bcm2385-codec not reporting about encoder dropping frame

[lmkq222]

Describe the bug

While implementing v4l2 h264 encoding I have stumbled upon an issue of H264 encoder dropping frames when bitrate overshots intended values. According to Stateful-M2M-Encoder docs I expected to receive CAPTURE buffer with V4L2_BUF_FLAG_ERROR set, but looking at the bcm2385-codec it seems like it silently returns a buffer to the VPU without notifying user space.

Steps to reproduce the behaviour

1. Open V4L2 /dev/video11 encoder
2. Setup H264 encoding 720x576p, 25fps, bitrate 10MBit/s, constrained baseline profile, repeate sequence header
3. Open /dev/urandom and feed random data to the encoder
4. Observe encoder dropping frames and not notifying the user space

Device (s)

Raspberry Pi Zero 2 W

System

• Raspberry Pi reference 2025-02-05 Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 9a4a00f082b23c94caa210e7441fdf5d6a341056, stage2
• Nov 26 2024 12:54:19
  Copyright (c) 2012 Broadcom
  version 2ae30f53898ae2f1ba77ff570a92991bedfb0398 (clean) (release) (start)
• Linux raspberrypi 6.6.74+rpt-rpi-v8 1 SMP PREEMPT Debian 1:6.6.74-1+rpt1 (2025-01-27) aarch64 GNU/Linux

Logs

No response

Additional context

No response

[6by9]

Forum thread (such as it was) https://forums.raspberrypi.com/viewtopic.php?t=384108