Re: [PATCH v4 03/15] drivers/perf: riscv: Read upper bits of a firmware counter

[Andrew Jones]

On Wed, Feb 28, 2024 at 05:01:18PM -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.

firmware

> This is only applicable for RV32 where firmware counter can be
> 64 bit.
> 
> Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
> Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx>
> ---
>  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..ea0fdb589f0d 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 0;
> +
> +		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)

Getting an error here indicates a buggy SBI. Maybe we should have a
warn-once?

> +				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);
> -- 
> 2.34.1
>

Either way,

Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>