linux-kernel - [PATCH v10 2/5] riscv: Add static key for misaligned accesses

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Message-Id: <20231101-optimize_checksum-v10-2-a498577bb969@rivosinc.com>
Date:   Wed, 01 Nov 2023 15:48:12 -0700
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 v10 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 |  3 +++
 arch/riscv/kernel/cpufeature.c      | 30 ++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index b139796392d0..febd9de4373e 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -7,6 +7,7 @@
 #define _ASM_CPUFEATURE_H
 
 #include <linux/bitmap.h>
+#include <linux/jump_label.h>
 #include <asm/hwcap.h>
 
 /*
@@ -32,4 +33,6 @@ extern struct riscv_isainfo hart_isa[NR_CPUS];
 
 int check_unaligned_access(void *unused);
 
+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 40bb854fcb96..8935481d32da 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -9,6 +9,7 @@
 #include <linux/acpi.h>
 #include <linux/bitmap.h>
 #include <linux/ctype.h>
+#include <linux/jump_label.h>
 #include <linux/log2.h>
 #include <linux/memory.h>
 #include <linux/module.h>
@@ -665,6 +666,35 @@ static int check_unaligned_access_all_cpus(void)
 
 arch_initcall(check_unaligned_access_all_cpus);
 
+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

-- 
2.34.1