v4l2h264enc doesn't support h264_i_frame_period=1 and h264_v4l2m2m doesn't respect -g parameter

When setting h264_i_frame_period=1, Gstreamer hangs at 1% using the following command:

gst-launch-1.0 -vvv videotestsrc pattern=snow num-buffers=100 ! video/x-raw,width=1920,height=1080,framerate=30/1 ! v4l2h264enc extra-controls="controls,video_bitrate_mode=0,video_bitrate=25000000,h264_i_frame_period=1,repeat_sequence_header=1" \
! 'video/x-h264,profile=high,level=(string)4.1' ! h264parse ! mp4mux ! filesink location=~/out.mp4 

But when h264_i_frame_period=2, it encodes correctly (frame types verified with ffprobe):

gst-launch-1.0 -vvv videotestsrc pattern=snow num-buffers=100 ! video/x-raw,width=1920,height=1080,framerate=30/1 ! v4l2h264enc extra-controls="controls,video_bitrate_mode=0,video_bitrate=25000000,h264_i_frame_period=2,repeat_sequence_header=1" \
! 'video/x-h264,profile=high,level=(string)4.1' ! h264parse ! mp4mux ! filesink location=~/out.mp4 

I'm unable to test FFmpeg's h264_v4l2m2m encoder's support of a keyframe interval = 1 as it doesn't respect the '-g' flag. FFmpeg throws this warning regardless of the '-g' flag:

[h264_v4l2m2m @ 0x55bef349d0] Failed to set gop size: Invalid argument

FFmpeg's issue could be potentially related to - https://trac.ffmpeg.org/ticket/2305

I am testing on a Compute Module 4 + Official IO Board + Bullseye Lite 64bit + 5.10.63-v8+ Kernel. Full system info here - https://pastebin.com/654vBepL

Let me know if you need any further info or help replicating.

Start by reproducing the provided gst-launch-1.0 case at h264_i_frame_period=1 and compare it with the working value of 2. Then investigate the v4l2h264enc and h264_v4l2m2m entry points and the reported GOP-setting warning. Done means the GStreamer case no longer hangs and FFmpeg's -g parameter is respected, with regression coverage where the relevant tests exist.