besser/notes/observed-bugs.md

# Observed BES2600 driver bugs on PineTab2 (ohm)

Compiled from on-device dmesg + Pine64 wiki + community reports. Cross-references the patch series.

## Bug #1 — factory.txt path mismatch + filp_open antipattern (FIXED in c1)

**File**: `bes2600_factory.c:148-170` (read), `:188-200` (create)

**Symptom (pre-fix)**:
```
(NULL device *): read and check /lib/firmware/bes2600_factory.txt error
```

**Root cause**: hardcoded `FACTORY_PATH=/lib/firmware/bes2600_factory.txt` Makefile macro;
real file ships at `/lib/firmware/bes2600/bes2600_factory.txt`. Worse, the read uses
`filp_open` + `kernel_read` directly, bypassing the firmware-class infrastructure.

**Fix**: c1 patch — `request_firmware()` for the read path, repointed Makefile macro
to firmware-class name `bes2600/bes2600_factory.txt`.

## Bug #1.5 — factory.txt parse failure (NEW, c5 to investigate)

**File**: `bes2600_factory.c factory_parse()`

**Symptom (post-c1)**:
```
bes2600_factory.txt parse fail
read and check bes2600/bes2600_factory.txt error
factory cali data get failed.
```

**How discovered**: c1 fix exposed a deeper bug — `factory_parse()` chokes on the data
that `request_firmware()` now successfully returns. The original bug masked this
because the read always failed first.

**Hypotheses**: null-termination assumption mismatch (`request_firmware` doesn't
null-terminate), `FACTORY_MEMBER_NUM=30/31` count discrepancy, kmalloc not
zero-initialized, parser strict on trailing `%%\n` delimiter.

**Status**: investigation pending (task c5). Driver falls back to defaults; WiFi
functional but TX power is uncalibrated (all channels at 0x1400).

## Bug #2 — PM low-power handshake timeout (recurring)

**File**: `bes_pwr.c:470-558` — `bes2600_pwr_enter_lp_mode()`. Error at line 538.

**Symptom**:
```
bes2600_wlan mmc2:0001:1: bes2600_pwr_enter_lp_mode, wait pm ind timeout
```

Fires every 5–10s in steady state when associated. Floods dmesg, likely
correlates with bug #3 (SDIO TX stack splat) and bad battery life.

**Root cause**: `wait_for_completion_timeout(&pm_enter_cmpl, 5*HZ)` waits
for firmware to acknowledge a PM mode change; firmware never sends ACK.
Driver proceeds to `bes2600_pwr_device_enter_lp_mode()` regardless.

**Mobian == danctnix**: identical bes_pwr.c (1447 lines, 0-hunk diff). No
upstream fix exists; we'd invent it (gate device-LP entry on completion +
add retry).

**Status**: task c2.

## Bug #3 — SDIO TX scatter-gather panic / WARN

**File**: `bes2600_sdio.c:952-1200` — `bes_sdio_memcpy_to_io_helper`,
`sdio_tx_work`.

**Symptom**:
```
[RX] Receive failure: 4.
 bes_sdio_memcpy_to_io_helper+0x18c/0x288 [bes2600]
 sdio_tx_work+0x2b4/0x4a0 [bes2600]
Workqueue: bes_sdio sdio_tx_work [bes2600]
```

Recurring under TX load. Can wedge the chip irrecoverably (per Pine64 wiki:
"Power/reset circuitry not properly implemented; hard reset impossible
without board power-cycle").

**Status**: task c3 (indirectly, via bes_chardev removal which currently
gates the signal/nosignal mode switch path).

## Architect review — now BUG-#5-blocking (was backlog)

The Phase 0 perf trace for Bug #5 first exposed a "when in doubt, add a
lock" pattern (~20 % CPU in `_raw_spin_unlock_irqrestore`). The
follow-up ftrace measurement (2026-05-07 17:00) refined the root cause
to an architectural problem: **the bes2600 driver dispatches every
SDIO transaction through the kernel workqueue**. Numbers from a 3-min
4 MB/s ohm capture (post-reboot, srcversion `1B3B3ED0`):

```
wsm_cmd_send:               13/sec    (host-to-chip command rate, surprisingly low)
bes2600_rx_cb:             611/sec
bes2600_bh_wakeup:         267/sec
lock contention_begin:      50/sec
workqueue_execute_start: 5,643/sec    ← DOMINATES; matches the mmc
                                       transaction rate from earlier perf
```

5.6 k workqueue dispatches per second is the throughput floor — not a
specific lock, not WSM-command rate, not decrypt-state. A surgical fix
to any single function won't move the floor; the architecture needs
to be restructured to amortise SDIO transactions across fewer work-
items (or move SDIO RX out of the workqueue entirely).

This is where the **Claude Sonnet architect review** belongs: a
top-to-bottom assessment of `~/src/besser/bes2600-dkms-mobian/bes2600/`
focused on:

- the workqueue dispatch shape (most actionable)
- needless lock proliferation (the original signal)
- BH / RX scheduling boundaries
- error-handling coverage and dead-code from the cw1200 ancestor
- API contract violations relative to mainline mac80211

Output: ranked list of restructuring targets, with predicted-delta
estimates against the Phase 1 metric (≥ 2 MB/s sustained @ 4 MB/s cap,
< 10 % CPU in lock-cycling, no link cascade in 30 min).

**Status**: now blocking on Bug #5 (was independent track). Surgical
patches B5-1, B5-2, B5-3 from the original Phase 4 candidate list are
all DEFERRED until the architect review's restructuring map is in.

## Bug #5 — RX path degrades under attempted-throughput pressure

**Suspect file**: bes2600 RX path (`txrx.c bes2600_rx_cb`, `bh.c bes2600_bh_work`,
SDIO RX scheduling) — pinpoint pending.

**Symptom (observed 2026-05-07 13:43, srcversion `1B3B3ED0` = c-stack +
Patch A + Patch B, ohm @ -57 dBm 2.4GHz ch11 5b:32, idle save for the
netcat load):**

```
sender cap 1 MB/s  →  ohm receives 1015 KB/s,  signal -57 dBm,  RX MCS 4
sender cap 4 MB/s  →  ohm receives  563 KB/s,  signal -67 dBm,  RX MCS 3
                     (Send-Q on boltzmann backed up to 1.16 MB)
```

Pushing the sender-side cap from 1 MB/s to 4 MB/s **decreased** observed
throughput at the receiver and degraded the link metrics. Signal dropped
~10 dB and the chip downshifted MCS, suggesting the chip can't sustain
the higher RX rate even with the link physically capable of more (link
bitrate 65 Mb/s = ~8 MB/s theoretical).

**Hypothesis (Markus, 2026-05-07): driver/firmware locks itself to death
under busy reads** — possibly a busy-wait loop or lock contention on the
RX SDIO path that prevents draining at line rate. Plausible reason it
didn't surface for the c-stack tasks: those operated at typical
browse-rate traffic, well below the saturation threshold this bug needs
to fire.

**May explain**: original Phase-0 observation that **YouTube DASH chunks
drop ~10 frames per chunk fetch** on hardware-decoder playback. A chunk
fetch is a brief burst at near-link-rate; if the driver throttles itself
down during high-RX, the player buffer underruns for the duration of
the fetch.

**How to drill (when prioritized)**:
- Capture trace_pipe with `mmc:*` and `sdio*` events enabled during a
  controlled rate-ramp (e.g., pv -L 500K, 1M, 2M, 4M each for 60 s).
- Watch `/proc/sys/kernel/sched_*` and the `bes2600_bh_work` kworker for
  CPU saturation.
- `perf top -p $(pgrep -f bes_sdio)` during 4 MB/s load.

**Status**: backlog. No patch yet.

## Bug #4 — scan_complete_cb constant loop

**File**: `scan.c:883-909` — `bes2600_scan_complete_cb()`.

**Symptom**:
```
ieee80211 phy0: bes2600_scan_complete_cb status: 0
```

Fires every 2–10s (status=0 = success, but the FREQUENCY suggests background
scanning runs continuously when associated + idle).

Most likely a NetworkManager scheduling artifact, not a driver bug. Low
priority; suppress the wiphy_dbg print or skip scan-on-assoc'd if it
matters.