linux-kernel - Re: [PATCH v5 03/22] drivers/perf: riscv: Read upper bits of a firmware counter

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Message-ID: <e95f9821-e83c-4abb-941d-60ce24b9c0a3@rivosinc.com>
Date: Mon, 8 Apr 2024 17:04:41 -0700
From: Atish Patra <atishp@...osinc.com>
To: Andrew Jones <ajones@...tanamicro.com>
Cc: linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
 Conor Dooley <conor.dooley@...rochip.com>, Anup Patel <anup@...infault.org>,
 Ajay Kaher <akaher@...are.com>, Alexandre Ghiti <alexghiti@...osinc.com>,
 Alexey Makhalov <amakhalov@...are.com>, Juergen Gross <jgross@...e.com>,
 kvm-riscv@...ts.infradead.org, kvm@...r.kernel.org,
 linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org,
 Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>,
 Paolo Bonzini <pbonzini@...hat.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Shuah Khan <shuah@...nel.org>,
 virtualization@...ts.linux.dev,
 VMware PV-Drivers Reviewers <pv-drivers@...are.com>,
 Will Deacon <will@...nel.org>, x86@...nel.org
Subject: Re: [PATCH v5 03/22] drivers/perf: riscv: Read upper bits of a
 firmware counter

On 4/4/24 04:02, Andrew Jones wrote:
> On Wed, Apr 03, 2024 at 01:04:32AM -0700, Atish Patra wrote:
>> SBI v2.0 introduced a explicit function to read the upper 32 bits
>> for any firmware counter width that is longer than 32bits.
>> This is only applicable for RV32 where firmware counter can be
>> 64 bit.
>>
>> Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
>> Acked-by: Palmer Dabbelt <palmer@...osinc.com>
>> Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
>> Reviewed-by: Anup Patel <anup@...infault.org>
>> Signed-off-by: Atish Patra <atishp@...osinc.com>
>> ---
>>   drivers/perf/riscv_pmu_sbi.c | 25 ++++++++++++++++++++-----
>>   1 file changed, 20 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
>> index 3e44d2fb8bf8..babf1b9a4dbe 100644
>> --- a/drivers/perf/riscv_pmu_sbi.c
>> +++ b/drivers/perf/riscv_pmu_sbi.c
>> @@ -57,6 +57,8 @@ asm volatile(ALTERNATIVE(						\
>>   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,
>> @@ -511,19 +513,29 @@ 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)
>> +				val |= ((u64)ret.value << 32);
>> +			else
>> +				WARN_ONCE(1, "Unable to read upper 32 bits of firmware counter error: %d\n",
>> +					  sbi_err_map_linux_errno(ret.error));
> 
> I don't think we should use sbi_err_map_linux_errno() in this case since
> we don't have a 1:1 mapping of SBI errors to Linux errors and we don't
> propagate the error as a Linux error. For warnings, it's better to output
> the exact SBI error.
> 

Sure. Fixed it.

>> +		}
>>   	} 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;
>> +			val |= ((u64)riscv_pmu_ctr_read_csr(info.csr + 0x80)) << 32;
>>   	}
>>   
>>   	return val;
>> @@ -1135,6 +1147,9 @@ 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
>>
> 
> Thanks,
> drew