arm64: cmpxchg: avoid "cc" clobber in ll/sc routines

We can perform the cmpxchg comparison using eor and cbnz which avoids
the "cc" clobber for the ll/sc case and consequently for the LSE case
where we may have to fall-back on the ll/sc code at runtime.

Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h
index f89f1e4ba5772a26570da90c7143b9a9cae72dd1..c02684d1eab35c249d233080567bbd8315261001 100644 (file)
--- a/arch/arm64/include/asm/atomic_ll_sc.h
+++ b/arch/arm64/include/asm/atomic_ll_sc.h
@@ -101,14 +101,13 @@ __LL_SC_PREFIX(atomic_cmpxchg(atomic_t *ptr, int old, int new))
 
        asm volatile("// atomic_cmpxchg\n"
 "1:    ldxr    %w1, %2\n"
-"      cmp     %w1, %w3\n"
-"      b.ne    2f\n"
+"      eor     %w0, %w1, %w3\n"
+"      cbnz    %w0, 2f\n"
 "      stxr    %w0, %w4, %2\n"
 "      cbnz    %w0, 1b\n"
 "2:"
        : "=&r" (tmp), "=&r" (oldval), "+Q" (ptr->counter)
-       : "Ir" (old), "r" (new)
-       : "cc");
+       : "Lr" (old), "r" (new));
 
        smp_mb();
        return oldval;
@@ -179,14 +178,13 @@ __LL_SC_PREFIX(atomic64_cmpxchg(atomic64_t *ptr, long old, long new))
 
        asm volatile("// atomic64_cmpxchg\n"
 "1:    ldxr    %1, %2\n"
-"      cmp     %1, %3\n"
-"      b.ne    2f\n"
+"      eor     %0, %1, %3\n"
+"      cbnz    %w0, 2f\n"
 "      stxr    %w0, %4, %2\n"
 "      cbnz    %w0, 1b\n"
 "2:"
        : "=&r" (res), "=&r" (oldval), "+Q" (ptr->counter)
-       : "Ir" (old), "r" (new)
-       : "cc");
+       : "Lr" (old), "r" (new));
 
        smp_mb();
        return oldval;

diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h
index f3cb1052ab247823d301248daf3978a03e8098db..a3d21e7cee4f2efa1d023e958a977cda28f3cadc 100644 (file)
--- a/arch/arm64/include/asm/atomic_lse.h
+++ b/arch/arm64/include/asm/atomic_lse.h
@@ -166,7 +166,7 @@ static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
        "       mov     %w[ret], w30")
        : [ret] "+r" (x0), [v] "+Q" (ptr->counter)
        : [old] "r" (w1), [new] "r" (w2)
-       : "x30", "cc", "memory");
+       : "x30", "memory");
 
        return x0;
 }
@@ -313,7 +313,7 @@ static inline long atomic64_cmpxchg(atomic64_t *ptr, long old, long new)
        "       mov     %[ret], x30")
        : [ret] "+r" (x0), [v] "+Q" (ptr->counter)
        : [old] "r" (x1), [new] "r" (x2)
-       : "x30", "cc", "memory");
+       : "x30", "memory");
 
        return x0;
 }