linux-kernel - Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user configurable

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Message-ID: <1c0e47a0-1e84-1e02-33dd-76d8eaaa41b0@arm.com>
Date:   Fri, 11 Aug 2023 14:27:11 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>, Jonathan Corbet <corbet@....net>,
        linux-doc@...r.kernel.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user
 configurable



On 8/11/23 14:22, Mike Leach wrote:
> On Fri, 11 Aug 2023 at 04:46, Anshuman Khandual
> <anshuman.khandual@....com> wrote:
>>
>> Cycle counting is enabled, when requested and supported but with a default
>> threshold value ETM_CYC_THRESHOLD_DEFAULT i.e 0x100 getting into TRCCCCTLR,
>> representing the minimum interval between cycle count trace packets.
>>
>> This makes cycle threshold user configurable, from the user space via perf
>> event attributes. Although it falls back using ETM_CYC_THRESHOLD_DEFAULT,
>> in case no explicit request. As expected it creates a sysfs file as well.
>>
>> /sys/bus/event_source/devices/cs_etm/format/cc_threshold
>>
>> New 'cc_threshold' uses 'event->attr.config3' as no more space is available
>> in 'event->attr.config1' or 'event->attr.config2'.
>>
>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>> Cc: Mike Leach <mike.leach@...aro.org>
>> Cc: James Clark <james.clark@....com>
>> Cc: Leo Yan <leo.yan@...aro.org>
>> Cc: coresight@...ts.linaro.org
>> Cc: linux-arm-kernel@...ts.infradead.org
>> Cc: linux-doc@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---
>>  drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
>>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++--
>>  2 files changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> index 5ca6278baff4..09f75dffae60 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> @@ -68,6 +68,7 @@ PMU_FORMAT_ATTR(preset,               "config:0-3");
>>  PMU_FORMAT_ATTR(sinkid,                "config2:0-31");
>>  /* config ID - set if a system configuration is selected */
>>  PMU_FORMAT_ATTR(configid,      "config2:32-63");
>> +PMU_FORMAT_ATTR(cc_threshold,  "config3:0-11");
>>
>>
>>  /*
>> @@ -101,6 +102,7 @@ static struct attribute *etm_config_formats_attr[] = {
>>         &format_attr_preset.attr,
>>         &format_attr_configid.attr,
>>         &format_attr_branch_broadcast.attr,
>> +       &format_attr_cc_threshold.attr,
>>         NULL,
>>  };
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index 1f3d29a639ff..ad28ee044cba 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -644,7 +644,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>         struct etmv4_config *config = &drvdata->config;
>>         struct perf_event_attr *attr = &event->attr;
>>         unsigned long cfg_hash;
>> -       int preset;
>> +       int preset, cc_threshold;
>>
>>         /* Clear configuration from previous run */
>>         memset(config, 0, sizeof(struct etmv4_config));
>> @@ -667,7 +667,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>         if (attr->config & BIT(ETM_OPT_CYCACC)) {
>>                 config->cfg |= TRCCONFIGR_CCI;
>>                 /* TRM: Must program this for cycacc to work */
>> -               config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
>> +               cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
>> +               if (cc_threshold) {
>> +                       if (cc_threshold < drvdata->ccitmin)
>> +                               config->ccctlr = drvdata->ccitmin;
>> +                       else
>> +                               config->ccctlr = cc_threshold;
>> +               } else {
>> +                       config->ccctlr = ETM_CYC_THRESHOLD_DEFAULT;
> 
> Don't normally have {} round a single statement else clause - did

I would believe single statement else clause could have { }, only
when the preceding if clause consists of multiple statements just
to be symmetrical ? 

> checkpatch.pl not object here?

No, it does not object.

> 
> 
> Otherwise
> 
> Reviewed-by: Mike Leach <mike.leach@...aro.org>
> 
>> +               }
>>         }
>>         if (attr->config & BIT(ETM_OPT_TS)) {
>>                 /*
>> --
>> 2.25.1
>>
> 
>