Re: [PATCH 1/2] coresight: etm4x: fix inconsistencies with sysfs configration

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

Hi Levi

On 17/03/2026 18:17, Yeoreum Yun wrote:
> The current ETM4x configuration via sysfs can lead to the following
> inconsistencies:
> 
>    - If a configuration is modified via sysfs while a perf session is
>      active, the running configuration may differ between before
>      a sched-out and after a subsequent sched-in.
> 
>    - Once a perf session is enabled, some read-only register fields
>      (e.g., TRCSSCSR<n>) may not be reported correctly,
>      because drvdata->config is cleared while enabling with perf mode,
>      even though the information was previously read via etm4_init_arch_data().

Thank you for the patch. The patch looks good to me. Some minor comments
below.

> 
> To resolve these inconsistencies, the configuration should be separated into:
> 
>    - active_config, which represents the currently applied configuration

To be more precise, it is the "Applied configuration for the current 
session"

>    - config, which stores the settings configured via sysfs.

While we are at it, should we stop using the drvdata->config for the
"capabilities" for the ETM (e.g., TRCSSCSRn in ss_status ?) Instead
we could save it in "drvdata->ss_status". This keeps everything
separated:

1. Boot time probed capabilities of ETM
2. Sysfs configuration for the next Run
3. Current active configuration for the ETM (sysfs or perf)

Suzuki


> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   .../hwtracing/coresight/coresight-etm4x-cfg.c |  2 +-
>   .../coresight/coresight-etm4x-core.c          | 45 +++++++++++--------
>   drivers/hwtracing/coresight/coresight-etm4x.h |  2 +
>   3 files changed, 30 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index c302072b293a..84213d40d1ae 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> @@ -47,7 +47,7 @@ static int etm4_cfg_map_reg_offset(struct etmv4_drvdata *drvdata,
>   				   struct cscfg_regval_csdev *reg_csdev, u32 offset)
>   {
>   	int err = -EINVAL, idx;
> -	struct etmv4_config *drvcfg = &drvdata->config;
> +	struct etmv4_config *drvcfg = &drvdata->active_config;
>   	u32 off_mask;
>   
>   	if (((offset >= TRCEVENTCTL0R) && (offset <= TRCVIPCSSCTLR)) ||
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index d565a73f0042..c552129c4a0c 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -88,9 +88,11 @@ static int etm4_probe_cpu(unsigned int cpu);
>    */
>   static bool etm4x_sspcicrn_present(struct etmv4_drvdata *drvdata, int n)
>   {
> +	struct etmv4_config *config = &drvdata->active_config;
> +
>   	return (n < drvdata->nr_ss_cmp) &&
>   	       drvdata->nr_pe &&
> -	       (drvdata->config.ss_status[n] & TRCSSCSRn_PC);
> +	       (config->ss_status[n] & TRCSSCSRn_PC);
>   }
>   
>   u64 etm4x_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
> @@ -266,10 +268,11 @@ static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
>   static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   {
>   	u64 trfcr = drvdata->trfcr;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
> -	if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
> +	if (config->mode & ETM_MODE_EXCL_KERN)
>   		trfcr &= ~TRFCR_EL1_ExTRE;
> -	if (drvdata->config.mode & ETM_MODE_EXCL_USER)
> +	if (config->mode & ETM_MODE_EXCL_USER)
>   		trfcr &= ~TRFCR_EL1_E0TRE;
>   
>   	return trfcr;
> @@ -277,7 +280,7 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   
>   /*
>    * etm4x_allow_trace - Allow CPU tracing in the respective ELs,
> - * as configured by the drvdata->config.mode for the current
> + * as configured by the drvdata->active_config.mode for the current
>    * session. Even though we have TRCVICTLR bits to filter the
>    * trace in the ELs, it doesn't prevent the ETM from generating
>    * a packet (e.g, TraceInfo) that might contain the addresses from
> @@ -288,12 +291,13 @@ static u64 etm4x_get_kern_user_filter(struct etmv4_drvdata *drvdata)
>   static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
>   {
>   	u64 trfcr, guest_trfcr;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
>   	/* If the CPU doesn't support FEAT_TRF, nothing to do */
>   	if (!drvdata->trfcr)
>   		return;
>   
> -	if (drvdata->config.mode & ETM_MODE_EXCL_HOST)
> +	if (config->mode & ETM_MODE_EXCL_HOST)
>   		trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
>   	else
>   		trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -301,7 +305,7 @@ static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
>   	write_trfcr(trfcr);
>   
>   	/* Set filters for guests and pass to KVM */
> -	if (drvdata->config.mode & ETM_MODE_EXCL_GUEST)
> +	if (config->mode & ETM_MODE_EXCL_GUEST)
>   		guest_trfcr = drvdata->trfcr & ~(TRFCR_EL1_ExTRE | TRFCR_EL1_E0TRE);
>   	else
>   		guest_trfcr = etm4x_get_kern_user_filter(drvdata);
> @@ -494,7 +498,7 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata)
>   static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>   {
>   	int i, rc;
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   	struct coresight_device *csdev = drvdata->csdev;
>   	struct device *etm_dev = &csdev->dev;
>   	struct csdev_access *csa = &csdev->access;
> @@ -666,7 +670,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata,
>   {
>   	int ctridx;
>   	int rselector;
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
>   	/* No point in trying if we don't have at least one counter */
>   	if (!drvdata->nr_cntr)
> @@ -749,7 +753,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>   {
>   	int ret = 0;
>   	struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   	struct perf_event_attr max_timestamp = {
>   		.ATTR_CFG_FLD_timestamp_CFG = U64_MAX,
>   	};
> @@ -911,14 +915,17 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
>   
>   	/* enable any config activated by configfs */
>   	cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
> +
> +	raw_spin_lock(&drvdata->spinlock);
> +
> +	drvdata->active_config = drvdata->config;
> +
>   	if (cfg_hash) {
>   		ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
>   		if (ret)
>   			return ret;
>   	}
>   
> -	raw_spin_lock(&drvdata->spinlock);
> -
>   	drvdata->trcid = path->trace_id;
>   
>   	/* Tracer will never be paused in sysfs mode */
> @@ -1028,7 +1035,7 @@ static void etm4_disable_trace_unit(struct etmv4_drvdata *drvdata)
>   static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
>   {
>   	u32 control;
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   	struct coresight_device *csdev = drvdata->csdev;
>   	struct csdev_access *csa = &csdev->access;
>   	int i;
> @@ -1374,12 +1381,14 @@ static void etm4_init_arch_data(void *info)
>   	u32 etmidr5;
>   	struct etm4_init_arg *init_arg = info;
>   	struct etmv4_drvdata *drvdata;
> +	struct etmv4_config *config;
>   	struct csdev_access *csa;
>   	struct device *dev = init_arg->dev;
>   	int i;
>   
>   	drvdata = dev_get_drvdata(init_arg->dev);
>   	csa = init_arg->csa;
> +	config = &drvdata->active_config;
>   
>   	/*
>   	 * If we are unable to detect the access mechanism,
> @@ -1440,7 +1449,7 @@ static void etm4_init_arch_data(void *info)
>   
>   	/* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
>   	drvdata->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);
> -	drvdata->config.s_ex_level = drvdata->s_ex_level;
> +	config->s_ex_level = drvdata->s_ex_level;
>   	/* EXLEVEL_NS, bits[23:20] Non-secure state instruction tracing */
>   	drvdata->ns_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_NS_MASK, etmidr3);
>   	/*
> @@ -1491,8 +1500,7 @@ static void etm4_init_arch_data(void *info)
>   	 */
>   	drvdata->nr_ss_cmp = FIELD_GET(TRCIDR4_NUMSSCC_MASK, etmidr4);
>   	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
> -		drvdata->config.ss_status[i] =
> -			etm4x_relaxed_read32(csa, TRCSSCSRn(i));
> +		config->ss_status[i] = etm4x_relaxed_read32(csa, TRCSSCSRn(i));
>   	}
>   	/* NUMCIDC, bits[27:24] number of Context ID comparators for tracing */
>   	drvdata->numcidc = FIELD_GET(TRCIDR4_NUMCIDC_MASK, etmidr4);
> @@ -1685,7 +1693,7 @@ static void etm4_set_default(struct etmv4_config *config)
>   static int etm4_get_next_comparator(struct etmv4_drvdata *drvdata, u32 type)
>   {
>   	int nr_comparator, index = 0;
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   
>   	/*
>   	 * nr_addr_cmp holds the number of comparator _pair_, so time 2
> @@ -1726,7 +1734,7 @@ static int etm4_set_event_filters(struct etmv4_drvdata *drvdata,
>   {
>   	int i, comparator, ret = 0;
>   	u64 address;
> -	struct etmv4_config *config = &drvdata->config;
> +	struct etmv4_config *config = &drvdata->active_config;
>   	struct etm_filters *filters = event->hw.addr_filters;
>   
>   	if (!filters)
> @@ -2246,7 +2254,8 @@ static int etm4_add_coresight_dev(struct etm4_init_arg *init_arg)
>   	if (!desc.name)
>   		return -ENOMEM;
>   
> -	etm4_set_default(&drvdata->config);
> +	etm4_set_default(&drvdata->active_config);
> +	drvdata->config = drvdata->active_config;
>   
>   	pdata = coresight_get_platform_data(dev);
>   	if (IS_ERR(pdata))
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
> index 89d81ce4e04e..76beb896f188 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1022,6 +1022,7 @@ struct etmv4_save_state {
>    *		allows tracing at all ELs. We don't want to compute this
>    *		at runtime, due to the additional setting of TRFCR_CX when
>    *		in EL2. Otherwise, 0.
> + * @active_config:	structure holding current applied configuration parameters.
>    * @config:	structure holding configuration parameters.
>    * @save_state:	State to be preserved across power loss
>    * @skip_power_up: Indicates if an implementation can skip powering up
> @@ -1079,6 +1080,7 @@ struct etmv4_drvdata {
>   	bool				skip_power_up : 1;
>   	bool				paused : 1;
>   	u64				trfcr;
> +	struct etmv4_config		active_config;
>   	struct etmv4_config		config;
>   	struct etmv4_save_state		*save_state;
>   	DECLARE_BITMAP(arch_features, ETM4_IMPDEF_FEATURE_MAX);