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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

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

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