wcn6855 2.1 - slow download speed on any pairwise cipher except CCMP

[Yaroslav Isakov]

Hello! When I tried to switch my OpenWRT router from default CCMP
pairwise cipher to any other, supported by both my router (Asus
TUF-AX6000) and my laptop (Thinkpat T14 Gen 4 AMD with WCN6855 2.1), I
saw that download dropped from 1Gbit/s to 100 MBit/s. When I changed
back to CCMP, download speed recovered back to 1Gbit/s. Upload speed
is good, though, for all ciphers - 1Gbit/s.

Initially, I thought, that issue with either router hardware, or
openwrt driver - but, I tested the same settings on another laptop -
T14 Gen3 Intel - and with Intel WIFI, both download and upload speed
was 1Gbit/s on any pairwise cipher.

This issue is 100% reproducible for me, it happens all the times I'm
switching to any pairwise cipher other than CCMP.

I'm on Linux 6.7.6, compiled from sources on Gentoo.

Here is my dmesg for ath11k:
[   13.092519] ath11k_pci 0000:02:00.0: BAR 0: assigned [mem
0x78600000-0x787fffff 64bit]
[   13.093400] ath11k_pci 0000:02:00.0: enabling device (0000 -> 0002)
[   13.095723] ath11k_pci 0000:02:00.0: MSI vectors: 32
[   13.096260] ath11k_pci 0000:02:00.0: wcn6855 hw2.1
[   13.974707] ath11k_pci 0000:02:00.0: chip_id 0x12 chip_family 0xb
board_id 0xff soc_id 0x400c1211
[   13.974732] ath11k_pci 0000:02:00.0: fw_version 0x1106196e
fw_build_timestamp 2024-01-12 11:30 fw_build_id
WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.37
[   14.315774] ath11k_pci 0000:02:00.0: Failed to set the requested
Country regulatory setting
[   14.316046] ath11k_pci 0000:02:00.0: Failed to set the requested
Country regulatory setting
[  337.889222] ath11k_pci 0000:02:00.0: failed to enqueue rx buf: -28