linux-kernel - [PATCH v13 2/5] riscv: Add static key for misaligned accesses

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Message-Id: <20231220-optimize_checksum-v13-2-a73547e1cad8@rivosinc.com>
Date: Wed, 20 Dec 2023 15:37:40 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Charlie Jenkins <charlie@...osinc.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Conor Dooley <conor@...nel.org>, 
 Samuel Holland <samuel.holland@...ive.com>, 
 David Laight <David.Laight@...lab.com>, Xiao Wang <xiao.w.wang@...el.com>, 
 Evan Green <evan@...osinc.com>, linux-riscv@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Cc: Paul Walmsley <paul.walmsley@...ive.com>, 
 Albert Ou <aou@...s.berkeley.edu>, Arnd Bergmann <arnd@...db.de>
Subject: [PATCH v13 2/5] riscv: Add static key for misaligned accesses

Support static branches depending on the value of misaligned accesses.
This will be used by a later patch in the series. All cpus must be
considered "fast" for this static branch to be flipped.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
 arch/riscv/include/asm/cpufeature.h |  2 ++
 arch/riscv/kernel/cpufeature.c      | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index a418c3112cd6..7b129e5e2f07 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -133,4 +133,6 @@ static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsi
 	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
 }
 
+DECLARE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
+
 #endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index b3785ffc1570..095eb6ebdcaa 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -10,6 +10,7 @@
 #include <linux/bitmap.h>
 #include <linux/cpuhotplug.h>
 #include <linux/ctype.h>
+#include <linux/jump_label.h>
 #include <linux/log2.h>
 #include <linux/memory.h>
 #include <linux/module.h>
@@ -728,6 +729,35 @@ void riscv_user_isa_enable(void)
 		csr_set(CSR_SENVCFG, ENVCFG_CBZE);
 }
 
+DEFINE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
+
+static int set_unaligned_access_static_branches(void)
+{
+	/*
+	 * This will be called after check_unaligned_access_all_cpus so the
+	 * result of unaligned access speed for all cpus will be available.
+	 */
+
+	int cpu;
+	bool fast_misaligned_access_speed = true;
+
+	for_each_online_cpu(cpu) {
+		int this_perf = per_cpu(misaligned_access_speed, cpu);
+
+		if (this_perf != RISCV_HWPROBE_MISALIGNED_FAST) {
+			fast_misaligned_access_speed = false;
+			break;
+		}
+	}
+
+	if (fast_misaligned_access_speed)
+		static_branch_enable(&fast_misaligned_access_speed_key);
+
+	return 0;
+}
+
+arch_initcall_sync(set_unaligned_access_static_branches);
+
 #ifdef CONFIG_RISCV_ALTERNATIVE
 /*
  * Alternative patch sites consider 48 bits when determining when to patch

-- 
2.43.0