[PATCH 3/4] RISC-V: add cpufeature probing for fast-unaligned access

[Heiko Stuebner]

From: Heiko Stuebner <heiko.stuebner at vrull.eu>

Use the recently added misaligned access descriptor and derive a cpufeature
id from it so that it can be used in alternative patches.

We assume slow unaligned access if any cpu-core does not support fast
access.

Signed-off-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
---
 arch/riscv/include/asm/errata_list.h |  9 +++++----
 arch/riscv/kernel/cpufeature.c       | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
index 043b79c79824..6ce0c22ae994 100644
--- a/arch/riscv/include/asm/errata_list.h
+++ b/arch/riscv/include/asm/errata_list.h
@@ -22,10 +22,11 @@
 #define	ERRATA_THEAD_NUMBER 3
 #endif
 
-#define	CPUFEATURE_SVPBMT 	(1 << 0)
-#define	CPUFEATURE_ZICBOM	(1 << 1)
-#define	CPUFEATURE_ZBB		(1 << 2)
-#define	CPUFEATURE_NUMBER 3
+#define	CPUFEATURE_SVPBMT 		(1 << 0)
+#define	CPUFEATURE_ZICBOM		(1 << 1)
+#define	CPUFEATURE_ZBB			(1 << 2)
+#define	CPUFEATURE_FAST_UNALIGNED	(1 << 3)
+#define	CPUFEATURE_NUMBER		4
 
 #ifdef __ASSEMBLY__
 
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index a65bebdadb68..640b78f6aaa9 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -337,6 +337,23 @@ static bool __init_or_module cpufeature_probe_zbb(unsigned int stage)
 	return true;
 }
 
+static bool __init_or_module cpufeature_probe_fast_unaligned(unsigned int stage)
+{
+	int cpu;
+
+	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+		return false;
+
+	for_each_possible_cpu(cpu) {
+		long perf = per_cpu(misaligned_access_speed, cpu);
+
+		if (perf != RISCV_HWPROBE_MISALIGNED_FAST)
+			return false;
+	}
+
+	return true;
+}
+
 /*
  * Probe presence of individual extensions.
  *
@@ -358,6 +375,9 @@ static u32 __init_or_module cpufeature_probe(unsigned int stage)
 	if (cpufeature_probe_zbb(stage))
 		cpu_req_feature |= CPUFEATURE_ZBB;
 
+	if (cpufeature_probe_fast_unaligned(stage))
+		cpu_req_feature |= CPUFEATURE_FAST_UNALIGNED;
+
 	return cpu_req_feature;
 }
 
-- 
2.35.1