linux-kernel - Re: [v1 03/10] drivers/perf: riscv: Read upper bits of a firmware counter

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Message-ID: <mhng-94cdfcf4-01c1-493c-a23e-32bc8b391aad@palmer-ri-x1c9a>
Date: Thu, 28 Dec 2023 17:44:48 -0800 (PST)
From: Palmer Dabbelt <palmer@...belt.com>
To: Atish Patra <atishp@...osinc.com>
CC: linux-kernel@...r.kernel.org, Atish Patra <atishp@...osinc.com>,
  aou@...s.berkeley.edu, alexghiti@...osinc.com, ajones@...tanamicro.com, anup@...infault.org,
  atishp@...shpatra.org, Conor Dooley <conor.dooley@...rochip.com>, guoren@...nel.org, uwu@...nowy.me,
  kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org, linux-riscv@...ts.infradead.org,
  Mark Rutland <mark.rutland@....com>, Paul Walmsley <paul.walmsley@...ive.com>, Will Deacon <will@...nel.org>
Subject:     Re: [v1 03/10] drivers/perf: riscv: Read upper bits of a firmware counter

On Mon, 18 Dec 2023 02:41:00 PST (-0800), Atish Patra wrote:
> SBI v2.0 introduced a explicit function to read the upper 32 bits
> for any firmwar counter width that is longer than 32bits.
> This is only applicable for RV32 where firmware counter can be
> 64 bit.
>
> Signed-off-by: Atish Patra <atishp@...osinc.com>
> ---
>  drivers/perf/riscv_pmu_sbi.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
> index 16acd4dcdb96..646604f8c0a5 100644
> --- a/drivers/perf/riscv_pmu_sbi.c
> +++ b/drivers/perf/riscv_pmu_sbi.c
> @@ -35,6 +35,8 @@
>  PMU_FORMAT_ATTR(event, "config:0-47");
>  PMU_FORMAT_ATTR(firmware, "config:63");
>
> +static bool sbi_v2_available;
> +
>  static struct attribute *riscv_arch_formats_attr[] = {
>  	&format_attr_event.attr,
>  	&format_attr_firmware.attr,
> @@ -488,16 +490,23 @@ static u64 pmu_sbi_ctr_read(struct perf_event *event)
>  	struct hw_perf_event *hwc = &event->hw;
>  	int idx = hwc->idx;
>  	struct sbiret ret;
> -	union sbi_pmu_ctr_info info;
>  	u64 val = 0;
> +	union sbi_pmu_ctr_info info = pmu_ctr_list[idx];
>
>  	if (pmu_sbi_is_fw_event(event)) {
>  		ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_FW_READ,
>  				hwc->idx, 0, 0, 0, 0, 0);
> -		if (!ret.error)
> -			val = ret.value;
> +		if (ret.error)
> +			return val;
> +
> +		val = ret.value;
> +		if (IS_ENABLED(CONFIG_32BIT) && sbi_v2_available && info.width >= 32) {
> +			ret = sbi_ecall(SBI_EXT_PMU, SBI_EXT_PMU_COUNTER_FW_READ_HI,
> +					hwc->idx, 0, 0, 0, 0, 0);
> +			if (!ret.error)
> +				val |= ((u64)ret.value << 32);
> +		}
>  	} else {
> -		info = pmu_ctr_list[idx];
>  		val = riscv_pmu_ctr_read_csr(info.csr);
>  		if (IS_ENABLED(CONFIG_32BIT))
>  			val = ((u64)riscv_pmu_ctr_read_csr(info.csr + 0x80)) << 31 | val;
> @@ -1108,6 +1117,9 @@ static int __init pmu_sbi_devinit(void)
>  		return 0;
>  	}
>
> +	if (sbi_spec_version >= sbi_mk_version(2, 0))
> +		sbi_v2_available = true;
> +
>  	ret = cpuhp_setup_state_multi(CPUHP_AP_PERF_RISCV_STARTING,
>  				      "perf/riscv/pmu:starting",
>  				      pmu_sbi_starting_cpu, pmu_sbi_dying_cpu);

Acked-by: Palmer Dabbelt <palmer@...osinc.com>