[PATCH] i386: generic cmpxchg

- Make cmpxchg generally available on the i386 platform.

- Provide emulation of cmpxchg suitable for uniprocessor if built and run on
  386.

From: Christoph Lameter <clameter@sgi.com>

- Cut down patch and small style changes.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 39 insertions, 3 deletions

diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 97d52ac49e46..772f85da1206 100644
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -263,6 +263,10 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz
 
 #ifdef CONFIG_X86_CMPXCHG
 #define __HAVE_ARCH_CMPXCHG 1
+#define cmpxchg(ptr,o,n)\
+        ((__typeof__(*(ptr)))__cmpxchg((ptr),(unsigned long)(o),\
+                                        (unsigned long)(n),sizeof(*(ptr))))
+#endif
 
 static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
                                       unsigned long new, int size)
@@ -291,10 +295,42 @@ static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
         return old;
 }
 
-#define cmpxchg(ptr,o,n)\
-        ((__typeof__(*(ptr)))__cmpxchg((ptr),(unsigned long)(o),\
-                                        (unsigned long)(n),sizeof(*(ptr))))
+#ifndef CONFIG_X86_CMPXCHG
+/*
+ * Building a kernel capable running on 80386. It may be necessary to
+ * simulate the cmpxchg on the 80386 CPU. For that purpose we define
+ * a function for each of the sizes we support.
+ */
 
+extern unsigned long cmpxchg_386_u8(volatile void *, u8, u8);
+extern unsigned long cmpxchg_386_u16(volatile void *, u16, u16);
+extern unsigned long cmpxchg_386_u32(volatile void *, u32, u32);
+
+static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
+                                      unsigned long new, int size)
+{
+        switch (size) {
+        case 1:
+                return cmpxchg_386_u8(ptr, old, new);
+        case 2:
+                return cmpxchg_386_u16(ptr, old, new);
+        case 4:
+                return cmpxchg_386_u32(ptr, old, new);
+        }
+        return old;
+}
+
+#define cmpxchg(ptr,o,n)                                                \
+({                                                                      \
+        __typeof__(*(ptr)) __ret;                                       \
+        if (likely(boot_cpu_data.x86 > 3))                              \
+                __ret = __cmpxchg((ptr), (unsigned long)(o),            \
+                                        (unsigned long)(n), sizeof(*(ptr))); \
+        else                                                            \
+                __ret = cmpxchg_386((ptr), (unsigned long)(o),          \
+                                        (unsigned long)(n), sizeof(*(ptr))); \
+        __ret;                                                          \
+})
 #endif
 
 #ifdef CONFIG_X86_CMPXCHG64