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>

arch/arm64/Makefile

@@ -17,7 +17,18 @@ GZFLAGS		:=-9
 
 KBUILD_DEFCONFIG := defconfig
 
-KBUILD_CFLAGS	+= -mgeneral-regs-only
+# Check for binutils support for specific extensions
+lseinstr := $(call as-instr,.arch_extension lse,-DCONFIG_AS_LSE=1)
+
+ifeq ($(CONFIG_ARM64_LSE_ATOMICS), y)
+  ifeq ($(lseinstr),)
+$(warning LSE atomics not supported by binutils)
+  endif
+endif
+
+KBUILD_CFLAGS	+= -mgeneral-regs-only $(lseinstr)
+KBUILD_AFLAGS	+= $(lseinstr)
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 AS		+= -EB

arch/arm64/include/asm/atomic.h

@@ -21,19 +21,19 @@
 #define __ASM_ATOMIC_H
 
 #include <linux/compiler.h>
-#include <linux/stringify.h>
 #include <linux/types.h>
 
 #include <asm/barrier.h>
 #include <asm/cmpxchg.h>
+#include <asm/lse.h>
 
 #define ATOMIC_INIT(i)	{ (i) }
 
 #ifdef __KERNEL__
 
 #define __ARM64_IN_ATOMIC_IMPL
 
-#ifdef CONFIG_ARM64_LSE_ATOMICS
+#if defined(CONFIG_ARM64_LSE_ATOMICS) && defined(CONFIG_AS_LSE)
 #include <asm/atomic_lse.h>
 #else
 #include <asm/atomic_ll_sc.h>

arch/arm64/include/asm/atomic_ll_sc.h

@@ -37,18 +37,6 @@
  * (the optimize attribute silently ignores these options).
  */
 
-#ifndef __LL_SC_INLINE
-#define __LL_SC_INLINE		static inline
-#endif
-
-#ifndef __LL_SC_PREFIX
-#define __LL_SC_PREFIX(x)	x
-#endif
-
-#ifndef __LL_SC_EXPORT
-#define __LL_SC_EXPORT(x)
-#endif
-
 #define ATOMIC_OP(op, asm_op)						\
 __LL_SC_INLINE void							\
 __LL_SC_PREFIX(atomic_##op(int i, atomic_t *v))				\