Re: [PATCH v4 5/7] perf: arm_pmuv3: Add pmuv3_event_implemented()

[James Clark]

On 26/10/2026 05:48, Amir Ayupov wrote:
> 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() to the arm64 asm/arm_pmuv3.h, next to
> read_pmceid0() and read_pmceid1(). It 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
> linux/perf/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>
> ---
>   arch/arm64/include/asm/arm_pmuv3.h | 19 +++++++++++++++++++
>   include/linux/perf/arm_pmu.h       |  1 -
>   include/linux/perf/arm_pmuv3.h     |  3 +++
>   3 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/include/asm/arm_pmuv3.h b/arch/arm64/include/asm/arm_pmuv3.h
> index 8a777dec8d88a..acd62c4f16743 100644
> --- a/arch/arm64/include/asm/arm_pmuv3.h
> +++ b/arch/arm64/include/asm/arm_pmuv3.h
> @@ -173,6 +173,25 @@ static inline bool pmuv3_implemented(int pmuver)
>   		 pmuver == ID_AA64DFR0_EL1_PMUVer_NI);
>   }
>   
> +/*
> + * 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));
> +}
> +
>   static inline bool is_pmuv3p4(int pmuver)
>   {
>   	return pmuver >= ID_AA64DFR0_EL1_PMUVer_V3P4;
> 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..c21f185a283d6 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

Reviewed-by: James Clark <james.clark@xxxxxxxxxx>