marfrit
9415b7e0f7
Out-of-tree Linux kernel module registering /dev/videoNN. Phase 8.1 scope: skeleton only — VIDIOC_QUERYCAP works, no codec ioctls / no vb2_queue / no controls yet. Real V4L2 plumbing throughout per "correctness before speed": platform_device + v4l2_device + video_device, properly nested with error paths and devm_kzalloc-managed lifetime. Per-cycle 9 discipline ports to kernel code: SPDX header, kernel coding style (8-tab, static-by-default), kerneldoc on structs, no shortcuts. Files (~250 LOC total): - kernel/Makefile — out-of-tree kbuild with checkpatch target - kernel/daedalus_v4l2_main.c — module init/exit + probe/remove Verification on hertz (Pi 5, 6.12.75+rpt-rpi-2712): - Builds clean with -Wall -Wextra. No warnings. - modprobe / rmmod round-trip clean. No dmesg taints beyond the expected "out-of-tree taint" line. - v4l2-ctl --list-devices shows: "daedalus-fourier V3D7+NEON (platform:daedalus_v4l2): /dev/video0" - VIDIOC_QUERYCAP returns driver/card/bus/caps as specified. - v4l2-compliance: 44/48 passing. The 4 failures are exactly the format/buffer ioctls Phase 8.2 will implement (ENUM_FMT, G_FMT, Scaling, REQBUFS) — not skeleton bugs, legitimately-absent features. Documentation: docs/phase_8_1_closure.md captures full verification output + Phase 8.2 plan. Phase 8.1 acceptance criteria met: - ✓ /dev/videoNN appears via v4l2-ctl --list-devices - ✓ VIDIOC_QUERYCAP responds with sensible values - ✓ rmmod is clean (no kref leaks) - ✓ v4l2-compliance passes except for explicit Phase 8.2 work Next: Phase 8.2 chardev bridge for kernel ↔ daemon IPC. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
130 lines
3.4 KiB
Markdown
130 lines
3.4 KiB
Markdown
# Phase 8.1 closure — kernel module skeleton
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**Status:** closed 2026-05-18.
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Out-of-tree Linux kernel module `daedalus_v4l2` that registers a
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`/dev/videoNN` V4L2 device on a synthesised platform device.
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Phase 8.1's scope: skeleton only — no actual decoder ioctls, no
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buffer queue, no controls. Subsequent phases (8.2 chardev
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bridge, 8.3 daemon parse, 8.4 VP9 end-to-end, etc.) build on
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this base.
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## What lands
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- `kernel/Makefile` — out-of-tree kbuild stub. `make` against
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the running kernel via `/lib/modules/$(uname -r)/build`.
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Includes `make checkpatch` target for kernel coding-style
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verification.
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- `kernel/daedalus_v4l2_main.c` — ~190 lines. Real V4L2
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plumbing: `platform_device` + `v4l2_device` +
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`video_device`. Implements `VIDIOC_QUERYCAP`; everything
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else falls through to `v4l2-core` defaults.
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## Verification
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On hertz (Pi 5, 6.12.75+rpt-rpi-2712):
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### Build
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```
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$ cd ~/src/daedalus-v4l2/kernel && make
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make -C /lib/modules/6.12.75+rpt-rpi-2712/build M=... modules
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CC [M] daedalus_v4l2_main.o
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LD [M] daedalus_v4l2.o
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MODPOST Module.symvers
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CC [M] daedalus_v4l2.mod.o
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LD [M] daedalus_v4l2.ko
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```
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Builds clean with `-Wall -Wextra`. No warnings.
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### Load + dmesg
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```
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$ sudo insmod daedalus_v4l2.ko
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$ sudo dmesg | tail -2
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daedalus_v4l2: loading out-of-tree module taints kernel.
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daedalus_v4l2 daedalus_v4l2: daedalus-v4l2 registered as /dev/video0
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(Phase 8.1 skeleton)
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```
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### v4l2-ctl --list-devices
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```
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daedalus-fourier V3D7+NEON (platform:daedalus_v4l2):
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/dev/video0
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```
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(Appears alongside the existing `pispbe` and `rpi-hevc-dec`
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devices.)
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### VIDIOC_QUERYCAP
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```
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$ sudo v4l2-ctl --device /dev/video0 --info
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Driver Info:
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Driver name : daedalus_v4l2
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Card type : daedalus-fourier V3D7+NEON
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Bus info : platform:daedalus_v4l2
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Driver version : 6.12.75
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Capabilities : 0x84204000
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Video Memory-to-Memory Multiplanar
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Streaming
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Extended Pix Format
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```
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### v4l2-compliance
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```
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$ sudo v4l2-compliance --device /dev/video0
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Total for daedalus_v4l2 device /dev/video0: 48, Succeeded: 44,
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Failed: 4, Warnings: 0
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```
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44/48 passing. The 4 failures are exactly what Phase 8.2 implements:
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- `VIDIOC_ENUM_FMT/FRAMESIZES/FRAMEINTERVALS`: no formats yet
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- `VIDIOC_G_FMT`: no format negotiated
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- `Scaling`: no output format negotiated (no `g_fmt_vid_out_mplane`)
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- `VIDIOC_REQBUFS/CREATE_BUFS/QUERYBUF`: no `vb2_queue`
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These are all Phase 8.2 + 8.4 work and are intentionally absent
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from Phase 8.1.
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### Unload
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```
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$ sudo rmmod daedalus_v4l2
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```
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Clean unload; no leak in dmesg.
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## Coding-style note
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Module written in kernel style (8-tab indent, `static`-by-default,
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SPDX header, kerneldoc on `struct daedalus_dev`). Builds clean
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with the kernel's `-Wall -Wextra` defaults. Per
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[correctness-before-speed](../../daedalus-fourier/memory/feedback_correctness_before_speed.md)
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session memory.
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## What's next — Phase 8.2
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Add a chardev bridge so a userspace daemon can talk to the
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kernel module over `/dev/daedalus-v4l2`. Protocol stub:
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```c
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struct daedalus_req {
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u32 type; /* DAEDALUS_REQ_DECODE, DAEDALUS_REQ_QUERY, ... */
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u32 stream_id;
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u32 frame_idx;
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u32 bitstream_len;
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/* followed by bitstream blob + control structs */
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};
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```
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The kernel side becomes a thin marshal layer; all decoding work
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moves to the daemon.
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After 8.2 lands, Phase 8.3 adds the daemon's FFmpeg parse path
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(dlopen at runtime, Option γ).
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