arducam-pivariety: missing V4L2_CID_LINK_FREQ causes DPHY "Datarate out of range" on Pi 5 (RP1)

Start in arducam-pivariety.c, especially pivariety_parse_dt() and pivariety_enum_controls(), and inspect how v4l2_fwnode_endpoint_alloc_parse() and v4l2_fwnode_endpoint_free() handle the endpoint data. Reproduce with rpicam-hello on a Raspberry Pi 5 while watching journalctl -f. Done means the 496 MHz device-tree link frequency is exposed to V4L2 and the RP1 log no longer reports a 1920 Mbps rate or an out-of-range DPHY datarate.

Describe the bug

The arducam-pivariety.c driver does not implement V4L2_CID_LINK_FREQ.
When libcamera opens the camera, v4l2_get_link_freq() finds no control,
falls back to estimating from pixel rate, and arrives at 1920 Mbps (even though I am not using over 14Mbps). The
RP1 DPHY only supports 80–1500 Mbps, so it is programmed at the wrong
rate, causing unstable frame delivery and periodic multi-second frame gaps.

The correct link frequency (496 MHz) is already present in the device tree
overlay (arducam-pivariety.dtbo) but pivariety_parse_dt() discards it after
parsing — ep_cfg.link_frequencies[0] is never saved or exposed as a V4L2
control.

Additional context includes my working theory — happy to hear if others have seen the same or can confirm the root cause.

Steps to reproduce the behaviour

1. Attach an Arducam Pivariety camera to Raspberry Pi 5
2. Load the overlay: dtoverlay=arducam-pivariety in /boot/firmware/config.txt
3. Open the camera with any libcamera app:
   4. rpicam-hello --camera 0
4. Observe kernel log:
   journalctl -f

Device (s)

Raspberry Pi 5

System

https://paste.debian.net/hidden/25cb6979

Logs

Apr 09 16:00:29 raspberrypi kernel: v4l2_get_link_freq: Link frequency estimated using pixel rate: result might be inaccurate
Apr 09 16:00:29 raspberrypi kernel: v4l2_get_link_freq: Consider implementing support for V4L2_CID_LINK_FREQ in the transmitter driver
Apr 09 16:00:29 raspberrypi kernel: rp1-cfe 1f00110000.csi: Using a link rate of 1920 Mbps
Apr 09 16:00:29 raspberrypi kernel: rp1-cfe 1f00110000.csi: DPHY: Datarate 1920 Mbps out of range
Apr 09 16:00:31 raspberrypi kernel: v4l2_get_link_freq: Link frequency estimated using pixel rate: result might be inaccurate
Apr 09 16:00:31 raspberrypi kernel: v4l2_get_link_freq: Consider implementing support for V4L2_CID_LINK_FREQ in the transmitter driver
Apr 09 16:00:31 raspberrypi kernel: rp1-cfe 1f00128000.csi: Using a link rate of 1920 Mbps
Apr 09 16:00:31 raspberrypi kernel: rp1-cfe 1f00128000.csi: DPHY: Datarate 1920 Mbps out of range

Additional context

From looking at the driver:
It appears in pivariety_parse_dt() (arducam-pivariety.c):
v4l2_fwnode_endpoint_alloc_parse() correctly populates
ep_cfg.link_frequencies[0] = 496000000 from the DT overlay, but
v4l2_fwnode_endpoint_free() is called immediately after without
saving the value. V4L2_CID_LINK_FREQ is never registered in
pivariety_enum_controls() either.