Re: [PATCH v6 07/13] coresight: etm4x: fix inconsistencies with sysfs configuration

[Leo Yan <leo.yan@arm.com>]

On Wed, Apr 22, 2026 at 02:21:57PM +0100, Yeoreum Yun wrote:

[...]

>   - Since active_config and related fields are accessed only by the local CPU
>     in etm4_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
>     remove the lock/unlock from the sysfs enable/disable path and
>     startup/dying_cpu except when to access config fields.

Thanks for writing this up, which is helpful for understanding.

[...]

> @@ -918,40 +948,29 @@ 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);

With the patch [1], we can move cscfg_config_sysfs_get_active_cfg() to
smp call. As a result, all things for enabling cscfg can be in the
same place.

[1] https://lore.kernel.org/linux-arm-kernel/20260511-arm_coresight_path_power_management_improvement-v12-14-1c9dcb1de8c9@arm.com/

> -	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;
>  
>  	/*
>  	 * 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.path = path;
> +	arg.cfg_hash = cfg_hash;
> +	arg.preset = preset;

Connect with the comment above , don't need to pass cfg_hash/preset anymore.

> +	raw_spin_lock(&drvdata->spinlock);
> +	arg.config = drvdata->config;
> +	raw_spin_unlock(&drvdata->spinlock);

Seems to me, this is right way for locking - here we simply use
spinlock for exclusive access config from sysfs knobs.

However, we avoid the config copy and directly access in SMP call?
we still can use the raw spinlock in SMP call.

My suggestion is:

- First use a patch to move the drvdata assignment to SMP call and
  remove spinlock;
- Then, rebase this patch for moving cscfg into SMP call.

If so, we only need add a new field "arg->path", right?


> @@ -1857,13 +1875,11 @@ static int etm4_starting_cpu(unsigned int cpu)
>  	if (!etmdrvdata[cpu])
>  		return 0;
>  
> -	raw_spin_lock(&etmdrvdata[cpu]->spinlock);

With the change [2], the starting and dying functions have been
removed.

If you rebase patches on the top PM series, then you will not bother
this. Anyway, this is right to remove spinlock for hotplug notifiers.

[2] https://lore.kernel.org/linux-arm-kernel/20260511-arm_coresight_path_power_management_improvement-v12-27-1c9dcb1de8c9@arm.com/