rp1-cfe doesn't forward V4L2_EVENT_SOURCE_CHANGE event from csi-2 sensor driver to userspace app

[hryhoriitur]

Describe the bug

Currently, I am developing driver for csi-2 camera, and noticed that when I execute v4l2_subdev_notify_event in my driver, it is not being received by my userspace application.
What I do:

memset(&ev, 0, sizeof(ev));
ev.type = V4L2_EVENT_SOURCE_CHANGE;
ev.u.src_change.changes = V4L2_EVENT_SRC_CH_RESOLUTION;
v4l2_subdev_notify_event(my_subdev, &ev);

After a quick debugging I found the reason in rp1-cfe driver. It looks that the check whether the node in NODE_REGISTERED state in function cfe_notify is incorrect:

case V4L2_DEVICE_NOTIFY_EVENT:
for (i = 0; i < NUM_NODES; i++) {
struct cfe_node *node = &cfe->node[i];

  	if (check_state(cfe, NODE_REGISTERED, i))
  		continue;

  	v4l2_event_queue(&node->video_dev, arg);

According to this code, the event will be sent only if the corresponding cfe node is not in NODE_REGISTERED state..
The fix is trivial:

if (!check_state(cfe, NODE_REGISTERED, i))

Steps to reproduce the behaviour

1. Start listening for V4L2_EVENT_SOURCE_CHANGE event using v4l2-ctl:
   v4l2-ctl -d /dev/video0 --all --verbose --wait-for-event=source_change
2. Try to send event from csi-2 sensor driver using v4l2_subdev_notify_event
3. v4l2-ctl doesn't receive corresponding event

Device (s)

Raspberry Pi 5

System

raspinfo | head -n 17
System Information
Raspberry Pi 5 Model B Rev 1.0
PRETTY_NAME="Debian GNU/Linux 13 (trixie)"
NAME="Debian GNU/Linux"
VERSION_ID="13"
VERSION="13 (trixie)"

Raspberry Pi reference 2025-12-04
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 4997bf4e4e49bc3305eb182a4a08bd023529da04, stage4

Linux raspberrypi 6.12.47+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.47-1+rpt1 (2025-09-16) aarch64 GNU/Linux
Revision : d04170
Serial : 7c04ad32b8996900
Model : Raspberry Pi 5 Model B Rev 1.0
Throttled flag : throttled=0x0

vcgencmd version
2025/11/05 17:37:18
Copyright (c) 2012 Broadcom
version 57db150d (release) (embedded)

Logs

No response

Additional context

No response

[6by9]

It's not clear to me whether this is the correct behaviour or not in a device configured through Media Controller rather than being video-node centric.

The CFE isn't the source subdev that will be generating a V4L2_EVENT_SOURCE_CHANGE event.
Trying to call v4l2_subdev_notify_event with presumably the fd for /dev/video0 would therefore appear to be wrong, and I would have expected you to be using the /dev/v4l-subdevN for your source subdev. I'm fairly certain that is how others using the Toshiba TC358743 on Pi5 have architected it.

It is mentioned in https://docs.kernel.org/driver-api/media/v4l2-subdev.html#calling-subdev-operations, but that section is also referencing calling the g_std subdev op, which is not something that should be done when using Media Controller. Reading the cfe_notify handler, it seems wrong that ALL /dev/video nodes of the CFE should notify the event as that sounds like it'll give multiple handling. Comparing to Renesas rvin's driver, that is matching against the subdev, but I'd need to check how many /dev/video devices it creates and whether it is a 1:1 mapping or not.

Registering for events from subdevs is covered in https://docs.kernel.org/driver-api/media/v4l2-subdev.html#v4l2-sub-device-userspace-api