arm64: atomics: patch in lse instructions when supported by the CPU

On CPUs which support the LSE atomic instructions introduced in ARMv8.1,
it makes sense to use them in preference to ll/sc sequences.

This patch introduces runtime patching of atomic_t and atomic64_t
routines so that the call-site for the out-of-line ll/sc sequences is
patched with an LSE atomic instruction when we detect that
the CPU supports it.

If binutils is not recent enough to assemble the LSE instructions, then
the ll/sc sequences are inlined as though CONFIG_ARM64_LSE_ATOMICS=n.

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

1 files changed, 34 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/lse.h b/arch/arm64/include/asm/lse.h
new file mode 100644
index 000000000000..d516624a461e
--- /dev/null
+++ b/arch/arm64/include/asm/lse.h
@@ -0,0 +1,34 @@
+#ifndef __ASM_LSE_H
+#define __ASM_LSE_H
+
+#if defined(CONFIG_AS_LSE) && defined(CONFIG_ARM64_LSE_ATOMICS)
+
+#include <linux/stringify.h>
+
+#include <asm/alternative.h>
+#include <asm/cpufeature.h>
+
+__asm__(".arch_extension        lse");
+
+/* Move the ll/sc atomics out-of-line */
+#define __LL_SC_INLINE
+#define __LL_SC_PREFIX(x)       __ll_sc_##x
+#define __LL_SC_EXPORT(x)       EXPORT_SYMBOL(__LL_SC_PREFIX(x))
+
+/* Macro for constructing calls to out-of-line ll/sc atomics */
+#define __LL_SC_CALL(op)        "bl\t" __stringify(__LL_SC_PREFIX(op)) "\n"
+
+/* In-line patching at runtime */
+#define ARM64_LSE_ATOMIC_INSN(llsc, lse)                                \
+        ALTERNATIVE(llsc, lse, ARM64_CPU_FEAT_LSE_ATOMICS)
+
+#else
+
+#define __LL_SC_INLINE          static inline
+#define __LL_SC_PREFIX(x)       x
+#define __LL_SC_EXPORT(x)
+
+#define ARM64_LSE_ATOMIC_INSN(llsc, lse)        llsc
+
+#endif  /* CONFIG_AS_LSE && CONFIG_ARM64_LSE_ATOMICS */
+#endif  /* __ASM_LSE_H */