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	Guo Ren <guoren@linux.alibaba.com>
Subject: [PATCH V11 03/17] riscv: Use Zicbop in arch_xchg when available
Date: Sun, 31 Dec 2023 03:29:54 -0500
Message-Id: <20230910082911.3378782-4-guoren@kernel.org>
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From: Guo Ren <guoren@linux.alibaba.com>

Cache-block prefetch instructions are HINTs to the hardware to
indicate that software intends to perform a particular type of
memory access in the near future. Enable ARCH_HAS_PREFETCHW and
improve the arch_xchg for qspinlock xchg_tail.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/Kconfig                 | 15 +++++++++++++++
 arch/riscv/include/asm/cmpxchg.h   |  4 +++-
 arch/riscv/include/asm/hwcap.h     |  1 +
 arch/riscv/include/asm/insn-def.h  |  5 +++++
 arch/riscv/include/asm/processor.h | 13 +++++++++++++
 arch/riscv/kernel/cpufeature.c     |  1 +
 6 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e9ae6fa232c3..2c346fe169c1 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -617,6 +617,21 @@ config RISCV_ISA_ZICBOZ
 
 	   If you don't know what to do here, say Y.
 
+config RISCV_ISA_ZICBOP
+	bool "Zicbop extension support for cache block prefetch"
+	depends on MMU
+	depends on RISCV_ALTERNATIVE
+	default y
+	help
+	   Adds support to dynamically detect the presence of the ZICBOP
+	   extension (Cache Block Prefetch Operations) and enable its
+	   usage.
+
+	   The Zicbop extension can be used to prefetch cache block for
+	   read/write/instruction fetch.
+
+	   If you don't know what to do here, say Y.
+
 config TOOLCHAIN_HAS_ZIHINTPAUSE
 	bool
 	default y
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 702725727671..56eff7a9d2d2 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -11,6 +11,7 @@
 
 #include <asm/barrier.h>
 #include <asm/fence.h>
+#include <asm/processor.h>
 
 #define __arch_xchg_masked(prepend, append, r, p, n)			\
 ({									\
@@ -25,6 +26,7 @@
 									\
 	__asm__ __volatile__ (						\
 	       prepend							\
+	       PREFETCHW_ASM(%5)					\
 	       "0:	lr.w %0, %2\n"					\
 	       "	and  %1, %0, %z4\n"				\
 	       "	or   %1, %1, %z3\n"				\
@@ -32,7 +34,7 @@
 	       "	bnez %1, 0b\n"					\
 	       append							\
 	       : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b))	\
-	       : "rJ" (__newx), "rJ" (~__mask)				\
+	       : "rJ" (__newx), "rJ" (~__mask), "rJ" (__ptr32b)		\
 	       : "memory");						\
 									\
 	r = (__typeof__(*(p)))((__retx & __mask) >> __s);		\
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index b7b58258f6c7..78b7b8b53778 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -58,6 +58,7 @@
 #define RISCV_ISA_EXT_ZICSR		40
 #define RISCV_ISA_EXT_ZIFENCEI		41
 #define RISCV_ISA_EXT_ZIHPM		42
+#define RISCV_ISA_EXT_ZICBOP		43
 
 #define RISCV_ISA_EXT_MAX		64
 
diff --git a/arch/riscv/include/asm/insn-def.h b/arch/riscv/include/asm/insn-def.h
index 6960beb75f32..dc590d331894 100644
--- a/arch/riscv/include/asm/insn-def.h
+++ b/arch/riscv/include/asm/insn-def.h
@@ -134,6 +134,7 @@
 
 #define RV_OPCODE_MISC_MEM	RV_OPCODE(15)
 #define RV_OPCODE_SYSTEM	RV_OPCODE(115)
+#define RV_OPCODE_PREFETCH	RV_OPCODE(19)
 
 #define HFENCE_VVMA(vaddr, asid)				\
 	INSN_R(OPCODE_SYSTEM, FUNC3(0), FUNC7(17),		\
@@ -196,4 +197,8 @@
 	INSN_I(OPCODE_MISC_MEM, FUNC3(2), __RD(0),		\
 	       RS1(base), SIMM12(4))
 
+#define CBO_prefetchw(base)					\
+	INSN_R(OPCODE_PREFETCH, FUNC3(6), FUNC7(0),		\
+	       RD(x0), RS1(base), RS2(x0))
+
 #endif /* __ASM_INSN_DEF_H */
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index de9da852f78d..7ad3a24212e8 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -12,6 +12,8 @@
 #include <vdso/processor.h>
 
 #include <asm/ptrace.h>
+#include <asm/insn-def.h>
+#include <asm/hwcap.h>
 
 #ifdef CONFIG_64BIT
 #define DEFAULT_MAP_WINDOW	(UL(1) << (MMAP_VA_BITS - 1))
@@ -103,6 +105,17 @@ static inline void arch_thread_struct_whitelist(unsigned long *offset,
 #define KSTK_EIP(tsk)		(ulong)(task_pt_regs(tsk)->epc)
 #define KSTK_ESP(tsk)		(ulong)(task_pt_regs(tsk)->sp)
 
+#define ARCH_HAS_PREFETCHW
+#define PREFETCHW_ASM(base)	ALTERNATIVE(__nops(1), \
+					    CBO_prefetchw(base), \
+					    0, \
+					    RISCV_ISA_EXT_ZICBOP, \
+					    CONFIG_RISCV_ISA_ZICBOP)
+static inline void prefetchw(const void *ptr)
+{
+	asm volatile(PREFETCHW_ASM(%0)
+		: : "r" (ptr) : "memory");
+}
 
 /* Do necessary setup to start up a newly executed thread. */
 extern void start_thread(struct pt_regs *regs,
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index ef7b4fd9e876..e0b897db0b97 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -159,6 +159,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
 	__RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
 	__RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
 	__RISCV_ISA_EXT_DATA(zicboz, RISCV_ISA_EXT_ZICBOZ),
+	__RISCV_ISA_EXT_DATA(zicbop, RISCV_ISA_EXT_ZICBOP),
 	__RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
 	__RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
 	__RISCV_ISA_EXT_DATA(zifencei, RISCV_ISA_EXT_ZIFENCEI),
-- 
2.36.1


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