@ -11,8 +11,6 @@
 #define arch_mmiowb_state()	(&local_paca->mmiowb_state)
 #define mmiowb()		mb()
 
-#else
-#define mmiowb()		do { } while (0)
 #endif /* CONFIG_MMIOWB */
 
 #include <asm-generic/mmiowb.h>
diff --git a/arch/sparc/include/asm/io_64.h b/arch/sparc/include/asm/io_64.h
index b162c23ae8c2305eea1ce1f8b6bb2a16aadcca24..688911051b4461b458924ab7066994d90304438f 100644
--- a/arch/sparc/include/asm/io_64.h
+++ b/arch/sparc/include/asm/io_64.h
@@ -396,8 +396,6 @@ static inline void memcpy_toio(volatile void __iomem *dst, const void *src,
 	}
 }
 
-#define mmiowb()
-
 #ifdef __KERNEL__
 
 /* On sparc64 we have the whole physical IO address space accessible
diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index bc490a7466021451cf894de31df9709cc3e3bdf6..8f3bf95a36d193c3d6526660f4eb0d381c98a6e0 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -22,10 +22,6 @@
 #include <asm/mmiowb.h>
 #include <asm-generic/pci_iomap.h>
 
-#ifndef mmiowb
-#define mmiowb() do {} while (0)
-#endif
-
 #ifndef __io_br
 #define __io_br()      barrier()
 #endif