Re: [PATCH v3 3/5] coresight: etm4x: fix inconsistencies with sysfs configration

[Jie Gan <jie.gan@oss.qualcomm.com>]

Hi Yeoreum,

On 4/13/2026 1:55 AM, 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.
> 
>    - If a perf session and sysfs session tries to enable concurrently,
>      configuration from configfs could be corrupted.
> 
>    - There is chance to corrupt drvdata->config if perf session tries
>      to enabled among handling cscfg_csdev_disable_active_config()
>      in etm4_disable_sysfs().
> 
> To resolve these inconsistencies, the configuration should be separated into:
> 
>    - active_config, which is applied configuration for the current session
>    - config, which stores the settings configured via sysfs.
> 
> and apply configuration from configfs after taking a mode.

typo in subject:
s/configration/configuration

> 
> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> ---
>   .../hwtracing/coresight/coresight-etm4x-cfg.c |  2 +-
>   .../coresight/coresight-etm4x-core.c          | 74 ++++++++++++-------
>   drivers/hwtracing/coresight/coresight-etm4x.h |  2 +
>   3 files changed, 49 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
> index d14d7c8a23e5..0553771d04e7 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;

<...>

>   	struct device *etm_dev = &csdev->dev;
>   	struct csdev_access *csa = &csdev->access;
> @@ -616,19 +621,36 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>   static void etm4_enable_sysfs_smp_call(void *info)
>   {
>   	struct etm4_enable_arg *arg = info;
> +	struct etmv4_drvdata *drvdata;
>   	struct coresight_device *csdev;
>   
>   	if (WARN_ON(!arg))
>   		return;
>   
> -	csdev = arg->drvdata->csdev;
> +	drvdata = arg->drvdata;
> +	csdev = drvdata->csdev;
>   	if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
>   		/* Someone is already using the tracer */
>   		arg->rc = -EBUSY;
>   		return;
>   	}
>   
> -	arg->rc = etm4_enable_hw(arg->drvdata);
> +	drvdata->active_config = drvdata->config;
> +
> +	if (arg->cfg_hash) {
> +		arg->rc = cscfg_csdev_enable_active_config(csdev,
> +							   arg->cfg_hash,
> +							   arg->preset);
> +		if (arg->rc)

we need reset the mode once enable failed before return.
coresight_set_mode(csdev, CS_MODE_DISABLED);

Thanks,
Jie

> +			return;
> +	}
> +
> +	drvdata->trcid = arg->trace_id;
> +
> +	/* Tracer will never be paused in sysfs mode */
> +	drvdata->paused = false;
> +
> +	arg->rc = etm4_enable_hw(drvdata);
>   
>   	/* The tracer didn't start */
>   	if (arg->rc)
> @@ -670,7 +692,7 @@ static int etm4_config_timestamp_event(struct etmv4_drvdata *drvdata,
>   	int ctridx;
>   	int rselector;
>   	const struct etmv4_caps *caps = &drvdata->caps;
> -	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 (!caps->nr_cntr)
> @@ -754,7 +776,7 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>   	int ret = 0;
>   	struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>   	const struct etmv4_caps *caps = &drvdata->caps;
> -	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,
>   	};
> @@ -916,24 +938,18 @@ 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);
> -	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 */
> -	drvdata->paused = false;
> -
>   	/*
>   	 * Executing etm4_enable_hw on the cpu whose ETM is being enabled
>   	 * ensures that register writes occur when cpu is powered.
>   	 */
>   	arg.drvdata = drvdata;
> +	arg.cfg_hash = cfg_hash;
> +	arg.preset = preset;
> +	arg.trace_id = path->trace_id;
> +
>   	ret = smp_call_function_single(drvdata->cpu,
>   				       etm4_enable_sysfs_smp_call, &arg, 1);
>   	if (!ret)
> @@ -1034,7 +1050,7 @@ static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
>   {
>   	u32 control;
>   	const struct etmv4_caps *caps = &drvdata->caps;
> -	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;
> @@ -1070,6 +1086,8 @@ static void etm4_disable_sysfs_smp_call(void *info)
>   
>   	etm4_disable_hw(drvdata);
>   
> +	cscfg_csdev_disable_active_config(drvdata->csdev);
> +
>   	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
>   }
>   
> @@ -1130,9 +1148,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
>   				 drvdata, 1);
>   
>   	raw_spin_unlock(&drvdata->spinlock);
> -
> -	cscfg_csdev_disable_active_config(csdev);
> -
>   	cpus_read_unlock();
>   
>   	/*
> @@ -1375,6 +1390,7 @@ static void etm4_init_arch_data(void *info)
>   	struct etm4_init_arg *init_arg = info;
>   	struct etmv4_drvdata *drvdata;
>   	struct etmv4_caps *caps;
> +	struct etmv4_config *config;
>   	struct csdev_access *csa;
>   	struct device *dev = init_arg->dev;
>   	int i;
> @@ -1382,6 +1398,7 @@ static void etm4_init_arch_data(void *info)
>   	drvdata = dev_get_drvdata(init_arg->dev);
>   	caps = &drvdata->caps;
>   	csa = init_arg->csa;
> +	config = &drvdata->active_config;
>   
>   	/*
>   	 * If we are unable to detect the access mechanism,
> @@ -1442,7 +1459,7 @@ static void etm4_init_arch_data(void *info)
>   
>   	/* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
>   	caps->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);
> -	drvdata->config.s_ex_level = caps->s_ex_level;
> +	config->s_ex_level = caps->s_ex_level;
>   	/* EXLEVEL_NS, bits[23:20] Non-secure state instruction tracing */
>   	caps->ns_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_NS_MASK, etmidr3);
>   	/*
> @@ -1687,7 +1704,7 @@ 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
> @@ -1728,7 +1745,7 @@ 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)
> @@ -2250,7 +2267,8 @@ 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 3cc1ca76c933..b943c28c9c71 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
> @@ -1069,6 +1069,7 @@ 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
>    * @paused:	Indicates if the trace unit is paused.
> @@ -1089,6 +1090,7 @@ struct etmv4_drvdata {
>   	bool				os_unlock : 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);