Re: [PATCH] coresight: etm: Make cycle count threshold user configurable

[Mike Leach]

Hi Anshuman

On Tue, 8 Aug 2023 at 08:45, Anshuman Khandual
<anshuman.khandual@xxxxxxx> 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
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> Changes in V2:
>

Please ensure that the e-mail title reflects the "v2" nature of this.
e.g. [PATCH v2] ....


> - s/treshhold/threshhold
>
> Changes in V1:
>
> https://lore.kernel.org/all/20230804044720.1478900-1-anshuman.khandual@xxxxxxx/
>
>  Documentation/trace/coresight/coresight.rst        |  2 ++
>  drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
>  drivers/hwtracing/coresight/coresight-etm4x-core.c | 12 ++++++++++--
>  3 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
> index 4a71ea6cb390..a698b07206b5 100644
> --- a/Documentation/trace/coresight/coresight.rst
> +++ b/Documentation/trace/coresight/coresight.rst
> @@ -624,6 +624,8 @@ They are also listed in the folder /sys/bus/event_source/devices/cs_etm/format/
>     * - timestamp
>       - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP
>         <coresight-timestamp>`
> +   * - cc_threshold
> +     - Cycle count threshold value
>
>  How to use the STM module
>  -------------------------

The doc elements here need to be in a separate patch in the set and
additionally sent to doc list and maintainer
(linux-doc@xxxxxxxxxxxxxxx and corbet@xxxxxxx) to be picked up.

> 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 9d186af81ea0..a353c0784bab 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;
> +               }
>         }
>         if (attr->config & BIT(ETM_OPT_TS)) {
>                 /*
> --
> 2.25.1
>

As we are using ccitmin - which I think we must - then we need an
additional patch in the set that implements the errata workaround
mentioned by Al, when setting ccitmin in etm4_init_arch_data().
Perhaps a helper function called from there to read the ID reg unless
one of the errata cores in which case set to 0x4.

Regards

Mike


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