[PATCH v6 12/13] coresight: etm3x: fix inconsistencies with sysfs configuration

Yeoreum Yun
2026-04-22T13:23:02Z

The current ETM3x 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.

To resolve these issues, separate the configuration into:

- active_config: the configuration applied to the current session
- config: the configuration set via sysfs

Additionally:

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

Fixes: 1925a470ce69 ("coresight: etm3x: splitting struct etm_drvdata")
Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
drivers/hwtracing/coresight/coresight-etm.h | 2 +
.../coresight/coresight-etm3x-core.c | 47 +++++++++----------
2 files changed, 25 insertions(+), 24 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
index 932bec82fb47..01f1a7f2559c 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -243,6 +243,7 @@ struct etm_config {
* @boot_enable:true if we should start tracing at boot time.
* @os_unlock: true if access to management registers is allowed.
* @traceid: value of the current ID for this component.
+ * @active_config: structure holding current running configuration parameters.
* @config: structure holding configuration parameters.
*/
struct etm_drvdata {
@@ -258,6 +259,7 @@ struct etm_drvdata {
bool boot_enable;
bool os_unlock;
u32 traceid;
+ struct etm_config active_config;
struct etm_config config;
};

diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
index e42ca346da91..85778e6349f4 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -309,7 +309,7 @@ static int etm_parse_event_config(struct etm_drvdata *drvdata,
struct perf_event *event)
{
const struct etm_caps *caps = &drvdata->caps;
- struct etm_config *config = &drvdata->config;
+ struct etm_config *config = &drvdata->active_config;
struct perf_event_attr *attr = &event->attr;
u8 ts_level;

@@ -368,7 +368,7 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
int i, rc;
u32 etmcr;
const struct etm_caps *caps = &drvdata->caps;
- struct etm_config *config = &drvdata->config;
+ struct etm_config *config = &drvdata->active_config;
struct coresight_device *csdev = drvdata->csdev;

CS_UNLOCK(drvdata->csa.base);
@@ -442,29 +442,38 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)

struct etm_enable_arg {
struct etm_drvdata *drvdata;
+ const struct coresight_path *path;
+ struct etm_config config;
int rc;
};

static void etm_enable_sysfs_smp_call(void *info)
{
struct etm_enable_arg *arg = info;
+ struct etm_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;
}

+ drvdata->active_config = arg->config;
+ drvdata->traceid = arg->path->trace_id;
+
arg->rc = etm_enable_hw(arg->drvdata);

/* The tracer didn't start */
if (arg->rc)
coresight_set_mode(csdev, CS_MODE_DISABLED);
+ else
+ drvdata->sticky_enable = true;
}

static int etm_cpu_id(struct coresight_device *csdev)
@@ -512,33 +521,31 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
struct etm_enable_arg arg = { };
int ret;

- raw_spin_lock(&drvdata->spinlock);
-
- drvdata->traceid = path->trace_id;
-
/*
* Configure the ETM only if the CPU is online. If it isn't online
* hw configuration will take place on the local CPU during bring up.
*/
if (cpu_online(drvdata->cpu)) {
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,
etm_enable_sysfs_smp_call, &arg, 1);
if (!ret)
ret = arg.rc;
- if (!ret)
- drvdata->sticky_enable = true;
} else {
ret = -ENODEV;
}

- if (ret)
- etm_release_trace_id(drvdata);
-
- raw_spin_unlock(&drvdata->spinlock);
-
if (!ret)
dev_dbg(&csdev->dev, "ETM tracing enabled\n");
+ else
+ etm_release_trace_id(drvdata);
+
return ret;
}

@@ -565,7 +572,7 @@ static void etm_disable_hw(struct etm_drvdata *drvdata)
{
int i;
const struct etm_caps *caps = &drvdata->caps;
- struct etm_config *config = &drvdata->config;
+ struct etm_config *config = &drvdata->active_config;
struct coresight_device *csdev = drvdata->csdev;

CS_UNLOCK(drvdata->csa.base);
@@ -636,7 +643,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
* DYING hotplug callback is serviced by the ETM driver.
*/
cpus_read_lock();
- raw_spin_lock(&drvdata->spinlock);

/*
* Executing etm_disable_hw on the cpu whose ETM is being disabled
@@ -645,7 +651,6 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
smp_call_function_single(drvdata->cpu, etm_disable_sysfs_smp_call,
drvdata, 1);

- raw_spin_unlock(&drvdata->spinlock);
cpus_read_unlock();

/*
@@ -711,15 +716,11 @@ static int etm_starting_cpu(unsigned int cpu)
if (!etmdrvdata[cpu])
return 0;

- raw_spin_lock(&etmdrvdata[cpu]->spinlock);
- if (!etmdrvdata[cpu]->os_unlock) {
+ if (!etmdrvdata[cpu]->os_unlock)
etm_os_unlock(etmdrvdata[cpu]);
- etmdrvdata[cpu]->os_unlock = true;
- }

if (coresight_get_mode(etmdrvdata[cpu]->csdev))
etm_enable_hw(etmdrvdata[cpu]);
- raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
return 0;
}

@@ -728,10 +729,8 @@ static int etm_dying_cpu(unsigned int cpu)
if (!etmdrvdata[cpu])
return 0;

- raw_spin_lock(&etmdrvdata[cpu]->spinlock);
if (coresight_get_mode(etmdrvdata[cpu]->csdev))
etm_disable_hw(etmdrvdata[cpu]);
- raw_spin_unlock(&etmdrvdata[cpu]->spinlock);
return 0;