riscv: Improve zacas fully-ordered cmpxchg()

The current fully-ordered cmpxchgXX() implementation results in:

  amocas.X.rl     a5,a4,(s1)
  fence           rw,rw

This provides enough sync but we can actually use the following better
mapping instead:

  amocas.X.aqrl   a5,a4,(s1)

Suggested-by: Andrea Parri <andrea@rivosinc.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Andrea Parri <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20241103145153.105097-7-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/cmpxchg.h

@@ -107,8 +107,10 @@
  * store NEW in MEM.  Return the initial value in MEM.  Success is
  * indicated by comparing RETURN with OLD.
  */
-
-#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, prepend, append, r, p, o, n)	\
+#define __arch_cmpxchg_masked(sc_sfx, cas_sfx,					\
+			      sc_prepend, sc_append,				\
+			      cas_prepend, cas_append,				\
+			      r, p, o, n)					\
 ({										\
 	if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) &&				\
 	    IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) &&				\
@@ -117,9 +119,9 @@
 		r = o;								\
 										\
 		__asm__ __volatile__ (						\
-			prepend							\
+			cas_prepend							\
 			"	amocas" cas_sfx " %0, %z2, %1\n"		\
-			append							\
+			cas_append							\
 			: "+&r" (r), "+A" (*(p))				\
 			: "rJ" (n)						\
 			: "memory");						\
@@ -134,15 +136,15 @@
 		ulong __rc;							\
 										\
 		__asm__ __volatile__ (						\
-			prepend							\
+			sc_prepend							\
 			"0:	lr.w %0, %2\n"					\
 			"	and  %1, %0, %z5\n"				\
 			"	bne  %1, %z3, 1f\n"				\
 			"	and  %1, %0, %z6\n"				\
 			"	or   %1, %1, %z4\n"				\
 			"	sc.w" sc_sfx " %1, %1, %2\n"			\
 			"	bnez %1, 0b\n"					\
-			append							\
+			sc_append							\
 			"1:\n"							\
 			: "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b))	\
 			: "rJ" ((long)__oldx), "rJ" (__newx),			\
@@ -153,37 +155,42 @@
 	}									\
 })
 
-#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n)	\
+#define __arch_cmpxchg(lr_sfx, sc_sfx, cas_sfx,				\
+		       sc_prepend, sc_append,				\
+		       cas_prepend, cas_append,				\
+		       r, p, co, o, n)					\
 ({									\
 	if (IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) &&			\
 	    riscv_has_extension_unlikely(RISCV_ISA_EXT_ZACAS)) {	\
 		r = o;							\
 									\
 		__asm__ __volatile__ (					\
-			prepend						\
-			"	amocas" sc_cas_sfx " %0, %z2, %1\n"	\
-			append						\
+			cas_prepend					\
+			"	amocas" cas_sfx " %0, %z2, %1\n"	\
+			cas_append					\
 			: "+&r" (r), "+A" (*(p))			\
 			: "rJ" (n)					\
 			: "memory");					\
 	} else {							\
 		register unsigned int __rc;				\
 									\
 		__asm__ __volatile__ (					\
-			prepend						\
+			sc_prepend					\
 			"0:	lr" lr_sfx " %0, %2\n"			\
 			"	bne  %0, %z3, 1f\n"			\
-			"	sc" sc_cas_sfx " %1, %z4, %2\n"		\
+			"	sc" sc_sfx " %1, %z4, %2\n"		\
 			"	bnez %1, 0b\n"				\
-			append						\
+			sc_append					\
 			"1:\n"						\
 			: "=&r" (r), "=&r" (__rc), "+A" (*(p))		\
 			: "rJ" (co o), "rJ" (n)				\
 			: "memory");					\
 	}								\
 })
 
-#define _arch_cmpxchg(ptr, old, new, sc_cas_sfx, prepend, append)	\
+#define _arch_cmpxchg(ptr, old, new, sc_sfx, cas_sfx,			\
+		      sc_prepend, sc_append,				\
+		      cas_prepend, cas_append)				\
 ({									\
 	__typeof__(ptr) __ptr = (ptr);					\
 	__typeof__(*(__ptr)) __old = (old);				\
@@ -192,40 +199,69 @@
 									\
 	switch (sizeof(*__ptr)) {					\
 	case 1:								\
-		__arch_cmpxchg_masked(sc_cas_sfx, ".b" sc_cas_sfx,	\
-					prepend, append,		\
-					__ret, __ptr, __old, __new);    \
+		__arch_cmpxchg_masked(sc_sfx, ".b" cas_sfx,		\
+				      sc_prepend, sc_append,		\
+				      cas_prepend, cas_append,		\
+				      __ret, __ptr, __old, __new);	\
 		break;							\
 	case 2:								\
-		__arch_cmpxchg_masked(sc_cas_sfx, ".h" sc_cas_sfx,	\
-					prepend, append,		\
-					__ret, __ptr, __old, __new);	\
+		__arch_cmpxchg_masked(sc_sfx, ".h" cas_sfx,		\
+				      sc_prepend, sc_append,		\
+				      cas_prepend, cas_append,		\
+				      __ret, __ptr, __old, __new);	\
 		break;							\
 	case 4:								\
-		__arch_cmpxchg(".w", ".w" sc_cas_sfx, prepend, append,	\
-				__ret, __ptr, (long), __old, __new);	\
+		__arch_cmpxchg(".w", ".w" sc_sfx, ".w" cas_sfx,		\
+			       sc_prepend, sc_append,			\
+			       cas_prepend, cas_append,			\
+			       __ret, __ptr, (long), __old, __new);	\
 		break;							\
 	case 8:								\
-		__arch_cmpxchg(".d", ".d" sc_cas_sfx, prepend, append,	\
-				__ret, __ptr, /**/, __old, __new);	\
+		__arch_cmpxchg(".d", ".d" sc_sfx, ".d" cas_sfx,		\
+			       sc_prepend, sc_append,			\
+			       cas_prepend, cas_append,			\
+			       __ret, __ptr, /**/, __old, __new);	\
 		break;							\
 	default:							\
 		BUILD_BUG();						\
 	}								\
 	(__typeof__(*(__ptr)))__ret;					\
 })
 
+/*
+ * These macros are here to improve the readability of the arch_cmpxchg_XXX()
+ * macros.
+ */
+#define SC_SFX(x)	x
+#define CAS_SFX(x)	x
+#define SC_PREPEND(x)	x
+#define SC_APPEND(x)	x
+#define CAS_PREPEND(x)	x
+#define CAS_APPEND(x)	x
+
 #define arch_cmpxchg_relaxed(ptr, o, n)					\
-	_arch_cmpxchg((ptr), (o), (n), "", "", "")
+	_arch_cmpxchg((ptr), (o), (n),					\
+		      SC_SFX(""), CAS_SFX(""),				\
+		      SC_PREPEND(""), SC_APPEND(""),			\
+		      CAS_PREPEND(""), CAS_APPEND(""))
 
 #define arch_cmpxchg_acquire(ptr, o, n)					\
-	_arch_cmpxchg((ptr), (o), (n), "", "", RISCV_ACQUIRE_BARRIER)
+	_arch_cmpxchg((ptr), (o), (n),					\
+		      SC_SFX(""), CAS_SFX(""),				\
+		      SC_PREPEND(""), SC_APPEND(RISCV_ACQUIRE_BARRIER),	\
+		      CAS_PREPEND(""), CAS_APPEND(RISCV_ACQUIRE_BARRIER))
 
 #define arch_cmpxchg_release(ptr, o, n)					\
-	_arch_cmpxchg((ptr), (o), (n), "", RISCV_RELEASE_BARRIER, "")
+	_arch_cmpxchg((ptr), (o), (n),					\
+		      SC_SFX(""), CAS_SFX(""),				\
+		      SC_PREPEND(RISCV_RELEASE_BARRIER), SC_APPEND(""),	\
+		      CAS_PREPEND(RISCV_RELEASE_BARRIER), CAS_APPEND(""))
 
 #define arch_cmpxchg(ptr, o, n)						\
-	_arch_cmpxchg((ptr), (o), (n), ".rl", "", "	fence rw, rw\n")
+	_arch_cmpxchg((ptr), (o), (n),					\
+		      SC_SFX(".rl"), CAS_SFX(".aqrl"),			\
+		      SC_PREPEND(""), SC_APPEND(RISCV_FULL_BARRIER),	\
+		      CAS_PREPEND(""), CAS_APPEND(""))
 
 #define arch_cmpxchg_local(ptr, o, n)					\
 	arch_cmpxchg_relaxed((ptr), (o), (n))