Real H.264 access units routinely exceed the previous 64 KiB cap
on the chardev wire protocol:
720p worst-case I-frame ~200 KiB
1080p worst-case I-frame ~500 KiB
libva-v4l2-request-fourier detects the under-sized OUTPUT-MPLANE
buffer and tries to grow it via VIDIOC_S_FMT to 147456 B, but
daedalus_fill_output_fmt unconditionally pins sizeimage to
DAEDALUS_MAX_BITSTREAM (= 65484) regardless of userspace's
request. Firefox loses the slice, falls back to libmozavcodec
SW for the rest of the session.
Bumping the wire-protocol cap to 1 MiB lifts the kernel
OUTPUT_MPLANE sizeimage with it (DAEDALUS_MAX_BITSTREAM is derived
from the same #define). All allocations (kernel kmalloc /
kmemdup, daemon read buffer, vb2 plane backing) are dynamic and
sized per-payload at runtime, so the only growth is the daemon's
startup read buffer (one ~1 MiB allocation per daemon process)
and the V4L2 OUTPUT_MPLANE per-buffer size. KMALLOC_MAX_SIZE on
aarch64 SLUB is several MiB; 1 MiB is well within bounds. Other
V4L2 stateless decoders (cedrus, rkvdec, hantro) report 1-4 MiB
OUTPUT_MPLANE sizeimage — this puts daedalus at the conservative
end of normal.
## Compatibility
#define-only change; struct layout unchanged. But the
effective cap is the smaller of (kernel cap, daemon cap), so:
- new daemon + stale kernel: still capped at 64 KiB until the
kernel module rebuilds.
- new kernel + stale daemon: same.
Lock-step install of daedalus-v4l2 + daedalus-v4l2-dkms is
therefore required for the fix to take effect; mirrors the
PR-#7/#8 cadence.
## NOT changed in this commit
- daedalus_fill_output_fmt still hardcodes sizeimage =
DAEDALUS_MAX_BITSTREAM regardless of userspace request.
Acceptable: vb2 will allocate up to that, and libva's resize-
test now sees the kernel report a sizeimage at-least-as-large
as what it asked for (147456 < 1048524). A future cleanup
could respect userspace's S_FMT.sizeimage clamped to the cap,
to save memory on tiny streams.
- chardev kmalloc → kvmalloc swap (only matters above
KMALLOC_MAX_SIZE, not here).
Refs #19.
marfrit
ee42419479