arm64: atomics: avoid out-of-line ll/sc atomics

When building for LSE atomics (CONFIG_ARM64_LSE_ATOMICS), if the hardware
or toolchain doesn't support it the existing code will fallback to ll/sc
atomics. It achieves this by branching from inline assembly to a function
that is built with special compile flags. Further this results in the
clobbering of registers even when the fallback isn't used increasing
register pressure.

Improve this by providing inline implementations of both LSE and
ll/sc and use a static key to select between them, which allows for the
compiler to generate better atomics code. Put the LL/SC fallback atomics
in their own subsection to improve icache performance.

Signed-off-by: Andrew Murray <[email protected]>
Signed-off-by: Will Deacon <[email protected]>

Author: Andrew Murray

arch/arm64/include/asm/atomic.h

@@ -17,16 +17,7 @@
 
 #ifdef __KERNEL__
 
-#define __ARM64_IN_ATOMIC_IMPL
-
-#if defined(CONFIG_ARM64_LSE_ATOMICS) && defined(CONFIG_AS_LSE)
-#include <asm/atomic_lse.h>
-#else
-#include <asm/atomic_ll_sc.h>
-#endif
-
-#undef __ARM64_IN_ATOMIC_IMPL
-
+#include <asm/atomic_arch.h>
 #include <asm/cmpxchg.h>
 
 #define ATOMIC_INIT(i)	{ (i) }

arch/arm64/include/asm/atomic_arch.h

@@ -0,0 +1,155 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Selection between LSE and LL/SC atomics.
+ *
+ * Copyright (C) 2018 ARM Ltd.
+ * Author: Andrew Murray <[email protected]>
+ */
+
+#ifndef __ASM_ATOMIC_ARCH_H
+#define __ASM_ATOMIC_ARCH_H
+
+
+#include <linux/jump_label.h>
+
+#include <asm/cpucaps.h>
+#include <asm/atomic_ll_sc.h>
+#include <asm/atomic_lse.h>
+
+extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
+extern struct static_key_false arm64_const_caps_ready;
+
+static inline bool system_uses_lse_atomics(void)
+{
+	return (IS_ENABLED(CONFIG_ARM64_LSE_ATOMICS) &&
+		IS_ENABLED(CONFIG_AS_LSE) &&
+		static_branch_likely(&arm64_const_caps_ready)) &&
+		static_branch_likely(&cpu_hwcap_keys[ARM64_HAS_LSE_ATOMICS]);
+}
+
+#define __lse_ll_sc_body(op, ...)					\
+({									\
+	system_uses_lse_atomics() ?					\
+		__lse_##op(__VA_ARGS__) :				\
+		__ll_sc_##op(__VA_ARGS__);				\
+})
+
+#define ATOMIC_OP(op)							\
+static inline void arch_##op(int i, atomic_t *v)			\
+{									\
+	__lse_ll_sc_body(op, i, v);					\
+}
+
+ATOMIC_OP(atomic_andnot)
+ATOMIC_OP(atomic_or)
+ATOMIC_OP(atomic_xor)
+ATOMIC_OP(atomic_add)
+ATOMIC_OP(atomic_and)
+ATOMIC_OP(atomic_sub)
+
+
+#define ATOMIC_FETCH_OP(name, op)					\
+static inline int arch_##op##name(int i, atomic_t *v)			\
+{									\
+	return __lse_ll_sc_body(op##name, i, v);			\
+}
+
+#define ATOMIC_FETCH_OPS(op)						\
+	ATOMIC_FETCH_OP(_relaxed, op)					\
+	ATOMIC_FETCH_OP(_acquire, op)					\
+	ATOMIC_FETCH_OP(_release, op)					\
+	ATOMIC_FETCH_OP(        , op)
+
+ATOMIC_FETCH_OPS(atomic_fetch_andnot)
+ATOMIC_FETCH_OPS(atomic_fetch_or)
+ATOMIC_FETCH_OPS(atomic_fetch_xor)
+ATOMIC_FETCH_OPS(atomic_fetch_add)
+ATOMIC_FETCH_OPS(atomic_fetch_and)
+ATOMIC_FETCH_OPS(atomic_fetch_sub)
+ATOMIC_FETCH_OPS(atomic_add_return)
+ATOMIC_FETCH_OPS(atomic_sub_return)
+
+
+#define ATOMIC64_OP(op)							\
+static inline void arch_##op(long i, atomic64_t *v)			\
+{									\
+	__lse_ll_sc_body(op, i, v);					\
+}
+
+ATOMIC64_OP(atomic64_andnot)
+ATOMIC64_OP(atomic64_or)
+ATOMIC64_OP(atomic64_xor)
+ATOMIC64_OP(atomic64_add)
+ATOMIC64_OP(atomic64_and)
+ATOMIC64_OP(atomic64_sub)
+
+
+#define ATOMIC64_FETCH_OP(name, op)					\
+static inline long arch_##op##name(long i, atomic64_t *v)		\
+{									\
+	return __lse_ll_sc_body(op##name, i, v);			\
+}
+
+#define ATOMIC64_FETCH_OPS(op)						\
+	ATOMIC64_FETCH_OP(_relaxed, op)					\
+	ATOMIC64_FETCH_OP(_acquire, op)					\
+	ATOMIC64_FETCH_OP(_release, op)					\
+	ATOMIC64_FETCH_OP(        , op)
+
+ATOMIC64_FETCH_OPS(atomic64_fetch_andnot)
+ATOMIC64_FETCH_OPS(atomic64_fetch_or)
+ATOMIC64_FETCH_OPS(atomic64_fetch_xor)
+ATOMIC64_FETCH_OPS(atomic64_fetch_add)
+ATOMIC64_FETCH_OPS(atomic64_fetch_and)
+ATOMIC64_FETCH_OPS(atomic64_fetch_sub)
+ATOMIC64_FETCH_OPS(atomic64_add_return)
+ATOMIC64_FETCH_OPS(atomic64_sub_return)
+
+
+static inline long arch_atomic64_dec_if_positive(atomic64_t *v)
+{
+	return __lse_ll_sc_body(atomic64_dec_if_positive, v);
+}
+
+#define __CMPXCHG_CASE(name, sz)			\
+static inline u##sz __cmpxchg_case_##name##sz(volatile void *ptr,	\
+					      u##sz old,		\
+					      u##sz new)		\
+{									\
+	return __lse_ll_sc_body(_cmpxchg_case_##name##sz,		\
+				ptr, old, new);				\
+}
+
+__CMPXCHG_CASE(    ,  8)
+__CMPXCHG_CASE(    , 16)
+__CMPXCHG_CASE(    , 32)
+__CMPXCHG_CASE(    , 64)
+__CMPXCHG_CASE(acq_,  8)
+__CMPXCHG_CASE(acq_, 16)
+__CMPXCHG_CASE(acq_, 32)
+__CMPXCHG_CASE(acq_, 64)
+__CMPXCHG_CASE(rel_,  8)
+__CMPXCHG_CASE(rel_, 16)
+__CMPXCHG_CASE(rel_, 32)
+__CMPXCHG_CASE(rel_, 64)
+__CMPXCHG_CASE(mb_,  8)
+__CMPXCHG_CASE(mb_, 16)
+__CMPXCHG_CASE(mb_, 32)
+__CMPXCHG_CASE(mb_, 64)
+
+
+#define __CMPXCHG_DBL(name)						\
+static inline long __cmpxchg_double##name(unsigned long old1,		\
+					 unsigned long old2,		\
+					 unsigned long new1,		\
+					 unsigned long new2,		\
+					 volatile void *ptr)		\
+{									\
+	return __lse_ll_sc_body(_cmpxchg_double##name, 			\
+				old1, old2, new1, new2, ptr);		\
+}
+
+__CMPXCHG_DBL(   )
+__CMPXCHG_DBL(_mb)
+
+#endif	/* __ASM_ATOMIC_LSE_H */