MT7615D K2P with DBDC stuck at "link up"

Device Info: https://openwrt.org/toh/hwdata/phicomm/phicomm_k2p

WLAN Hardware: MediaTek MT7615D
WLAN 2.4GHz: b/g/n
WLAN 5.0GHz: a/n/ac

root@OpenWrt:/# dmesg | grep 7615
[    1.806137] pci 0000:01:00.0: [14c3:7615] type 00 class 0x000280

since changeset 99804560372bfb830de28a41ecc4736747c2ae60 we don't need echo 1 > /sys/kernel/debug/ieee80211/phy0/mt76/dbdc any more, but it's not enough for K2P MT7615D

ip a command (and all script to bring wlan up) freeze during/after a clean reboot
this is what happen after loading mt7615e module, with a few extra log added by me

[   14.406743] mt7621-pci 1e140000.pcie: bus=1 slot=0 irq=23
[   14.417549] pci 0000:00:00.0: enabling device (0004 -> 0007)
[   14.428838] mt7615e 0000:01:00.0: enabling device (0000 -> 0002)
[   14.463379] mt7615_register_device: has_2g=1 n_rates=12
[   14.819124] mt7615e 0000:01:00.0: HW/SW Version: 0x8a108a10, Build Time: 20180518100604a
[   14.819124] 
[   14.824876] NET: Registered protocol family 24
[   14.866768] kmodloader: done loading kernel modules from /etc/modules.d/*
[   15.389394] mt7615e 0000:01:00.0: N9 Firmware Version: _reserved_, Build Time: 20200814163649
[   15.448834] mt7615e 0000:01:00.0: CR4 Firmware Version: _reserved_, Build Time: 20190121161307
[   16.368333] zram0: detected capacity change from 0 to 61865984
[   21.002884] mtk_soc_eth 1e100000.ethernet eth0: Link is Down
[   21.031289] mtk_soc_eth 1e100000.ethernet eth0: configuring for fixed/rgmii link mode
[   21.047348] mtk_soc_eth 1e100000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[   21.067379] mtk_soc_eth 1e100000.ethernet eth0: Link is Down
[   21.228767] mtk_soc_eth 1e100000.ethernet eth0: configuring for fixed/rgmii link mode
[   21.244892] mtk_soc_eth 1e100000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[   21.248259] mt7530 mdio-bus:1f lan1: configuring for phy/gmii link mode
[   21.275728] 8021q: adding VLAN 0 to HW filter on device lan1
[   21.290667] br-wan: port 1(lan1) entered blocking state
[   21.301162] br-wan: port 1(lan1) entered disabled state
[   21.312526] device lan1 entered promiscuous mode
[   21.321792] device eth0 entered promiscuous mode
[   21.348247] mt7530 mdio-bus:1f lan2: configuring for phy/gmii link mode
[   21.362221] 8021q: adding VLAN 0 to HW filter on device lan2
[   21.377620] br-wan: port 2(lan2) entered blocking state
[   21.388201] br-wan: port 2(lan2) entered disabled state
[   21.400190] device lan2 entered promiscuous mode
[   21.418789] mt7530 mdio-bus:1f lan3: configuring for phy/gmii link mode
[   21.432652] 8021q: adding VLAN 0 to HW filter on device lan3
[   21.447444] br-wan: port 3(lan3) entered blocking state
[   21.458071] br-wan: port 3(lan3) entered disabled state
[   21.469990] device lan3 entered promiscuous mode
[   21.489244] mt7530 mdio-bus:1f lan4: configuring for phy/gmii link mode
[   21.503200] 8021q: adding VLAN 0 to HW filter on device lan4
[   21.517682] br-wan: port 4(lan4) entered blocking state
[   21.528245] br-wan: port 4(lan4) entered disabled state
[   21.540657] device lan4 entered promiscuous mode
[   21.556942] mt7530 mdio-bus:1f wan: configuring for phy/gmii link mode
[   21.570619] 8021q: adding VLAN 0 to HW filter on device wan
[   21.585077] br-wan: port 5(wan) entered blocking state
[   21.595446] br-wan: port 5(wan) entered disabled state
[   21.607353] device wan entered promiscuous mode
[   23.072402] mt7615 DBDC: 1
[   23.077930] mt76_check_sband: band=0 n_channels=14
[   23.087589] mt76_check_sband: band=1 n_channels=27
[   23.097165] mt7615_register_ext_phy
[   25.610530] mt7530 mdio-bus:1f lan4: Link is Up - 1Gbps/Full - flow control rx/tx

  541 root         0 SWN  [jffs2_gcd_mtd6]
  626 root      1252 S    /sbin/ubusd
  627 root      1256 S    /bin/ash --login
  644 root      1044 S    /sbin/urngd
  682 root         0 IW   [kworker/3:2-eve]
  778 root         0 IW<  [cfg80211]
  795 root         0 SW   [mt76-tx phy0]
  800 root         0 IW<  [kworker/u9:1-na]
  995 root      1264 S    /sbin/logd -S 64
 1032 root      2080 S    /sbin/rpcd -s /var/run/ubus.sock -t 30
 1074 root         0 IW<  [kworker/1:2H]
 1127 dnsmasq   1436 S    /usr/sbin/dnsmasq -C /var/etc/dnsmasq.conf.cfg01411c
 1168 root      1148 S    /usr/sbin/dropbear -F -P /var/run/dropbear.1.pid -p
 1235 root      1900 D    /usr/sbin/hostapd -s -g /var/run/hostapd/global
 1236 root      1872 S    /usr/sbin/wpa_supplicant -n -s -g /var/run/wpa_suppl
 1277 root      1696 S    /sbin/netifd
 1312 root      1488 S    /usr/sbin/odhcpd
 1351 root      1384 S    /bin/sh /etc/rc.common /etc/rc.d/S50qos boot
 1447 root         0 DW   [kworker/0:2+eve]
 1481 root      1292 S    /bin/sh /sbin/hotplug-call iface
 1482 root      1616 S    /bin/sh ./mac80211.sh mac80211 setup radio0 {"config
 1543 root      1292 S    /bin/sh /sbin/hotplug-call iface
 1546 root      1372 S    /bin/sh /etc/rc.common /etc/init.d/qos enabled
 1583 root      1248 S    flock 1000
 1623 root         0 IW   [kworker/3:3-eve]
 1911 root      1248 S    /bin/sh /usr/bin/qos-start
 1913 root      1248 S    /bin/sh /usr/bin/qos-stop
 1915 root      1248 S    /bin/sh /usr/bin/qos-stop
 1917 root      1624 D    tc qdisc show
 1919 root      1248 S    grep -E (hfsc|ingress)
 1921 root      1252 S    awk {print $5}
 1987 root      1248 D    ip link set dev wlan0 up
 1988 root         0 IW   [kworker/0:3-eve]
 1989 root      1248 R    ps

If I disable DBDC (in source code) in mt*.ko it won't stuck at all, and rmmod + reloading DBDC enabled mt*.ko won't stuck until after reboot as reported above

Start by reproducing the reboot sequence on the Phicomm K2P with MT7615D and DBDC enabled, then compare it with DBDC disabled or after unloading and reloading the module. Use the provided dmesg and process output to investigate the stall around ip link set dev wlan0 up and the mt76 driver. Done means wireless setup no longer hangs after a clean reboot with DBDC enabled.