[PATCH v11 18/27] coresight: Save active path for system tracers

Leo Yan
2026-05-01T16:49:11Z

This commit only set the path pointer for system tracers (e.g. STM) in
coresight_{enable|disable}_source().

Later changes will set the path pointer locally for per-CPU sources.
This is because the mode and path pointer must be set together, so that
they are observed atomically by the CPU PM notifier.

Signed-off-by: Leo Yan <leo.yan@arm.com>
---
drivers/hwtracing/coresight/coresight-core.c | 23 ++++++++++++++++++++++-
include/linux/coresight.h | 2 ++
2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index 308282d2d4611997834bd39dc2de271bfa568ee0..b45fb38eb9d652e44802c23ea4ee3b051d635207 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -478,10 +478,28 @@ int coresight_enable_source(struct coresight_device *csdev,
struct perf_event *event, enum cs_mode mode,
struct coresight_path *path)
{
+ int ret;
+
if (!coresight_is_device_source(csdev))
return -EINVAL;

- return source_ops(csdev)->enable(csdev, event, mode, path);
+ ret = source_ops(csdev)->enable(csdev, event, mode, path);
+ if (ret)
+ return ret;
+
+ /*
+ * Update the path pointer until after the source is enabled to avoid
+ * races where multiple paths attempt to enable the same source.
+ *
+ * Do not set the path pointer here for per-CPU sources; set it locally
+ * on the CPU instead. Otherwise, there is a window where the path is
+ * enabled but the pointer is not yet set, causing CPU PM notifiers to
+ * miss PM operations due to reading a NULL pointer.
+ */
+ if (!coresight_is_percpu_source(csdev))
+ csdev->path = path;
+
+ return 0;
}

void coresight_disable_source(struct coresight_device *csdev, void *data)
@@ -489,6 +507,9 @@ void coresight_disable_source(struct coresight_device *csdev, void *data)
if (!coresight_is_device_source(csdev))
return;

+ if (!coresight_is_percpu_source(csdev))
+ csdev->path = NULL;
+
source_ops(csdev)->disable(csdev, data);
}
EXPORT_SYMBOL_GPL(coresight_disable_source);
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index 5f9d7ea9f5941ab01eb6a084ca558a9417c7727f..58d474b269806d32cad6ed87da96550b06f1f30f 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -257,6 +257,7 @@ struct coresight_trace_id_map {
* by @coresight_ops.
* @access: Device i/o access abstraction for this device.
* @dev: The device entity associated to this component.
+ * @path: Activated path pointer (only used for source device).
* @mode: The device mode, i.e sysFS, Perf or disabled. This is actually
* an 'enum cs_mode' but stored in an atomic type. Access is always
* through atomic APIs, ensuring SMP-safe synchronisation between
@@ -291,6 +292,7 @@ struct coresight_device {
const struct coresight_ops *ops;
struct csdev_access access;
struct device dev;
+ struct coresight_path *path;
atomic_t mode;
int refcnt;
int cpu;

--
2.34.1