Re: [PATCH v4 15/15] coresight: Move CPU hotplug callbacks to core layer

On 04/11/2025 3:21 pm, Leo Yan wrote:

This commit moves CPU hotplug callbacks from ETMv4 driver to core layer. The motivation is the core layer can control all components on an activated path rather but not only managing tracer in ETMv4 driver.

The perf event layer will disable CoreSight PMU event 'cs_etm' when hotplug off a CPU. That means a perf mode will be always converted to disabled mode in CPU hotplug. Arm CoreSight CPU hotplug callbacks only need to handle the Sysfs mode and ignore the perf mode.

The core layer disables a source and the path when hotplug-off a CPU.

When hotplug-in a CPU, it does not re-enable even the trace was enabled before hotplug-off, in this case, users are asked to re-enable the trace via Sysfs interface.

Signed-off-by: Leo Yan leo.yan@arm.com

drivers/hwtracing/coresight/coresight-core.c | 41 +++++++++++++++++++++- drivers/hwtracing/coresight/coresight-etm4x-core.c | 37 ------------------- 2 files changed, 40 insertions(+), 38 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c index 7095f9befa98c7d638f857466351ef7cd960fde7..9149f028031808dc2b7285f621b97f3631a02b01 100644 --- a/drivers/hwtracing/coresight/coresight-core.c +++ b/drivers/hwtracing/coresight/coresight-core.c @@ -1726,6 +1726,32 @@ static void coresight_pm_restore(struct coresight_device *csdev) coresight_ops(csdev)->pm_restore_enable(csdev); } +static int coresight_dying_cpu(unsigned int cpu) +{

• struct coresight_device *source = per_cpu(csdev_source, cpu);
• struct coresight_path *path;
• if (!source || !source->path)

• return 0;
  

• /*

• * The perf event layer will disable PMU events in the CPU hotplug.
  

• * CoreSight driver should never handle the CS_MODE_PERF case.
  

• */
  

• if (coresight_get_mode(source) != CS_MODE_SYSFS)

• return 0;
  

• /*

• * Save 'source->path' here, as it will be cleared in
  

• * coresight_disable_source().
  

• */
  

• path = source->path;
• coresight_disable_source(source, NULL);
• coresight_disable_path(path);
• return 0;

If the user is expected to re-enable and this new state is visible, don't you need to use the regular coresight_disable_sysfs() function? It calls coresight_disable_source_sysfs() which updates a refcount.

Maybe you didn't do it because it has a mutex in it? It would be easier to change that to a spinlock or take the mutex in a wrapper function and share the core disabling code with the hotplug path.

+}

• static int coresight_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd, void *v) {

@@ -1757,11 +1783,24 @@ static struct notifier_block coresight_cpu_pm_nb = { static int __init coresight_pm_setup(void) {

• return cpu_pm_register_notifier(&coresight_cpu_pm_nb);

• int ret;
• ret = cpu_pm_register_notifier(&coresight_cpu_pm_nb);
• if (ret)

• return ret;
  

• ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING,

• 			"arm/coresight-core:starting",
  

• 			NULL, coresight_dying_cpu);
  

• if (ret)

• cpu_pm_unregister_notifier(&coresight_cpu_pm_nb);
  

• return ret; }

static void coresight_pm_cleanup(void) {

• cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING); cpu_pm_unregister_notifier(&coresight_cpu_pm_nb); }

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index 7bea3d2c6f49a2169b8e3de1cb07cc22147aae3a..1730cee3c3e1845efb2be815553085aba1246cca 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -1802,33 +1802,6 @@ static int etm4_online_cpu(unsigned int cpu) return 0; } -static int etm4_starting_cpu(unsigned int cpu) -{

• if (!etmdrvdata[cpu])

• return 0;
  

• raw_spin_lock(&etmdrvdata[cpu]->spinlock);
• if (!etmdrvdata[cpu]->os_unlock)

• etm4_os_unlock(etmdrvdata[cpu]);
  

• if (coresight_get_mode(etmdrvdata[cpu]->csdev))

• etm4_enable_hw(etmdrvdata[cpu], true);
  

• raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
• return 0;

-}

-static int etm4_dying_cpu(unsigned int cpu) -{

• if (!etmdrvdata[cpu])

• return 0;
  

• raw_spin_lock(&etmdrvdata[cpu]->spinlock);
• if (coresight_get_mode(etmdrvdata[cpu]->csdev))

• etm4_disable_hw(etmdrvdata[cpu]);
  

• raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
• return 0;

-}

• static bool etm4_need_save_restore_context(struct coresight_device *csdev) { if (pm_save_enable != PARAM_PM_SAVE_SELF_HOSTED)

@@ -1915,13 +1888,6 @@ static int __init etm4_pm_setup(void) { int ret;

• ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING,

• 			"arm/coresight4:starting",
  

• 			etm4_starting_cpu, etm4_dying_cpu);
  

• if (ret)

• return ret;
  

• ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "arm/coresight4:online", etm4_online_cpu, NULL);

@@ -1932,14 +1898,11 @@ static int __init etm4_pm_setup(void) return 0; }

• /* failed dyn state - remove others */
• cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING); return ret; }

static void etm4_pm_clear(void) {

• cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING); if (hp_online) { cpuhp_remove_state_nocalls(hp_online); hp_online = 0;