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marfrit c7d8050cc9 Initial scaffold: daedalus-v4l2 sibling repo

V4L2 stateless decoder for Pi 5, backed by sibling
daedalus-fourier kernel library (VP9 + AV1 CDEF + H.264 video
decode kernels on VideoCore VII compute + ARM NEON).

Architecture locked 2026-05-18 by mfritsche per
daedalus-fourier/docs/phase8_scoping.md:
- Option B: Linux kernel V4L2 shim + userspace daemon (not
  v4l2loopback). Real /dev/videoNN; proper DRM PRIME for
  browser zero-copy.
- Option γ: dlopen FFmpeg at runtime as parser. No vendoring;
  fastest to v1.
- Sibling repo (this repo): V4L2-side work outside of
  daedalus-fourier so kernel-library API stays clean.

Components:
  kernel/ - Linux out-of-tree kernel module (GPLv2; V4L2
    device + chardev bridge to userspace daemon)
  daemon/ - userspace decoder daemon (BSD-2-Clause; links
    libdaedalus_core.a from sibling; dlopens FFmpeg)
  docs/   - architecture + 7-phase roadmap (8.1..8.7)
  include/ - shared headers between kernel and daemon

Roadmap (7 sub-phases, ~1 week each):
  8.1 kernel skeleton (/dev/videoNN with no-op ioctls)
  8.2 chardev bridge (kernel ↔ daemon ping-pong)
  8.3 daemon FFmpeg dlopen + parse path
  8.4 VP9 end-to-end via daedalus_dispatch_*
  8.5 dmabuf / DRM PRIME for zero-copy
  8.6 AV1 + H.264 codec support
  8.7 performance: hit 30fps@1080p (project floor)

No code yet — only README + design docs + directory structure.
First implementation work starts in Phase 8.1 next session.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-18 14:54:56 +00:00

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daedalus-v4l2

V4L2 stateless decoder for the Raspberry Pi 5 / CM5, backed by the daedalus-fourier kernel library (VP9 + AV1 CDEF + H.264 video decode kernels on VideoCore VII compute + ARM NEON).

Status: scaffold (2026-05-18). Architecture locked per daedalus-fourier session memory; implementation not yet begun.

What this is

A two-piece userspace + kernel-module stack that exposes a V4L2 stateless decoder interface (/dev/videoNN) so that libva-v4l2-request-fourier → firefox-fourier / chromium-fourier can drive it the same way they drive existing hardware-decode pipelines on Pi 5 / RK3588.

+-----------------------------------------------------------+
| firefox-fourier / chromium-fourier  (existing)            |
+-----------------------------------------------------------+
| VA-API                                                    |
+-----------------------------------------------------------+
| libva-v4l2-request-fourier  (existing, sibling project)   |
+-----------------------------------------------------------+
| V4L2 stateless ioctl uAPI                                 |
+-----------------------------------------------------------+
| daedalus-v4l2 kernel module  (`kernel/`)                  |
|   - registers /dev/videoNN                                |
|   - parses V4L2 stateless ioctls (VP9/AV1/H.264 controls) |
|   - forwards bitstream + controls to userspace daemon     |
|     via chardev or netlink                                |
+-----------------------------------------------------------+
| daedalus-v4l2 userspace daemon  (`daemon/`)               |
|   - takes bitstream blobs + per-slice controls            |
|   - drives FFmpeg parsers via dlopen (Option γ)           |
|   - dispatches per-block ops via daedalus-fourier         |
|     public API (daedalus_dispatch_*)                      |
|   - posts decoded frames back to kernel module            |
+-----------------------------------------------------------+
| daedalus-fourier kernel library  (sibling project)        |
|   - exports include/daedalus.h public API                 |
|   - per-kernel CPU NEON + opportunistic V3D QPU dispatch  |
|   - 9 closed cycles across VP9, AV1 CDEF, H.264           |
+-----------------------------------------------------------+
| V3D 7.1 (Mesa userspace v3dv) + ARM NEON (BCM2712)        |
+-----------------------------------------------------------+

Why this architecture (Option B + γ + sibling)

Locked by user 2026-05-18 from 3 options in daedalus-fourier/docs/phase8_scoping.md:

Option B over A (userspace v4l2loopback): real /dev/videoNN, proper DRM PRIME / dmabuf for browser zero-copy.
Option γ: dlopen FFmpeg as parser at runtime. No vendoring, fastest to v1.
Sibling repo: per project_consumer_target convention, V4L2-side work lives outside daedalus-fourier so the kernel-library has a clean API boundary.

Status

Initial scaffold only. See docs/architecture.md for the deeper design and docs/roadmap.md for the sub-phase breakdown.

Repo layout

kernel/ — Linux kernel module (V4L2 device registration + ioctl handling + userspace chardev bridge). Out-of-tree.
daemon/ — userspace decoder daemon (links libdaedalus_core.a from sibling daedalus-fourier; uses dlopen for FFmpeg parser).
include/ — shared headers between kernel and daemon.
docs/ — architecture + roadmap.

License

Kernel module: GPLv2 (required for kernel-tree compatibility). Userspace daemon: BSD-2-Clause (matches daedalus-fourier).

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