linux-kernel - [PATCH v2 2/2] LoongArch: Detect PMU bits via CPUCFG instruction

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Message-ID: <20251110025906.17096-3-yangtiezhu@loongson.cn>
Date: Mon, 10 Nov 2025 10:59:06 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] LoongArch: Detect PMU bits via CPUCFG instruction

Detect the value of PMU bits via CPUCFG instruction according to
the ISA manual instead of hard-coded as 64, because the value may
be different for various micro-architectures.

Link: https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#_cpucfg
Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 arch/loongarch/include/asm/loongarch.h | 1 +
 arch/loongarch/kernel/perf_event.c     | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/loongarch/include/asm/loongarch.h b/arch/loongarch/include/asm/loongarch.h
index 09dfd7eb406e..89343b1a526f 100644
--- a/arch/loongarch/include/asm/loongarch.h
+++ b/arch/loongarch/include/asm/loongarch.h
@@ -128,6 +128,7 @@
 #define  CPUCFG6_PMNUM			GENMASK(7, 4)
 #define  CPUCFG6_PMNUM_SHIFT		4
 #define  CPUCFG6_PMBITS			GENMASK(13, 8)
+#define  CPUCFG6_PMBITS_SHIFT		8
 #define  CPUCFG6_UPM			BIT(14)
 
 #define LOONGARCH_CPUCFG16		0x10
diff --git a/arch/loongarch/kernel/perf_event.c b/arch/loongarch/kernel/perf_event.c
index 2d0c14bdadda..9d257c8519c9 100644
--- a/arch/loongarch/kernel/perf_event.c
+++ b/arch/loongarch/kernel/perf_event.c
@@ -845,12 +845,13 @@ static const struct loongarch_perf_event *loongarch_pmu_map_raw_event(u64 config
 
 static int __init init_hw_perf_events(void)
 {
-	int counters;
+	int bits, counters;
 
 	if (!cpu_has_pmp)
 		return -ENODEV;
 
 	pr_info("Performance counters: ");
+	bits = ((read_cpucfg(LOONGARCH_CPUCFG6) & CPUCFG6_PMBITS) >> CPUCFG6_PMBITS_SHIFT) + 1;
 	counters = ((read_cpucfg(LOONGARCH_CPUCFG6) & CPUCFG6_PMNUM) >> CPUCFG6_PMNUM_SHIFT) + 1;
 
 	loongarch_pmu.num_counters = counters;
@@ -867,7 +868,7 @@ static int __init init_hw_perf_events(void)
 	on_each_cpu(reset_counters, NULL, 1);
 
 	pr_cont("%s PMU enabled, %d %d-bit counters available to each CPU.\n",
-			loongarch_pmu.name, counters, 64);
+			loongarch_pmu.name, counters, bits);
 
 	perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
 
-- 
2.42.0