linux-kernel - [PATCH v4 4/5] riscv: bitops: Use riscv_has_extension

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Message-Id: <20251020-riscv-altn-helper-wip-v4-4-ef941c87669a@iscas.ac.cn>
Date: Mon, 20 Oct 2025 17:09:59 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Yury Norov <yury.norov@...il.com>, 
 Rasmus Villemoes <linux@...musvillemoes.dk>, Paul Walmsley <pjw@...nel.org>
Cc: Charlie Jenkins <charlie@...osinc.com>, 
 Xiao Wang <xiao.w.wang@...el.com>, 
 Christoph Müllner <christoph.muellner@...ll.eu>, 
 Vivian Wang <wangruikang@...as.ac.cn>, Vivian Wang <uwu@...m.page>, 
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v4 4/5] riscv: bitops: Use riscv_has_extension_likely

Use riscv_has_extension_likely() to check for RISCV_ISA_EXT_ZBB,
replacing the use of asm goto with ALTERNATIVE.

The "likely" variant is used to match the behavior of the original
implementation using ALTERNATIVE("j %l[legacy]", "nop", ...).

Signed-off-by: Vivian Wang <wangruikang@...as.ac.cn>
---
 arch/riscv/include/asm/bitops.h | 32 ++++++++------------------------
 1 file changed, 8 insertions(+), 24 deletions(-)

diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
index 77880677b06e..238092125c11 100644
--- a/arch/riscv/include/asm/bitops.h
+++ b/arch/riscv/include/asm/bitops.h
@@ -47,9 +47,8 @@
 
 static __always_inline __attribute_const__ unsigned long variable__ffs(unsigned long word)
 {
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (!riscv_has_extension_likely(RISCV_ISA_EXT_ZBB))
+		return generic___ffs(word);
 
 	asm volatile (".option push\n"
 		      ".option arch,+zbb\n"
@@ -58,9 +57,6 @@ static __always_inline __attribute_const__ unsigned long variable__ffs(unsigned
 		      : "=r" (word) : "r" (word) :);
 
 	return word;
-
-legacy:
-	return generic___ffs(word);
 }
 
 /**
@@ -76,9 +72,8 @@ static __always_inline __attribute_const__ unsigned long variable__ffs(unsigned
 
 static __always_inline __attribute_const__ unsigned long variable__fls(unsigned long word)
 {
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (!riscv_has_extension_likely(RISCV_ISA_EXT_ZBB))
+		return generic___fls(word);
 
 	asm volatile (".option push\n"
 		      ".option arch,+zbb\n"
@@ -87,9 +82,6 @@ static __always_inline __attribute_const__ unsigned long variable__fls(unsigned
 		      : "=r" (word) : "r" (word) :);
 
 	return BITS_PER_LONG - 1 - word;
-
-legacy:
-	return generic___fls(word);
 }
 
 /**
@@ -105,9 +97,8 @@ static __always_inline __attribute_const__ unsigned long variable__fls(unsigned
 
 static __always_inline __attribute_const__ int variable_ffs(int x)
 {
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (!riscv_has_extension_likely(RISCV_ISA_EXT_ZBB))
+		return generic_ffs(x);
 
 	if (!x)
 		return 0;
@@ -119,9 +110,6 @@ static __always_inline __attribute_const__ int variable_ffs(int x)
 		      : "=r" (x) : "r" (x) :);
 
 	return x + 1;
-
-legacy:
-	return generic_ffs(x);
 }
 
 /**
@@ -137,9 +125,8 @@ static __always_inline __attribute_const__ int variable_ffs(int x)
 
 static __always_inline int variable_fls(unsigned int x)
 {
-	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,
-				      RISCV_ISA_EXT_ZBB, 1)
-			  : : : : legacy);
+	if (!riscv_has_extension_likely(RISCV_ISA_EXT_ZBB))
+		return generic_fls(x);
 
 	if (!x)
 		return 0;
@@ -151,9 +138,6 @@ static __always_inline int variable_fls(unsigned int x)
 		      : "=r" (x) : "r" (x) :);
 
 	return 32 - x;
-
-legacy:
-	return generic_fls(x);
 }
 
 /**

-- 
2.51.0