media: v4l2-subdev: Document and enforce .s_stream() requirements

The subdev .s_stream() operation must not be called to start an already
started subdev, or stop an already stopped one. This requirement has
never been formally documented. Fix it, and catch possible offenders
with a WARN_ON() in the call_s_stream() wrapper.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

1 files changed, 16 insertions, 1 deletions

diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index b92348ad61f6..32b7d9cd43e6 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -359,6 +359,18 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
 {
 	int ret;
 
+	/*
+	 * The .s_stream() operation must never be called to start or stop an
+	 * already started or stopped subdev. Catch offenders but don't return
+	 * an error yet to avoid regressions.
+	 *
+	 * As .s_stream() is mutually exclusive with the .enable_streams() and
+	 * .disable_streams() operation, we can use the enabled_streams field
+	 * to store the subdev streaming state.
+	 */
+	if (WARN_ON(!!sd->enabled_streams == !!enable))
+		return 0;
+
 #if IS_REACHABLE(CONFIG_LEDS_CLASS)
 	if (!IS_ERR_OR_NULL(sd->privacy_led)) {
 		if (enable)
@@ -372,9 +384,12 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
 
 	if (!enable && ret < 0) {
 		dev_warn(sd->dev, "disabling streaming failed (%d)\n", ret);
-		return 0;
+		ret = 0;
 	}
 
+	if (!ret)
+		sd->enabled_streams = enable ? BIT(0) : 0;
+
 	return ret;
 }