coresight: Save active path for system tracers

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.

Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Tested-by: James Clark <james.clark@linaro.org>
Tested-by: Jie Gan <jie.gan@oss.qualcomm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20260515-arm_coresight_path_power_management_improvement-v14-19-f88c4a3ecfe9@arm.com

1 files changed, 22 insertions, 1 deletions

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index f833b73ebc16..7f6febd20faa 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -487,10 +487,28 @@ 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)
@@ -498,6 +516,9 @@ 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);