[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>

diff --git a/arch/i386/kernel/cpu/intel.c b/arch/i386/kernel/cpu/intel.c
index 43601de..c28d26f 100644 (file)
--- a/arch/i386/kernel/cpu/intel.c
+++ b/arch/i386/kernel/cpu/intel.c
@@ -6,6 +6,7 @@
 #include <linux/bitops.h>
 #include <linux/smp.h>
 #include <linux/thread_info.h>
+#include <linux/module.h>
 
 #include <asm/processor.h>
 #include <asm/msr.h>
@@ -264,5 +265,52 @@ __init int intel_cpu_init(void)
        return 0;
 }
 
+#ifndef CONFIG_X86_CMPXCHG
+unsigned long cmpxchg_386_u8(volatile void *ptr, u8 old, u8 new)
+{
+       u8 prev;
+       unsigned long flags;
+
+       /* Poor man's cmpxchg for 386. Unsuitable for SMP */
+       local_irq_save(flags);
+       prev = *(u8 *)ptr;
+       if (prev == old)
+               *(u8 *)ptr = new;
+       local_irq_restore(flags);
+       return prev;
+}
+EXPORT_SYMBOL(cmpxchg_386_u8);
+
+unsigned long cmpxchg_386_u16(volatile void *ptr, u16 old, u16 new)
+{
+       u16 prev;
+       unsigned long flags;
+
+       /* Poor man's cmpxchg for 386. Unsuitable for SMP */
+       local_irq_save(flags);
+       prev = *(u16 *)ptr;
+       if (prev == old)
+               *(u16 *)ptr = new;
+       local_irq_restore(flags);
+       return prev;
+}
+EXPORT_SYMBOL(cmpxchg_386_u16);
+
+unsigned long cmpxchg_386_u32(volatile void *ptr, u32 old, u32 new)
+{
+       u32 prev;
+       unsigned long flags;
+
+       /* Poor man's cmpxchg for 386. Unsuitable for SMP */
+       local_irq_save(flags);
+       prev = *(u32 *)ptr;
+       if (prev == old)
+               *(u32 *)ptr = new;
+       local_irq_restore(flags);
+       return prev;
+}
+EXPORT_SYMBOL(cmpxchg_386_u32);
+#endif
+
 // arch_initcall(intel_cpu_init);
 

diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 97d52ac..772f85d 100644 (file)
--- 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