Re: [PATCH RFC V3 4/4] coresight: Have a stab at support for pause / resume

[James Clark <james.clark@arm.com>]

On 15/12/2023 06:42, Adrian Hunter wrote:
> For discussion only, un-tested...
> 

If anyone wants to test Coresight, the diff below is required to get the
most basic use case working. It also probably needs more thought and
some edge case handling:

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index 596c01e37624..bd0767356277 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -556,7 +556,8 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	struct etm_event_data *event_data;
 	struct list_head *path;
 
-	if (mode & PERF_EF_PAUSE && !READ_ONCE(ctxt->pr_allowed))
+	if ((mode & PERF_EF_PAUSE && !READ_ONCE(ctxt->pr_allowed)) ||
+	    event->hw.state == PERF_HES_STOPPED)
 		return;
 
 	WRITE_ONCE(ctxt->pr_allowed, 0);
@@ -573,9 +574,6 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	/* Clear the event_data as this ETM is stopping the trace. */
 	ctxt->event_data = NULL;
 
-	if (event->hw.state == PERF_HES_STOPPED)
-		goto out_pr_allowed;
-
 	/* We must have a valid event_data for a running event */
 	if (WARN_ON(!event_data))
 		return;
@@ -586,7 +584,7 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	 * nothing needs to be torn down other than outputting a
 	 * zero sized record.
 	 */
-	if (handle->event && (mode & PERF_EF_UPDATE) &&
+	if (handle->event && (mode & (PERF_EF_UPDATE | PERF_EF_PAUSE)) &&
 	    !cpumask_test_cpu(cpu, &event_data->mask)) {
 		event->hw.state = PERF_HES_STOPPED;
 		perf_aux_output_end(handle, 0);
@@ -616,7 +614,7 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	 * handle due to lack of buffer space), we don't
 	 * have to do anything here.
 	 */
-	if (handle->event && (mode & PERF_EF_UPDATE)) {
+	if (handle->event && (mode & (PERF_EF_UPDATE | PERF_EF_PAUSE))) {
 		if (WARN_ON_ONCE(handle->event != event))
 			return;
 
@@ -646,7 +644,6 @@ static void etm_event_stop(struct perf_event *event, int mode)
 	/* Disabling the path make its elements available to other sessions */
 	coresight_disable_path(path);
 
-out_pr_allowed:
 	if (mode & PERF_EF_PAUSE)
 		WRITE_ONCE(ctxt->pr_allowed, 1);
 }
@@ -656,7 +653,7 @@ static int etm_event_add(struct perf_event *event, int mode)
 	int ret = 0;
 	struct hw_perf_event *hwc = &event->hw;
 
-	if (mode & PERF_EF_START && !READ_ONCE(event->aux_paused)) {
+	if (mode & PERF_EF_START) {
 		etm_event_start(event, 0);
 		if (hwc->state & PERF_HES_STOPPED)
 			ret = -EINVAL;
-- 
2.34.1