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>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/media/v4l2-core/v4l2-dev.c b/drivers/media/v4l2-core/v4l2-dev.c
index f9cff033d0dc..b6a72d297775 100644
--- a/drivers/media/v4l2-core/v4l2-dev.c
+++ b/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);
 }