[PATCH v3 5/7] perf: arm_pmuv3: Add pmuv3_event_implemented()

[Amir Ayupov]

Drivers outside the PMU driver may need to know whether the local CPU's
PMU implements a common event before relying on it, for example a trace
unit driver checking that the PMU counts its external outputs as
TRCEXTOUTn.

Add pmuv3_event_implemented(), which reads PMCEID0/1 on the calling CPU:
events 0x0000-0x003f are reported in bits [31:0], and the common events
from ARMV8_PMUV3_EXT_COMMON_EVENT_BASE in bits [63:32] from PMUv3p1. Move
ARMV8_PMUV3_EXT_COMMON_EVENT_BASE next to the event numbers in
arm_pmuv3.h so it is available without CONFIG_ARM_PMU.

Suggested-by: James Clark <james.clark@xxxxxxxxxx>
Assisted-by: Devmate:Opus-5.5
Signed-off-by: Amir Ayupov <aaupov@xxxxxx>
---
 include/linux/perf/arm_pmu.h   |  1 -
 include/linux/perf/arm_pmuv3.h | 22 ++++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
index 02d2c7f45b527..792283d29d7b5 100644
--- a/include/linux/perf/arm_pmu.h
+++ b/include/linux/perf/arm_pmu.h
@@ -124,7 +124,6 @@ struct arm_pmu {
 	u64		reg_brbidr;
 #define ARMV8_PMUV3_MAX_COMMON_EVENTS		0x40
 	DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
-#define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE	0x4000
 	DECLARE_BITMAP(pmceid_ext_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
 
 	/* Only to be used by ACPI probing code */
diff --git a/include/linux/perf/arm_pmuv3.h b/include/linux/perf/arm_pmuv3.h
index d698efba28a27..965c40b28dd77 100644
--- a/include/linux/perf/arm_pmuv3.h
+++ b/include/linux/perf/arm_pmuv3.h
@@ -78,6 +78,9 @@
 #define ARMV8_PMUV3_PERFCTR_STALL_SLOT_FRONTEND			0x003E
 #define ARMV8_PMUV3_PERFCTR_STALL_SLOT				0x003F
 
+/* Base of the common events reported in PMCEID{0,1}[63:32] from PMUv3p1 */
+#define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE			0x4000
+
 /* Statistical profiling extension microarchitectural events */
 #define ARMV8_SPE_PERFCTR_SAMPLE_POP				0x4000
 #define ARMV8_SPE_PERFCTR_SAMPLE_FEED				0x4001
@@ -315,4 +318,23 @@
 
 #include <asm/arm_pmuv3.h>
 
+/*
+ * Whether this CPU's PMU implements a common event, as reported by
+ * PMCEID{0,1}: events 0x0000-0x003f in bits [31:0], and from PMUv3p1 events
+ * 0x4000-0x403f in bits [63:32], which read as zero before PMUv3p1.
+ * Must run on the CPU whose PMU is queried.
+ */
+static inline bool pmuv3_event_implemented(u16 event)
+{
+	bool ext = event >= ARMV8_PMUV3_EXT_COMMON_EVENT_BASE;
+	u16 id = ext ? event - ARMV8_PMUV3_EXT_COMMON_EVENT_BASE : event;
+	u64 pmceid;
+
+	if (id >= 64 || !pmuv3_implemented(read_pmuver()))
+		return false;
+
+	pmceid = id < 32 ? read_pmceid0() : read_pmceid1();
+	return pmceid & BIT_ULL(id % 32 + (ext ? 32 : 0));
+}
+
 #endif
-- 
2.52.0