Re: [BUG] rtw88 8821ce: connection wedges (100% loss until reboot) with station power save

[Abdurrahman Karadag <abdurrahmankaradag19@gmail.com>]

Correction and new data.

First, a correction to my report: I have now hit the wedge with station
power save OFF, so power save is not the trigger. My earlier "power_save
off makes it stop" was coincidence on an intermittent bug. Please disregard
the PS/smart_ps angle.

Second, I captured a wedge with Wireshark on wlan0 (802.3 view, i.e. at the
netdev boundary), and the signature is much more specific than "connection
wedges":

  - RX is fully intact, including unicast: DHCP OFFER/ACK addressed to my
    MAC, an ICMP echo request from the router, TLS data from the router,
    and the gateway's ARP requests sent *unicast* to me were all received.
  - My DHCP DISCOVER/REQUEST (342/345 bytes, L2 broadcast) reach the AP and
    are answered within milliseconds - on two different APs (an Android
    hotspot and a MikroTik router).
  - 14-30 ms after those successful DHCP exchanges, my ARP requests for the
    gateway (42 bytes, L2 broadcast; 89 of them, 1/s) get zero replies on
    both networks.
  - The gateway ARPs *me* (unicast, 10 times at ~0.77 s intervals, then
    falls back to broadcast). I receive every request and reply immediately
    (42-byte unicast ARP reply) - yet it keeps asking, so my replies never
    reach it.
  - My TCP SYNs (78 bytes, unicast to the gateway MAC) get no SYN-ACK.

So the failing set is small STA->AP frames (42-byte ARP, both broadcast
and unicast; 78-byte SYN) and the working set is 342-byte broadcast DHCP,
with RX working throughout and no kernel/driver messages. Since DHCP
succeeds tens of milliseconds before ARP fails, this looks like a
per-frame property (frame size, or possibly ethertype) rather than a
temporal stall. Two unrelated APs show the identical pattern, so it is
not AP-specific. The interface stays associated; only a reboot clears it
(a live driver reload froze the machine once, so I avoid that).

Next time it wedges I will run a size probe (static ARP entry for the
gateway, then ping -s 8/56/200/400/1000) to confirm whether it is
size-dependent, plus station-dump tx-failed/retry deltas and a
neigh-flush -> reconnect -> link down/up ladder to see which layer holds
the wedge. If there is anything specific on the 8821c TX side you would
like me to dump (tx desc, debugfs, registers) while it is wedged, tell me
and I will capture it.

Capture available on request.