media: v4l2-async: Add waiting subdevices debugfs

There is currently little to no information available about the reasons
why a v4l2-async device hasn't probed completely.

Inspired by the "devices_deferred" debugfs file, add a file to list
information about the subdevices that are on waiting lists, for each
notifier.

This is useful to debug v4l2-async subdevices and notifiers, for instance
when doing device bring-up.

For instance, a typical output would be:

$ cat /sys/kernel/debug/video4linux/pending_async_subdevices
ipu1_csi1:
 [fwnode] dev=20e0000.iomuxc-gpr:ipu1_csi1_mux, node=/soc/bus@2000000/iomuxc-gpr@20e0000/ipu1_csi1_mux
ipu1_csi0:
 [fwnode] dev=20e0000.iomuxc-gpr:ipu1_csi0_mux, node=/soc/bus@2000000/iomuxc-gpr@20e0000/ipu1_csi0_mux
imx6-mipi-csi2:
 [fwnode] dev=1-003c, node=/soc/bus@2100000/i2c@21a4000/camera@3c
imx-media:

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-async.c

@@ -5,6 +5,7 @@
  * Copyright (C) 2012-2013, Guennadi Liakhovetski <g.liakhovetski@gmx.de>
  */
 
+#include <linux/debugfs.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
@@ -14,6 +15,7 @@
 #include <linux/mutex.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 
@@ -831,3 +833,67 @@ void v4l2_async_unregister_subdev(struct v4l2_subdev *sd)
 	mutex_unlock(&list_lock);
 }
 EXPORT_SYMBOL(v4l2_async_unregister_subdev);
+
+static void print_waiting_subdev(struct seq_file *s,
+				 struct v4l2_async_subdev *asd)
+{
+	switch (asd->match_type) {
+	case V4L2_ASYNC_MATCH_DEVNAME:
+		seq_printf(s, " [devname] dev=%s\n", asd->match.device_name);
+		break;
+	case V4L2_ASYNC_MATCH_I2C:
+		seq_printf(s, " [i2c] dev=%d-%04x\n", asd->match.i2c.adapter_id,
+			   asd->match.i2c.address);
+		break;
+	case V4L2_ASYNC_MATCH_FWNODE: {
+		struct fwnode_handle *devnode, *fwnode = asd->match.fwnode;
+
+		devnode = fwnode_graph_is_endpoint(fwnode) ?
+			  fwnode_graph_get_port_parent(fwnode) :
+			  fwnode_handle_get(fwnode);
+
+		seq_printf(s, " [fwnode] dev=%s, node=%pfw\n",
+			   devnode->dev ? dev_name(devnode->dev) : "nil",
+			   fwnode);
+
+		fwnode_handle_put(devnode);
+		break;
+	}
+	}
+}
+
+static const char *
+v4l2_async_notifier_name(struct v4l2_async_notifier *notifier)
+{
+	if (notifier->v4l2_dev)
+		return notifier->v4l2_dev->name;
+	else if (notifier->sd)
+		return notifier->sd->name;
+	else
+		return "nil";
+}
+
+static int pending_subdevs_show(struct seq_file *s, void *data)
+{
+	struct v4l2_async_notifier *notif;
+	struct v4l2_async_subdev *asd;
+
+	mutex_lock(&list_lock);
+
+	list_for_each_entry(notif, &notifier_list, list) {
+		seq_printf(s, "%s:\n", v4l2_async_notifier_name(notif));
+		list_for_each_entry(asd, &notif->waiting, list)
+			print_waiting_subdev(s, asd);
+	}
+
+	mutex_unlock(&list_lock);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(pending_subdevs);
+
+void v4l2_async_debug_init(struct dentry *debugfs_dir)
+{
+	debugfs_create_file("pending_async_subdevices", 0444, debugfs_dir, NULL,
+			    &pending_subdevs_fops);
+}

drivers/media/v4l2-core/v4l2-dev.c

@@ -14,6 +14,7 @@
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/debugfs.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
@@ -38,6 +39,7 @@
 		       __func__, ##arg);				\
 } while (0)
 
+static struct dentry *v4l2_debugfs_dir;
 
 /*
  *	sysfs stuff
@@ -1118,6 +1120,8 @@ static int __init videodev_init(void)
 		return -EIO;
 	}
 
+	v4l2_debugfs_dir = debugfs_create_dir("video4linux", NULL);
+	v4l2_async_debug_init(v4l2_debugfs_dir);
 	return 0;
 }
 
@@ -1125,6 +1129,7 @@ static void __exit videodev_exit(void)
 {
 	dev_t dev = MKDEV(VIDEO_MAJOR, 0);
 
+	debugfs_remove_recursive(v4l2_debugfs_dir);
 	class_unregister(&video_class);
 	unregister_chrdev_region(dev, VIDEO_NUM_DEVICES);
 }

include/media/v4l2-async.h

@@ -11,6 +11,7 @@
 #include <linux/list.h>
 #include <linux/mutex.h>
 
+struct dentry;
 struct device;
 struct device_node;
 struct v4l2_device;
@@ -120,6 +121,13 @@ struct v4l2_async_notifier {
 	struct list_head list;
 };
 
+/**
+ * v4l2_async_debug_init - Initialize debugging tools.
+ *
+ * @debugfs_dir: pointer to the parent debugfs &struct dentry
+ */
+void v4l2_async_debug_init(struct dentry *debugfs_dir);
+
 /**
  * v4l2_async_notifier_init - Initialize a notifier.
  *