[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, 48 insertions, 0 deletions

diff --git a/arch/i386/kernel/cpu/intel.c b/arch/i386/kernel/cpu/intel.c
index 43601de0f633..c28d26fb5f24 100644
--- 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);