[PATCH v11 23/27] coresight: Add PM callbacks for sink device

[Leo Yan]

Unlike system level sinks, per-CPU sinks may lose power during CPU idle
states.  Currently, this applies specifically to TRBE.  This commit
invokes save and restore callbacks for the sink in the CPU PM notifier.

If the sink provides PM callbacks but the source does not, this is
unsafe because the sink cannot be disabled safely unless the source
can also be controlled, so veto low power entry to avoid lockups.

Tested-by: James Clark <james.clark at linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun at arm.com>
Reviewed-by: James Clark <james.clark at linaro.org>
Tested-by: Jie Gan <jie.gan at oss.qualcomm.com>
Signed-off-by: Leo Yan <leo.yan at arm.com>
---
 drivers/hwtracing/coresight/coresight-core.c | 35 ++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
index d65bb2ea7b0560d44abf302a3939b3744ca0c880..b2301ae0fd358242c59b9f4da99faae0db5ff894 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1850,7 +1850,7 @@ static struct coresight_path *coresight_cpu_get_active_path(void)
 /* Return: 1 if PM is required, 0 if skip, or a negative error */
 static int coresight_pm_is_needed(struct coresight_path *path)
 {
-	struct coresight_device *source;
+	struct coresight_device *source, *sink;
 
 	if (this_cpu_read(percpu_pm_failed))
 		return -EIO;
@@ -1859,7 +1859,8 @@ static int coresight_pm_is_needed(struct coresight_path *path)
 		return 0;
 
 	source = coresight_get_source(path);
-	if (!source)
+	sink = coresight_get_sink(path);
+	if (!source || !sink)
 		return 0;
 
 	/* pm_save_disable() and pm_restore_enable() must be paired */
@@ -1867,16 +1868,35 @@ static int coresight_pm_is_needed(struct coresight_path *path)
 	    coresight_ops(source)->pm_restore_enable)
 		return 1;
 
+	/*
+	 * It is not permitted that the source has no callbacks while the sink
+	 * does, as the sink cannot be disabled without disabling the source,
+	 * which may lead to lockups. Fix this by enabling self-hosted PM
+	 * mode for ETM (see etm4_probe()).
+	 */
+	if (coresight_ops(sink)->pm_save_disable &&
+	    coresight_ops(sink)->pm_restore_enable) {
+		pr_warn_once("coresight PM failed: source has no PM callbacks; "
+			     "cannot safely control sink\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
 static int coresight_pm_device_save(struct coresight_device *csdev)
 {
+	if (!csdev || !coresight_ops(csdev)->pm_save_disable)
+		return 0;
+
 	return coresight_ops(csdev)->pm_save_disable(csdev);
 }
 
 static void coresight_pm_device_restore(struct coresight_device *csdev)
 {
+	if (!csdev || !coresight_ops(csdev)->pm_restore_enable)
+		return;
+
 	coresight_ops(csdev)->pm_restore_enable(csdev);
 }
 
@@ -1895,15 +1915,24 @@ static int coresight_pm_save(struct coresight_path *path)
 	to = list_prev_entry(coresight_path_last_node(path), link);
 	coresight_disable_path_from_to(path, from, to);
 
+	/*
+	 * Save the sink. Most sinks do not implement a save callback to avoid
+	 * latency from memory copying. We assume the sink's save and restore
+	 * always succeed.
+	 */
+	coresight_pm_device_save(coresight_get_sink(path));
 	return 0;
 }
 
 static void coresight_pm_restore(struct coresight_path *path)
 {
 	struct coresight_device *source = coresight_get_source(path);
+	struct coresight_device *sink = coresight_get_sink(path);
 	struct coresight_node *from, *to;
 	int ret;
 
+	coresight_pm_device_restore(sink);
+
 	from = coresight_path_first_node(path);
 	/* Enable up to the node before sink */
 	to = list_prev_entry(coresight_path_last_node(path), link);
@@ -1916,6 +1945,8 @@ static void coresight_pm_restore(struct coresight_path *path)
 	return;
 
 path_failed:
+	coresight_pm_device_save(sink);
+
 	pr_err("Failed in coresight PM restore on CPU%d: %d\n",
 	       smp_processor_id(), ret);
 

-- 
2.34.1