On Mon, Jul 02, 2018 at 04:33:29PM -0600, Mathieu Poirier wrote:

SNIP

+static int
+perf_event_process_drv_config(struct perf_event *event, char *config_str)
+{
+	int ret = -EINVAL;
+	void *drv_data;
+
+	/* Make sure ctx.mutex it held */
+	lockdep_assert_held(&event->ctx->mutex);
+
+	/* Children take their configuration from their parent */
+	if (WARN_ON_ONCE(event->parent))
+		goto out;
+
+	drv_data = event->pmu->drv_config_validate(event, config_str);
+	if (!drv_data)
+		goto out;

what's this check for? doc does not mention that,
also the coresight callback does not return NULL

jirka