[RFC 1/1] v4l: async: Add some debug prints

[Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>]

Just add some debug prints for V4L2 async sub-device matching process. These
might come useful in figuring out why things don't work as expected.

Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
---
Frieder,

Can you try this? It prints what is being matched with what. Perhaps this
could be merged in a bit more refined form if it proves useful.

Not tested in any way.

 drivers/media/v4l2-core/v4l2-async.c | 41 ++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 2f1b718a9189..6c13a9488415 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -86,13 +86,18 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
 	bool sd_fwnode_is_ep;
 	struct device *dev;
 
+	dev_dbg(sd->dev, "async fwnode match %pfw vs. %pfw\n", sd_fwnode,
+		asd->match.fwnode);
+
 	/*
 	 * Both the subdev and the async subdev can provide either an endpoint
 	 * fwnode or a device fwnode. Start with the simple case of direct
 	 * fwnode matching.
 	 */
-	if (sd_fwnode == asd->match.fwnode)
+	if (sd_fwnode == asd->match.fwnode) {
+		dev_dbg(sd->dev, "true\n");
 		return true;
+	}
 
 	/*
 	 * Otherwise, check if the sd fwnode and the asd fwnode refer to an
@@ -105,8 +110,12 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
 	sd_fwnode_is_ep = fwnode_graph_is_endpoint(sd_fwnode);
 	asd_fwnode_is_ep = fwnode_graph_is_endpoint(asd->match.fwnode);
 
-	if (sd_fwnode_is_ep == asd_fwnode_is_ep)
+	dev_dbg(sd->dev, "async fwnode match %pfw vs. %pfw\n", sd_fwnode,
+		asd->match.fwnode);
+	if (sd_fwnode_is_ep == asd_fwnode_is_ep) {
+		dev_dbg(sd->dev, "unmatching node types (false)\n");
 		return false;
+	}
 
 	/*
 	 * The sd and asd fwnodes are of different types. Get the device fwnode
@@ -120,10 +129,15 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
 		other_fwnode = sd_fwnode;
 	}
 
+	dev_dbg(sd->dev, "async fwnode (compat) match %pfw vs. %pfw\n",
+		dev_fwnode, other_fwnode);
+
 	fwnode_handle_put(dev_fwnode);
 
-	if (dev_fwnode != other_fwnode)
+	if (dev_fwnode != other_fwnode) {
+		dev_dbg(sd->dev, "false\n");
 		return false;
+	}
 
 	/*
 	 * We have a heterogeneous match. Retrieve the struct device of the side
@@ -143,6 +157,8 @@ match_fwnode_one(struct v4l2_async_notifier *notifier,
 			   dev->driver->name);
 	}
 
+	dev_dbg(sd->dev, "true\n");
+
 	return true;
 }
 
@@ -255,7 +271,10 @@ v4l2_async_nf_can_complete(struct v4l2_async_notifier *notifier)
 			v4l2_async_find_subdev_notifier(sd);
 
 		if (subdev_notifier &&
-		    !v4l2_async_nf_can_complete(subdev_notifier))
+		    !v4l2_async_nf_can_complete(subdev_notifier)) {
+			if (subdev_notifier->sd)
+				deb_dbg(subdev_notifier->sd->dev,
+					"cannot complete\n");
 			return false;
 	}
 
@@ -273,18 +292,27 @@ v4l2_async_nf_try_complete(struct v4l2_async_notifier *notifier)
 	if (!list_empty(&notifier->waiting))
 		return 0;
 
+	if (notifier->sd)
+		deb_dbg(notifier->sd->dev, "trying to complete\n");
+
 	/* Check the entire notifier tree; find the root notifier first. */
 	while (notifier->parent)
 		notifier = notifier->parent;
 
 	/* This is root if it has v4l2_dev. */
-	if (!notifier->v4l2_dev)
+	if (!notifier->v4l2_dev) {
+		if (notifier->sd)
+			deb_dbg(notifier->sd->dev,
+				"V4L2 device not available\n");
 		return 0;
+	}
 
 	/* Is everything ready? */
 	if (!v4l2_async_nf_can_complete(notifier))
 		return 0;
 
+	deb_dbg(notifier->sd->dev, "complete\n");
+
 	return v4l2_async_nf_call_complete(notifier);
 }
 
@@ -386,6 +414,9 @@ v4l2_async_nf_try_all_subdevs(struct v4l2_async_notifier *notifier)
 			continue;
 
 		ret = v4l2_async_match_notify(notifier, v4l2_dev, sd, asd);
+		deb_dbg(sd->dev, "bound to %s's notifier (ret %d)\n",
+			notifier->sd ? dev_name(notifier->sd->dev) : "no-dev",
+			ret);
 		if (ret < 0)
 			return ret;
 
-- 
2.30.2