linux-kernel - [PATCH V2 2/2] csky: atomic: Add custom atomic.h implementation

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Message-Id: <20220411145146.920314-3-guoren@kernel.org>
Date:   Mon, 11 Apr 2022 22:51:46 +0800
From:   guoren@...nel.org
To:     guoren@...nel.org, arnd@...db.de, mark.rutland@....com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-csky@...r.kernel.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH V2 2/2] csky: atomic: Add custom atomic.h implementation

From: Guo Ren <guoren@...ux.alibaba.com>

The generic atomic.h used cmpxchg to implement the atomic
operations, it will cause daul loop to reduce the forward
guarantee. The patch implement csky custom atomic operations with
ldex/stex instructions for the best performance.

Important reference comment by Rutland:
8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for
full barrier semantics")

Link: https://lore.kernel.org/linux-riscv/CAJF2gTSAxpAi=LbAdu7jntZRUa=-dJwL0VfmDfBV5MHB=rcZ-w@mail.gmail.com/T/#m27a0f1342995deae49ce1d0e1f2683f8a181d6c3
Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>
---
Changes in V2:
 - Fixup use of acquire + release for barrier semantics by Rutland.
---
 arch/csky/include/asm/atomic.h | 130 +++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 arch/csky/include/asm/atomic.h

diff --git a/arch/csky/include/asm/atomic.h b/arch/csky/include/asm/atomic.h
new file mode 100644
index 000000000000..2e1a22f55ea1
--- /dev/null
+++ b/arch/csky/include/asm/atomic.h
@@ -0,0 +1,130 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __ASM_CSKY_ATOMIC_H
+#define __ASM_CSKY_ATOMIC_H
+
+#ifdef CONFIG_SMP
+# include <asm-generic/atomic64.h>
+
+#include <asm/cmpxchg.h>
+#include <asm/barrier.h>
+
+#define __atomic_acquire_fence()	__smp_acquire_fence()
+
+#define __atomic_release_fence()	__smp_release_fence()
+
+static __always_inline int arch_atomic_read(const atomic_t *v)
+{
+	return READ_ONCE(v->counter);
+}
+static __always_inline void arch_atomic_set(atomic_t *v, int i)
+{
+	WRITE_ONCE(v->counter, i);
+}
+
+#define ATOMIC_OP(op, asm_op, I)					\
+static __always_inline							\
+void arch_atomic_##op(int i, atomic_t *v)				\
+{									\
+	unsigned long tmp;						\
+	__asm__ __volatile__ (						\
+	"1:	ldex.w		%0, (%2)	\n"			\
+	"	" #op "		%0, %1		\n"			\
+	"	stex.w		%0, (%2)	\n"			\
+	"	bez		%0, 1b		\n"			\
+	: "=&r" (tmp)							\
+	: "r" (I), "r" (&v->counter)					\
+	: "memory");							\
+}
+
+ATOMIC_OP(add, add,  i)
+ATOMIC_OP(sub, add, -i)
+ATOMIC_OP(and, and,  i)
+ATOMIC_OP( or,  or,  i)
+ATOMIC_OP(xor, xor,  i)
+
+#undef ATOMIC_OP
+
+#define ATOMIC_FETCH_OP(op, asm_op, I)					\
+static __always_inline							\
+int arch_atomic_fetch_##op##_relaxed(int i, atomic_t *v)		\
+{									\
+	register int ret, tmp;						\
+	__asm__ __volatile__ (						\
+	"1:	ldex.w		%0, (%3) \n"				\
+	"	mov		%1, %0   \n"				\
+	"	" #op "		%0, %2   \n"				\
+	"	stex.w		%0, (%3) \n"				\
+	"	bez		%0, 1b   \n"				\
+		: "=&r" (tmp), "=&r" (ret)				\
+		: "r" (I), "r"(&v->counter) 				\
+		: "memory");						\
+	return ret;							\
+}
+
+#define ATOMIC_OP_RETURN(op, asm_op, c_op, I)				\
+static __always_inline							\
+int arch_atomic_##op##_return_relaxed(int i, atomic_t *v)		\
+{									\
+        return arch_atomic_fetch_##op##_relaxed(i, v) c_op I;		\
+}
+
+#define ATOMIC_OPS(op, asm_op, c_op, I)					\
+        ATOMIC_FETCH_OP( op, asm_op,       I)				\
+        ATOMIC_OP_RETURN(op, asm_op, c_op, I)
+
+ATOMIC_OPS(add, add, +,  i)
+ATOMIC_OPS(sub, add, +, -i)
+
+#define arch_atomic_fetch_add_relaxed	arch_atomic_fetch_add_relaxed
+#define arch_atomic_fetch_sub_relaxed	arch_atomic_fetch_sub_relaxed
+
+#define arch_atomic_add_return_relaxed	arch_atomic_add_return_relaxed
+#define arch_atomic_sub_return_relaxed	arch_atomic_sub_return_relaxed
+
+#undef ATOMIC_OPS
+#undef ATOMIC_OP_RETURN
+
+#define ATOMIC_OPS(op, asm_op, I)					\
+        ATOMIC_FETCH_OP(op, asm_op, I)
+
+ATOMIC_OPS(and, and, i)
+ATOMIC_OPS( or,  or, i)
+ATOMIC_OPS(xor, xor, i)
+
+#define arch_atomic_fetch_and_relaxed	arch_atomic_fetch_and_relaxed
+#define arch_atomic_fetch_or_relaxed	arch_atomic_fetch_or_relaxed
+#define arch_atomic_fetch_xor_relaxed	arch_atomic_fetch_xor_relaxed
+
+#undef ATOMIC_OPS
+
+#undef ATOMIC_FETCH_OP
+
+#define ATOMIC_OP()							\
+static __always_inline							\
+int arch_atomic_xchg_relaxed(atomic_t *v, int n)			\
+{									\
+	return __xchg_relaxed(n, &(v->counter), 4);			\
+}									\
+static __always_inline							\
+int arch_atomic_cmpxchg_relaxed(atomic_t *v, int o, int n)		\
+{									\
+	return __cmpxchg_relaxed(&(v->counter), o, n, 4);		\
+}
+
+#define ATOMIC_OPS()							\
+	ATOMIC_OP()
+
+ATOMIC_OPS()
+
+#define arch_atomic_xchg_relaxed	arch_atomic_xchg_relaxed
+#define arch_atomic_cmpxchg_relaxed	arch_atomic_cmpxchg_relaxed
+
+#undef ATOMIC_OPS
+#undef ATOMIC_OP
+
+#else
+# include <asm-generic/atomic.h>
+#endif
+
+#endif /* __ASM_CSKY_ATOMIC_H */
-- 
2.25.1