[PATCH v2 5/5] coresight: etm3x: fix inconsistencies with sysfs configration

Yeoreum Yun
2026-04-10T07:43:38Z

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 inconsistencies, the configuration should be separated into:

- active_config, which is applied configuration for the current session
- config, which stores the settings configured via sysfs.

and apply configuration after taking a mode.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
drivers/hwtracing/coresight/coresight-etm.h | 2 ++
.../coresight/coresight-etm3x-core.c | 20 ++++++++++++-------
2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
index 6fda26039db8..9ed5e2361be1 100644
--- a/drivers/hwtracing/coresight/coresight-etm.h
+++ b/drivers/hwtracing/coresight/coresight-etm.h
@@ -241,6 +241,7 @@ 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 {
@@ -256,6 +257,7 @@ 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 b7e977defb1c..0afe2275aa27 100644
--- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
@@ -308,7 +308,7 @@ void etm_config_trace_mode(struct etm_config *config)
static int etm_parse_event_config(struct etm_drvdata *drvdata,
struct perf_event *event)
{
- 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);
@@ -442,24 +442,30 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)

struct etm_enable_arg {
struct etm_drvdata *drvdata;
+ u32 traceid;
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 = drvdata->config;
+ drvdata->traceid = arg->traceid;
+
arg->rc = etm_enable_hw(arg->drvdata);

/* The tracer didn't start */
@@ -514,14 +520,13 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat

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.traceid = path->trace_id;
ret = smp_call_function_single(drvdata->cpu,
etm_enable_sysfs_smp_call, &arg, 1);
if (!ret)
@@ -564,7 +569,7 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
static void etm_disable_hw(struct etm_drvdata *drvdata)
{
int i;
- struct etm_config *config = &drvdata->config;
+ struct etm_config *config = &drvdata->active_config;
struct coresight_device *csdev = drvdata->csdev;

CS_UNLOCK(drvdata->csa.base);
@@ -882,7 +887,8 @@ static int etm_probe(struct amba_device *adev, const struct amba_id *id)
if (etm_arch_supported(drvdata->arch) == false)
return -EINVAL;

- etm_set_default(&drvdata->config);
+ etm_set_default(&drvdata->active_config);
+ drvdata->config = drvdata->active_config;

pdata = coresight_get_platform_data(dev);
if (IS_ERR(pdata))
--
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}