powerpc/mm: Add pte_xchg() helper

We have five locations in 64-bit hash MMU code that do a cmpxchg() of a
PTE. Currently doing it inline OK, but in a future patch we will be
converting the PTEs to __be64 in some configs. In that case we will need
casts at every cmpxchg() site in order to keep sparse happy.

So move the logic into a helper, this is a reasonably nice cleanup on
its own.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/pgtable-types.h b/arch/powerpc/include/asm/pgtable-types.h
index 1464e74178d8..e7f4f3e0fcde 100644
--- a/arch/powerpc/include/asm/pgtable-types.h
+++ b/arch/powerpc/include/asm/pgtable-types.h
@@ -54,4 +54,16 @@ typedef struct { pte_t pte; unsigned long hidx; } real_pte_t;
 #else
 typedef struct { pte_t pte; } real_pte_t;
 #endif
+
+#ifdef CONFIG_PPC_STD_MMU_64
+#include <asm/cmpxchg.h>
+
+static inline bool pte_xchg(pte_t *ptep, pte_t old, pte_t new)
+{
+	unsigned long *p = (unsigned long *)ptep;
+
+	return pte_val(old) == __cmpxchg_u64(p, pte_val(old), pte_val(new));
+}
+#endif
+
 #endif /* _ASM_POWERPC_PGTABLE_TYPES_H */