linux-kernel - Re: [PATCH] arm64/perf: Replace PMU version number '0' with ID_AA64DFR0_EL1_PMUVer

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Message-ID: <60767243-2f3e-a7aa-06e1-674e43f18e9c@arm.com>
Date:   Mon, 28 Nov 2022 08:36:15 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-arm-kernel@...ts.infradead.org, will@...nel.org,
        Marc Zyngier <maz@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/perf: Replace PMU version number '0' with
 ID_AA64DFR0_EL1_PMUVer_NI



On 11/28/22 08:24, Anshuman Khandual wrote:
> __armv8pmu_probe_pmu() returns if detected PMU is either not implemented or
> implementation defined. Extracted ID_AA64DFR0_EL1_PMUVer value, when PMU is
> not implemented is '0' which can be replaced with ID_AA64DFR0_EL1_PMUVer_NI
> defined as '0b0000'.
> 
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: linux-perf-users@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: linux-arm-kernel@...ts.infradead.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> This applies on v6.1-rc6
> 
>  arch/arm64/kernel/perf_event.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index 85a3aaefc0fb..b638f584b4dd 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -1188,7 +1188,8 @@ static void __armv8pmu_probe_pmu(void *info)
>  	dfr0 = read_sysreg(id_aa64dfr0_el1);
>  	pmuver = cpuid_feature_extract_unsigned_field(dfr0,
>  			ID_AA64DFR0_EL1_PMUVer_SHIFT);
> -	if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF || pmuver == 0)
> +	if (pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF ||
> +	    pmuver == ID_AA64DFR0_EL1_PMUVer_NI)
>  		return;
>  
>  	cpu_pmu->pmuver = pmuver;
> --

+ Marc Zyngier <maz@...nel.org>

There are some KVM related pmuver not-implemented check as well, should they be
replaced in this patch or rather in a separate patch ?

arch/arm64/kvm/pmu-emul.c:      if (pmu->pmuver == 0 || pmu->pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)
arch/arm64/kvm/pmu-emul.c:              if (pmu->pmuver == 0 ||
arch/arm64/kvm/pmu-emul.c:                  pmu->pmuver == ID_AA64DFR0_EL1_PMUVer_IMP_DEF)

- Anshuman