Subject: Re: [PATCH v7 08/13] coresight: etm4x: fix inconsistencies with sysfs configuration

From: Leo Yan <[email-masked]>
Date: Thu, 28 May 2026 15:09:43 +0100

On Tue, May 19, 2026 at 04:48:07PM +0100, Yeoreum Yun wrote:

[...]

> --- 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;

Wouldn't it make more sense to keep using drvdata->config for cfgfs?
This would avoid cfgfs updating the active configuration while a session
is enabled.

My understanding is after refactoring cfgfs, we will never expose
active_config or config anymore so this should not an issue. Before
that, maybe we just keep to use config so can avoid mess.

>  	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 9b477b36b432..f0a9f2ef4b27 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -243,6 +243,7 @@ void etm4_release_trace_id(struct etmv4_drvdata *drvdata)
>  struct etm4_enable_arg {
>  	struct etmv4_drvdata *drvdata;
>  	struct coresight_path *path;
> +	struct etmv4_config config;
>  	int rc;
>  };
>  
> @@ -268,10 +269,11 @@ 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;
> @@ -279,7 +281,7 @@ 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
> @@ -290,12 +292,13 @@ 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);
> @@ -303,7 +306,7 @@ 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);
> @@ -497,7 +500,7 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
>  {
>  	int i, rc;
>  	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 device *etm_dev = &csdev->dev;
>  	struct csdev_access *csa = &csdev->access;
> @@ -618,27 +621,53 @@ 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;
> +	unsigned long cfg_hash;
> +	int preset;
>  
>  	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);
> +	/* enable any config activated by configfs */
> +	cscfg_config_sysfs_get_active_cfg(&cfg_hash, &preset);
>  
> -	/* The tracer didn't start */
> +	drvdata->active_config = arg->config;

Can move this down to just before drvdata->trcid assignment so cscfg
operations can be put together?

> +
> +	if (cfg_hash) {
> +		arg->rc = cscfg_csdev_enable_active_config(csdev,
> +							   cfg_hash,
> +							   preset);
> +		if (arg->rc)
> +			goto err;
> +	}
> +
> +	drvdata->trcid = arg->path->trace_id;
> +
> +	/* Tracer will never be paused in sysfs mode */
> +	drvdata->paused = false;
> +
> +	arg->rc = etm4_enable_hw(drvdata);
>  	if (arg->rc) {
> -		coresight_set_mode(csdev, CS_MODE_DISABLED);
> -		return;
> +		cscfg_csdev_disable_active_config(csdev);
> +		goto err;

Add a new goto tag (like err_enable_hw) for the disable_active_config
rollback?

>  	}
>  
> +	drvdata->sticky_enable = true;
>  	csdev->path = arg->path;
> +
> +	return;
> +err:
> +	/* The tracer didn't start */
> +	coresight_set_mode(csdev, CS_MODE_DISABLED);
>  }
>  
>  /*
> @@ -676,7 +705,7 @@ 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)
> @@ -760,7 +789,7 @@ 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,
>  	};
> @@ -922,25 +951,7 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
>  {
>  	struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>  	struct etm4_enable_arg arg = { };
> -	unsigned long cfg_hash;
> -	int ret, preset;
> -
> -	/* 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) {
> -			etm4_release_trace_id(drvdata);
> -			return ret;
> -		}
> -	}
> -
> -	raw_spin_lock(&drvdata->spinlock);
> -
> -	drvdata->trcid = path->trace_id;
> -
> -	/* Tracer will never be paused in sysfs mode */
> -	drvdata->paused = false;
> +	int ret;
>  
>  	/*
>  	 * Executing etm4_enable_hw on the cpu whose ETM is being enabled
> @@ -948,20 +959,20 @@ static int etm4_enable_sysfs(struct coresight_device *csdev, struct coresight_pa
>  	 */
>  	arg.drvdata = drvdata;
>  	arg.path = path;
> +
> +	raw_spin_lock(&drvdata->spinlock);
> +	arg.config = drvdata->config;
> +	raw_spin_unlock(&drvdata->spinlock);
> +
>  	ret = smp_call_function_single(drvdata->cpu,
>  				       etm4_enable_sysfs_smp_call, &arg, 1);
>  	if (!ret)
>  		ret = arg.rc;
>  	if (!ret)
> -		drvdata->sticky_enable = true;
> -
> -	if (ret)
> +		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> +	else
>  		etm4_release_trace_id(drvdata);
>  
> -	raw_spin_unlock(&drvdata->spinlock);
> -
> -	if (!ret)
> -		dev_dbg(&csdev->dev, "ETM tracing enabled\n");
>  	return ret;
>  }
>  
> @@ -1048,7 +1059,7 @@ 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;
> @@ -1091,6 +1102,8 @@ static void etm4_disable_sysfs_smp_call(void *info)
>  	etm4_disable_hw(drvdata);
>  
>  	drvdata->csdev->path = NULL;
> +	cscfg_csdev_disable_active_config(drvdata->csdev);

Move cscfg_csdev_disable_active_config() just after etm4_disable_hw() so
the sequence is consistent with perf mode.

[...]

> @@ -1449,7 +1458,7 @@ 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;

config->s_ex_level is redundant and not really a configuration item.
We should use caps->s_ex_level instead of config->s_ex_level wherever
it is used.

Thanks,
Leo