sh: GUSA atomic rollback support.

This implements kernel-level atomic rollback built on top of gUSA,
as an alternative non-IRQ based atomicity method. This is generally
a faster method for platforms that are lacking the LL/SC pairs that
SH-4A and later use, and is only supportable on legacy cores.

Signed-off-by: Stuart Menefy <stuart.menefy@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/include/asm-sh/cmpxchg-irq.h b/include/asm-sh/cmpxchg-irq.h
new file mode 100644
index 000000000000..43049ec0554b
--- /dev/null
+++ b/include/asm-sh/cmpxchg-irq.h
@@ -0,0 +1,40 @@
+#ifndef __ASM_SH_CMPXCHG_IRQ_H
+#define __ASM_SH_CMPXCHG_IRQ_H
+
+static inline unsigned long xchg_u32(volatile u32 *m, unsigned long val)
+{
+        unsigned long flags, retval;
+
+        local_irq_save(flags);
+        retval = *m;
+        *m = val;
+        local_irq_restore(flags);
+        return retval;
+}
+
+static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
+{
+        unsigned long flags, retval;
+
+        local_irq_save(flags);
+        retval = *m;
+        *m = val & 0xff;
+        local_irq_restore(flags);
+        return retval;
+}
+
+static inline unsigned long __cmpxchg_u32(volatile int *m, unsigned long old,
+        unsigned long new)
+{
+        __u32 retval;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        retval = *m;
+        if (retval == old)
+                *m = new;
+        local_irq_restore(flags);       /* implies memory barrier  */
+        return retval;
+}
+
+#endif /* __ASM_SH_CMPXCHG_IRQ_H */