riscv: checksum: 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[no_zbb]", "nop", ...).

While we're at it, also remove bogus comment about Zbb being likely
available. We have to choose between "likely" and "unlikely" due to
limitations of the asm goto feature, but that does not mean we should
put a bad comment on why we pick "likely" over "unlikely".

Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
Link: https://patch.msgid.link/20251020-riscv-altn-helper-wip-v4-2-ef941c87669a@iscas.ac.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>

1 files changed, 12 insertions, 41 deletions

diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c
index 9408f50ca59a..75bd0abffd63 100644
--- a/arch/riscv/lib/csum.c
+++ b/arch/riscv/lib/csum.c
@@ -40,20 +40,11 @@ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 	uproto = (__force unsigned int)htonl(proto);
 	sum += uproto;
 
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
+	    IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB) &&
+	    riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {
 		unsigned long fold_temp;
 
-		/*
-		 * Zbb is likely available when the kernel is compiled with Zbb
-		 * support, so nop when Zbb is available and jump when Zbb is
-		 * not available.
-		 */
-		asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
-					      RISCV_ISA_EXT_ZBB, 1)
-				  :
-				  :
-				  :
-				  : no_zbb);
 		asm(".option push					\n\
 		.option arch,+zbb					\n\
 			rori	%[fold_temp], %[sum], 32		\n\
@@ -66,7 +57,7 @@ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
 		: [sum] "+r" (sum), [fold_temp] "=&r" (fold_temp));
 		return (__force __sum16)(sum >> 16);
 	}
-no_zbb:
+
 	sum += ror64(sum, 32);
 	sum >>= 32;
 	return csum_fold((__force __wsum)sum);
@@ -152,21 +143,11 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 	csum = do_csum_common(ptr, end, data);
 
 #ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
+	    IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB) &&
+	    riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {
 		unsigned long fold_temp;
 
-		/*
-		 * Zbb is likely available when the kernel is compiled with Zbb
-		 * support, so nop when Zbb is available and jump when Zbb is
-		 * not available.
-		 */
-		asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
-					      RISCV_ISA_EXT_ZBB, 1)
-				  :
-				  :
-				  :
-				  : no_zbb);
-
 #ifdef CONFIG_32BIT
 		asm_goto_output(".option push			\n\
 		.option arch,+zbb				\n\
@@ -204,7 +185,7 @@ do_csum_with_alignment(const unsigned char *buff, int len)
 end:
 		return csum >> 16;
 	}
-no_zbb:
+
 #endif /* CC_HAS_ASM_GOTO_TIED_OUTPUT */
 #ifndef CONFIG_32BIT
 	csum += ror64(csum, 32);
@@ -234,21 +215,11 @@ do_csum_no_alignment(const unsigned char *buff, int len)
 	end = (const unsigned long *)(buff + len);
 	csum = do_csum_common(ptr, end, data);
 
-	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) {
+	if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) &&
+	    IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB) &&
+	    riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {
 		unsigned long fold_temp;
 
-		/*
-		 * Zbb is likely available when the kernel is compiled with Zbb
-		 * support, so nop when Zbb is available and jump when Zbb is
-		 * not available.
-		 */
-		asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0,
-					      RISCV_ISA_EXT_ZBB, 1)
-				  :
-				  :
-				  :
-				  : no_zbb);
-
 #ifdef CONFIG_32BIT
 		asm (".option push				\n\
 		.option arch,+zbb				\n\
@@ -274,7 +245,7 @@ do_csum_no_alignment(const unsigned char *buff, int len)
 #endif /* !CONFIG_32BIT */
 		return csum >> 16;
 	}
-no_zbb:
+
 #ifndef CONFIG_32BIT
 	csum += ror64(csum, 32);
 	csum >>= 32;