Re: [PATCH V4 2/3] coresight: etm: Make cycle count threshold user configurable

[Suzuki K Poulose]

On 18/08/2023 14:01, Mike Leach wrote:
> On Fri, 18 Aug 2023 at 12:25, Suzuki K Poulose <suzuki.poulose@xxxxxxx> wrote:
> > On 18/08/2023 12:20, Anshuman Khandual 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@xxxxxxx>
> > > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > > Cc: James Clark <james.clark@xxxxxxx>
> > > Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> > > Cc: coresight@xxxxxxxxxxxxxxxx
> > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > > Cc: linux-doc@xxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > Reviewed-by: Mike Leach <mike.leach@xxxxxxxxxx>
> > > Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> > > ---
> > >    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 591fab73ee79..3193dafa7618 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > > @@ -635,7 +635,7 @@ 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));
> > > @@ -658,7 +658,15 @@ 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;
> >
> > Ideally this must be the ccitmin ? Theoretically, default value could be
> > bigger than the minimum value supported by the implementation (i.e.,
> > ccitmin)
> >
> > Suzuki
>
> In order not to change existing behaviour unexpectedly this could be
> re-ordered...
>
> cc_threshold = attr->config3 & ETM_CYC_THRESHOLD_MASK;
> if (!cc_threshold)
>           cc_threshold = ETM_CYC_THRESHOLD_DEFAULT;
> if (cc_threshold < drvdata->ccitmin)
>           cc_threshold = drvdata->ccitmin
> config->ccctlr = cc_threshold;

That sounds better, Thanks Mike

Suzuki

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