[v4] 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>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
---
 drivers/media/v4l2-core/v4l2-async.c | 63 ++++++++++++++++++++++++++++
 drivers/media/v4l2-core/v4l2-dev.c   |  5 +++
 include/media/v4l2-async.h           |  8 ++++
 3 files changed, 76 insertions(+)

Hi Ezequiel,

On 15/01/2021 19:14, Ezequiel Garcia wrote:
> 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:

Oh this is very exciting. I started looking at something like this
recently, hitting async failures, and this already looks better.

In other words, - Thank you!

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> ---
>  drivers/media/v4l2-core/v4l2-async.c | 63 ++++++++++++++++++++++++++++
>  drivers/media/v4l2-core/v4l2-dev.c   |  5 +++
>  include/media/v4l2-async.h           |  8 ++++
>  3 files changed, 76 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> index e3ab003a6c85..e35f18706792 100644
> --- a/drivers/media/v4l2-core/v4l2-async.c
> +++ b/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>
>  
> @@ -837,3 +839,64 @@ 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_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);
> +}
> 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);
>  }
> diff --git a/include/media/v4l2-async.h b/include/media/v4l2-async.h
> index 0e04b5b2ebb0..243ac10a53c6 100644
> --- a/include/media/v4l2-async.h
> +++ b/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;
> @@ -137,6 +138,13 @@ 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.
>   *
>