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References: <20230811034600.944386-1-anshuman.khandual@arm.com> <20230811034600.944386-3-anshuman.khandual@arm.com>
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From:   Mike Leach <mike.leach@linaro.org>
Date:   Fri, 11 Aug 2023 09:52:23 +0100
Message-ID: <CAJ9a7VgNmY0_vPfRfz=+hSjbFqnsOAzBgHtZva9fkG04mRaeaQ@mail.gmail.com>
Subject: Re: [PATCH V3 2/3] coresight: etm: Make cycle count threshold user configurable
To:     Anshuman Khandual <anshuman.khandual@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, suzuki.poulose@arm.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        James Clark <james.clark@arm.com>,
        Leo Yan <leo.yan@linaro.org>, Jonathan Corbet <corbet@lwn.net>,
        linux-doc@vger.kernel.org, coresight@lists.linaro.org,
        linux-kernel@vger.kernel.org
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On Fri, 11 Aug 2023 at 04:46, Anshuman Khandual
<anshuman.khandual@arm.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@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: James Clark <james.clark@arm.com>
> Cc: Leo Yan <leo.yan@linaro.org>
> Cc: coresight@lists.linaro.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linux-doc@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.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
checkpatch.pl not object here?


Otherwise

Reviewed-by: Mike Leach <mike.leach@linaro.org>

> +               }
>         }
>         if (attr->config & BIT(ETM_OPT_TS)) {
>                 /*
> --
> 2.25.1
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK