linux-kernel - [PATCH RFC cmpxchg 8/8] riscv: Emulate one-byte and two-byte cmpxchg

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Message-Id: <20240401213950.3910531-8-paulmck@kernel.org>
Date: Mon,  1 Apr 2024 14:39:50 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: kernel-team@...a.com,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Andi Shyti <andi.shyti@...ux.intel.com>,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	linux-riscv@...ts.infradead.org
Subject: [PATCH RFC cmpxchg 8/8] riscv: Emulate one-byte and two-byte cmpxchg

Use the new cmpxchg_emu_u8() and cmpxchg_emu_u16() to emulate one-byte
and two-byte cmpxchg() on riscv.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Andi Shyti <andi.shyti@...ux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>
Cc: <linux-riscv@...ts.infradead.org>
---
 arch/riscv/Kconfig               |  1 +
 arch/riscv/include/asm/cmpxchg.h | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index be09c8836d56b..4eaf40d0a52ec 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -44,6 +44,7 @@ config RISCV
 	select ARCH_HAS_UBSAN
 	select ARCH_HAS_VDSO_DATA
 	select ARCH_KEEP_MEMBLOCK if ACPI
+	select ARCH_NEED_CMPXCHG_1_2_EMU
 	select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
 	select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
 	select ARCH_STACKWALK
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 2fee65cc84432..a5b377481785c 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -9,6 +9,7 @@
 #include <linux/bug.h>
 
 #include <asm/fence.h>
+#include <linux/cmpxchg-emu.h>
 
 #define __xchg_relaxed(ptr, new, size)					\
 ({									\
@@ -170,6 +171,12 @@
 	__typeof__(*(ptr)) __ret;					\
 	register unsigned int __rc;					\
 	switch (size) {							\
+	case 1:								\
+		__ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+		break;							\
+	case 2:								\
+		break;							\
+		__ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
 	case 4:								\
 		__asm__ __volatile__ (					\
 			"0:	lr.w %0, %2\n"				\
@@ -214,6 +221,12 @@
 	__typeof__(*(ptr)) __ret;					\
 	register unsigned int __rc;					\
 	switch (size) {							\
+	case 1:								\
+		__ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+		break;							\
+	case 2:								\
+		break;							\
+		__ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
 	case 4:								\
 		__asm__ __volatile__ (					\
 			"0:	lr.w %0, %2\n"				\
@@ -260,6 +273,12 @@
 	__typeof__(*(ptr)) __ret;					\
 	register unsigned int __rc;					\
 	switch (size) {							\
+	case 1:								\
+		__ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+		break;							\
+	case 2:								\
+		break;							\
+		__ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
 	case 4:								\
 		__asm__ __volatile__ (					\
 			RISCV_RELEASE_BARRIER				\
@@ -306,6 +325,12 @@
 	__typeof__(*(ptr)) __ret;					\
 	register unsigned int __rc;					\
 	switch (size) {							\
+	case 1:								\
+		__ret = cmpxchg_emu_u8((volatile u8 *)__ptr, __old, __new); \
+		break;							\
+	case 2:								\
+		break;							\
+		__ret = cmpxchg_emu_u16((volatile u16 *)__ptr, __old, __new); \
 	case 4:								\
 		__asm__ __volatile__ (					\
 			"0:	lr.w %0, %2\n"				\
-- 
2.40.1