RE: [PATCH 4/8] coresight: cti: Remove CPU power management code

[Mike Leach]

> -----Original Message-----
> From: Leo Yan <leo.yan@xxxxxxx>
> Sent: Monday, February 9, 2026 6:01 PM
> To: Suzuki Poulose <Suzuki.Poulose@xxxxxxx>; Mike Leach
> <Mike.Leach@xxxxxxx>; James Clark <james.clark@xxxxxxxxxx>; Alexander
> Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>; Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx>; Mathieu Poirier
> <mathieu.poirier@xxxxxxxxxx>; Tingwei Zhang <quic_tingwei@xxxxxxxxxxx>;
> Yingchao Deng <yingchao.deng@xxxxxxxxxxxxxxxx>; Jie Gan
> <jie.gan@xxxxxxxxxxxxxxxx>
> Cc: coresight@xxxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; Leo Yan <Leo.Yan@xxxxxxx>
> Subject: [PATCH 4/8] coresight: cti: Remove CPU power management code
> 
> According Arm ARM, the CTI ASICCTL register:
> 
>   "It is IMPLEMENTATION DEFINED whether ASICCTL is implemented in the
>    Core power domain or in the Debug power domain."
> 
> This is the only CTI register that may reside in the core power domain.
> However, it has been confirmed that Arm designed CTIs place ASICCTL in
> the debug power domain.  Furthermore, ASICCTL is implemented only when
> CTIDEVID.EXTMUXNUM is non-zero, which is a rare case for CPU CTIs.
> 
> For these reasons, it is safe to conclude that all CTI registers are not
> located in the CPU power domain. Therefore, the CTI driver does not need
> CPU power management.
> 
> This commit removes the CPU power management from CTI driver.
> 
> Signed-off-by: Leo Yan <leo.yan@xxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-cti-core.c | 186 +----------------------
>  1 file changed, 3 insertions(+), 183 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-cti-core.c
> b/drivers/hwtracing/coresight/coresight-cti-core.c
> index
> 1950e9b757ae4879a2671ddaf5675c54aa7956d5..3becef607e5ec5225cb6f
> d616da804903651fdf1 100644
> --- a/drivers/hwtracing/coresight/coresight-cti-core.c
> +++ b/drivers/hwtracing/coresight/coresight-cti-core.c
> @@ -42,12 +42,6 @@ static DEFINE_MUTEX(ect_mutex);
>  #define csdev_to_cti_drvdata(csdev)	\
>  	dev_get_drvdata(csdev->dev.parent)
> 
> -/* power management handling */
> -static int nr_cti_cpu;
> -
> -/* quick lookup list for CPU bound CTIs when power handling */
> -static struct cti_drvdata *cti_cpu_drvdata[NR_CPUS];
> -
>  /*
>   * CTI naming. CTI bound to cores will have the name cti_cpu<N> where
>   * N is the CPU ID. System CTIs will have the name cti_sys<I> where I
> @@ -113,28 +107,6 @@ static int cti_enable_hw(struct cti_drvdata *drvdata)
>  	return 0;
>  }
> 
> -/* re-enable CTI on CPU when using CPU hotplug */
> -static void cti_cpuhp_enable_hw(struct cti_drvdata *drvdata)
> -{
> -	struct cti_config *config = &drvdata->config;
> -
> -	guard(raw_spinlock_irqsave)(&drvdata->spinlock);
> -
> -	config->hw_powered = true;
> -
> -	/* no need to do anything if no enable request */
> -	if (!drvdata->config.enable_req_count)
> -		return;
> -
> -	/* try to claim the device */
> -	if (coresight_claim_device(drvdata->csdev))
> -		return;
> -
> -	cti_write_all_hw_regs(drvdata);
> -	config->hw_enabled = true;
> -	return;
> -}
> -
>  /* disable hardware */
>  static int cti_disable_hw(struct cti_drvdata *drvdata)
>  {
> @@ -652,146 +624,6 @@ static void cti_remove_conn_xrefs(struct
> cti_drvdata *drvdata)
>  	}
>  }
> 
> -/** cti PM callbacks **/
> -static int cti_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
> -			     void *v)
> -{
> -	struct cti_drvdata *drvdata;
> -	struct coresight_device *csdev;
> -	unsigned int cpu = smp_processor_id();
> -	int notify_res = NOTIFY_OK;
> -
> -	if (!cti_cpu_drvdata[cpu])
> -		return NOTIFY_OK;
> -
> -	drvdata = cti_cpu_drvdata[cpu];
> -	csdev = drvdata->csdev;
> -
> -	if (WARN_ON_ONCE(drvdata->ctidev.cpu != cpu))
> -		return NOTIFY_BAD;
> -
> -	guard(raw_spinlock_irqsave)(&drvdata->spinlock);
> -
> -	switch (cmd) {
> -	case CPU_PM_ENTER:
> -		/* CTI regs all static - we have a copy & nothing to save */
> -		drvdata->config.hw_powered = false;
> -		if (drvdata->config.hw_enabled)
> -			coresight_disclaim_device(csdev);
> -		break;
> -
> -	case CPU_PM_ENTER_FAILED:
> -		drvdata->config.hw_powered = true;
> -		if (drvdata->config.hw_enabled) {
> -			if (coresight_claim_device(csdev))
> -				drvdata->config.hw_enabled = false;
> -		}
> -		break;
> -
> -	case CPU_PM_EXIT:
> -		/* write hardware registers to re-enable. */
> -		drvdata->config.hw_powered = true;
> -		drvdata->config.hw_enabled = false;
> -
> -		/* check enable reference count to enable HW */
> -		if (drvdata->config.enable_req_count) {
> -			/* check we can claim the device as we re-power */
> -			if (coresight_claim_device(csdev))
> -				goto cti_notify_exit;
> -
> -			drvdata->config.hw_enabled = true;
> -			cti_write_all_hw_regs(drvdata);
> -		}
> -		break;
> -
> -	default:
> -		notify_res = NOTIFY_DONE;
> -		break;
> -	}
> -
> -cti_notify_exit:
> -	return notify_res;
> -}
> -
> -static struct notifier_block cti_cpu_pm_nb = {
> -	.notifier_call = cti_cpu_pm_notify,
> -};
> -
> -/* CPU HP handlers */
> -static int cti_starting_cpu(unsigned int cpu)
> -{
> -	struct cti_drvdata *drvdata = cti_cpu_drvdata[cpu];
> -
> -	if (!drvdata)
> -		return 0;
> -
> -	cti_cpuhp_enable_hw(drvdata);
> -	return 0;
> -}
> -
> -static int cti_dying_cpu(unsigned int cpu)
> -{
> -	struct cti_drvdata *drvdata = cti_cpu_drvdata[cpu];
> -
> -	if (!drvdata)
> -		return 0;
> -
> -	guard(raw_spinlock_irqsave)(&drvdata->spinlock);
> -
> -	drvdata->config.hw_powered = false;
> -	if (drvdata->config.hw_enabled)
> -		coresight_disclaim_device(drvdata->csdev);
> -
> -	return 0;
> -}
> -
> -static int cti_pm_setup(struct cti_drvdata *drvdata)
> -{
> -	int ret;
> -
> -	if (drvdata->ctidev.cpu == -1)
> -		return 0;
> -
> -	if (nr_cti_cpu)
> -		goto done;
> -
> -	cpus_read_lock();
> -	ret = cpuhp_setup_state_nocalls_cpuslocked(
> -			CPUHP_AP_ARM_CORESIGHT_CTI_STARTING,
> -			"arm/coresight_cti:starting",
> -			cti_starting_cpu, cti_dying_cpu);
> -	if (ret) {
> -		cpus_read_unlock();
> -		return ret;
> -	}
> -
> -	ret = cpu_pm_register_notifier(&cti_cpu_pm_nb);
> -	cpus_read_unlock();
> -	if (ret) {
> -
> 	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_CTI_STA
> RTING);
> -		return ret;
> -	}
> -
> -done:
> -	nr_cti_cpu++;
> -	cti_cpu_drvdata[drvdata->ctidev.cpu] = drvdata;
> -
> -	return 0;
> -}
> -
> -/* release PM registrations */
> -static void cti_pm_release(struct cti_drvdata *drvdata)
> -{
> -	if (drvdata->ctidev.cpu == -1)
> -		return;
> -
> -	cti_cpu_drvdata[drvdata->ctidev.cpu] = NULL;
> -	if (--nr_cti_cpu == 0) {
> -		cpu_pm_unregister_notifier(&cti_cpu_pm_nb);
> -
> 	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_CTI_STA
> RTING);
> -	}
> -}
> -
>  /** cti ect operations **/
>  int cti_enable(struct coresight_device *csdev, enum cs_mode mode,
>  	       struct coresight_path *path)
> @@ -827,7 +659,6 @@ static void cti_device_release(struct device *dev)
>  	struct cti_drvdata *ect_item, *ect_tmp;
> 
>  	mutex_lock(&ect_mutex);
> -	cti_pm_release(drvdata);
> 
>  	/* remove from the list */
>  	list_for_each_entry_safe(ect_item, ect_tmp, &ect_net, node) {
> @@ -906,17 +737,12 @@ static int cti_probe(struct amba_device *adev,
> const struct amba_id *id)
>  	if (!cti_desc.name)
>  		return -ENOMEM;
> 
> -	/* setup CPU power management handling for CPU bound CTI
> devices. */
> -	ret = cti_pm_setup(drvdata);
> -	if (ret)
> -		return ret;
> -
>  	/* create dynamic attributes for connections */
>  	ret = cti_create_cons_sysfs(dev, drvdata);
>  	if (ret) {
>  		dev_err(dev, "%s: create dynamic sysfs entries failed\n",
>  			cti_desc.name);
> -		goto pm_release;
> +		return ret;
>  	}
> 
>  	/* set up coresight component description */
> @@ -929,10 +755,8 @@ static int cti_probe(struct amba_device *adev, const
> struct amba_id *id)
> 
>  	coresight_clear_self_claim_tag(&cti_desc.access);
>  	drvdata->csdev = coresight_register(&cti_desc);
> -	if (IS_ERR(drvdata->csdev)) {
> -		ret = PTR_ERR(drvdata->csdev);
> -		goto pm_release;
> -	}
> +	if (IS_ERR(drvdata->csdev))
> +		return PTR_ERR(drvdata->csdev);
> 
>  	/* add to list of CTI devices */
>  	mutex_lock(&ect_mutex);
> @@ -949,10 +773,6 @@ static int cti_probe(struct amba_device *adev, const
> struct amba_id *id)
>  	pm_runtime_put(&adev->dev);
>  	dev_info(&drvdata->csdev->dev, "CTI initialized\n");
>  	return 0;
> -
> -pm_release:
> -	cti_pm_release(drvdata);
> -	return ret;
>  }
> 
>  static struct amba_cs_uci_id uci_id_cti[] = {
> 
> --
> 2.34.1
Reviewed-by: Mike Leach <mike.leach@xxxxxxx>