Re: [PATCH v4 6/7] coresight: etm4x: Report whether the PMU counts the external outputs

[James Clark <james.clark@linaro.org>]

On 26/10/2026 05:48, Amir Ayupov wrote:
> Some CPUs count the trace unit's external outputs as the PMU common
> events TRCEXTOUT0-3 (0x4010-0x4013), which lets a configuration drive a
> PMU event from trace unit events. Other CPUs, Neoverse N1 for example,
> have no such events, and a feature relying on them would silently do
> nothing there.
> 
> Detect at probe, on the trace unit's CPU, whether the PMU counts every
> external output: the trace unit has an external output for each of its
> events (caps.nr_event), and pmuv3_event_implemented() reports whether
> the PMU implements TRCEXTOUTn. Only check ETE: per its specification, an
> implemented TRCEXTOUTn event counts external output n, while whether that
> output is also an external input is IMPLEMENTATION DEFINED.
> 
> Add a CS_CFG_MATCH_CAP_TRCEXTOUT capability match flag, set it on those
> trace units, and show it in the feature's configfs 'matches' attribute.
> With capabilities matched separately from the device class, a feature
> that requires it only loads on those trace units.
> 
> Assisted-by: Devmate:Opus-5.5
> Signed-off-by: Amir Ayupov <aaupov@fb.com>
> ---
>   .../hwtracing/coresight/coresight-config.h    |  2 ++
>   .../hwtracing/coresight/coresight-etm4x-cfg.c |  6 ++++-
>   .../coresight/coresight-etm4x-core.c          | 26 +++++++++++++++++++
>   drivers/hwtracing/coresight/coresight-etm4x.h |  3 +++
>   .../coresight/coresight-syscfg-configfs.c     |  3 +++
>   5 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
> index 220bc54f8e5e1..4cf53230854d0 100644
> --- a/drivers/hwtracing/coresight/coresight-config.h
> +++ b/drivers/hwtracing/coresight/coresight-config.h
> @@ -38,6 +38,8 @@
>    * a device that matches one of its classes and has all of its capabilities.
>    */
>   #define CS_CFG_MATCH_CAP_MASK		GENMASK_U32(15, 8)
> +/* the PMU counts the trace unit's external outputs as TRCEXTOUTn */
> +#define CS_CFG_MATCH_CAP_TRCEXTOUT	BIT(8)
>   
>   /*
>    * Limit number of presets in a configuration
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index 52cb036bb04b9..9e4dc5950c13d 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> @@ -176,9 +176,13 @@ static int etm4_cfg_load_feature(struct coresight_device *csdev,
>   
>   int etm4_cscfg_register(struct coresight_device *csdev)
>   {
> +	struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>   	struct cscfg_csdev_feat_ops ops;
> +	u32 match_flags = CS_CFG_ETM4_MATCH_FLAGS;
>   
>   	ops.load_feat = &etm4_cfg_load_feature;
> +	if (drvdata->caps.trcextout)
> +		match_flags |= CS_CFG_MATCH_CAP_TRCEXTOUT;
>   
> -	return cscfg_register_csdev(csdev, CS_CFG_ETM4_MATCH_FLAGS, &ops);
> +	return cscfg_register_csdev(csdev, match_flags, &ops);
>   }
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index af017bd8a5477..cb5fbb0279b88 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -30,6 +30,7 @@
>   #include <linux/uaccess.h>
>   #include <linux/perf_event.h>
>   #include <linux/perf/arm_pmu.h>
> +#include <linux/perf/arm_pmuv3.h>
>   #include <linux/platform_device.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/property.h>
> @@ -1399,6 +1400,29 @@ static void etm4_fixup_wrong_ccitmin(struct etmv4_caps *caps)
>   	}
>   }
>   
> +/*
> + * Whether the PMU counts each external output of this trace unit as
> + * TRCEXTOUTn. The trace unit has an external output for each of its events.
> + * Only ETE is checked: per its specification, an implemented TRCEXTOUTn event
> + * counts external output n.
> + *
> + * Must run on the CPU that owns the trace unit.
> + */
> +static bool etm4_pmu_counts_extout(struct etmv4_drvdata *drvdata)
> +{
> +	int n;
> +
> +	if (!etm4x_is_ete(drvdata) || !drvdata->caps.nr_event)
> +		return false;
> +
> +	for (n = 0; n < drvdata->caps.nr_event; n++) {
> +		if (!pmuv3_event_implemented(ARMV8_PMUV3_PERFCTR_TRCEXTOUT0 + n))
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
>   static void etm4_init_arch_data(void *info)
>   {
>   	u32 etmidr0;
> @@ -1562,6 +1586,8 @@ static void etm4_init_arch_data(void *info)
>   	/* NUMCNTR, bits[30:28] number of counters available for tracing */
>   	caps->nr_cntr = FIELD_GET(TRCIDR5_NUMCNTR_MASK, etmidr5);
>   
> +	caps->trcextout = etm4_pmu_counts_extout(drvdata);
> +
>   	coresight_clear_self_claim_tag_unlocked(csa);
>   	etm4_cs_lock(drvdata, csa);
>   	cpu_detect_trace_filtering(drvdata);
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 5417280cdb274..33994ad4b2641 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -868,6 +868,8 @@ enum etm_impdef_type {
>    * @lpoverride:	If the implementation can support low-power state over.
>    * @skip_power_up: Indicates if an implementation can skip powering up
>    *		   the trace unit.
> + * @trcextout:	The trace unit is an ETE whose PMU counts its external
> + *		outputs as TRCEXTOUTn.
>    */
>   struct etmv4_caps {
>   	u8	nr_pe;
> @@ -907,6 +909,7 @@ struct etmv4_caps {
>   	bool	atbtrig : 1;
>   	bool	lpoverride : 1;
>   	bool	skip_power_up : 1;
> +	bool	trcextout : 1;
>   };
>   
>   /**
> diff --git a/drivers/hwtracing/coresight/coresight-syscfg-configfs.c b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> index 2b40e556be872..7b3800138f625 100644
> --- a/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> +++ b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
> @@ -250,6 +250,9 @@ static ssize_t cscfg_feat_matches_show(struct config_item *item, char *page)
>   	if (match_flags & CS_CFG_MATCH_CLASS_SRC_ETM4)
>   		used += scnprintf(page + used, PAGE_SIZE - used, "SRC_ETMV4 ");
>   
> +	if (match_flags & CS_CFG_MATCH_CAP_TRCEXTOUT)
> +		used += scnprintf(page + used, PAGE_SIZE - used, "TRCEXTOUT ");
> +
>   	used += scnprintf(page + used, PAGE_SIZE - used, "\n");
>   	return used;
>   }

Reviewed-by: James Clark <james.clark@linaro.org>