TOS 4 - how to reset USB3 bus?

Did you try TOS5.x? If the issue is present there as well could the USB controller be malfunctioning? The log on this node reads

xhci-hcd f10f0000.usb3: xHCI Host Controller
xhci-hcd f10f0000.usb3: new USB bus registered, assigned bus number 2
xhci-hcd f10f0000.usb3: hcc params 0x0a000990 hci version 0x100 quirks 0x0000000000010010
xhci-hcd f10f0000.usb3: irq 46, io mem 0xf10f0000
xhci-hcd f10f0000.usb3: xHCI Host Controller
xhci-hcd f10f0000.usb3: new USB bus registered, assigned bus number 3
xhci-hcd f10f0000.usb3: Host supports USB 3.0  SuperSpeed
xhci-hcd f10f8000.usb3: xHCI Host Controller
xhci-hcd f10f8000.usb3: new USB bus registered, assigned bus number 4
xhci-hcd f10f8000.usb3: hcc params 0x0a000990 hci version 0x100 quirks 0x0000000000010010
xhci-hcd f10f8000.usb3: irq 47, io mem 0xf10f8000
xhci-hcd f10f8000.usb3: xHCI Host Controller
xhci-hcd f10f8000.usb3: new USB bus registered, assigned bus number 5
xhci-hcd f10f8000.usb3: Host supports USB 3.0  SuperSpeed

I didn’t. TOS5 is not stable yet. The worst thing is that this happen randomly. It starts resetting the USB in loop and later fails with:

May  6 07:07:03 turris kernel: [   99.578204] xhci-hcd f10f0000.usb3: Max number of devices this xHCI host supports is 32.
May  6 07:07:03 turris kernel: [   99.586326] usb usb3-port1: couldn't allocate usb_device

There is something wrong with the kernel.

Well,
it happen again. Could be this a reason?

[141205.044912] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.147308] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.249702] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.352097] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.454491] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.556885] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.659279] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.761675] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.864064] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141205.966460] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.068851] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.171241] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.273640] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.376036] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.478437] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.580822] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.683210] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.785615] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.888015] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141206.990406] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.092798] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.195193] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.297586] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.399975] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.502374] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.604766] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.707161] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.809589] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141207.911953] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.008355] ath10k_pci 0000:02:00.0: Cannot communicate with firmware, attempting to fake crash and restart firmware.
[141208.019136] ath10k_pci 0000:02:00.0: firmware crashed! (uuid bddba077-b2c6-440f-9f7a-60b8ac38064e)
[141208.028227] ath10k_pci 0000:02:00.0: qca988x hw2.0 target 0x4100016c chip_id 0x043202ff sub 0000:0000
[141208.037567] ath10k_pci 0000:02:00.0: kconfig debug 0 debugfs 1 tracing 0 dfs 1 testmode 0
[141208.047003] ath10k_pci 0000:02:00.0: firmware ver 10.1-ct-8x-__fH-021-4fa9f30 api 2 features wmi-10.x,txstatus-noack,wmi-10.x-CT,ratemask-CT,regdump-CT,txrate-CT,flush-all-CT,pingpong-CT,ch-regs-CT,nop-CT,set-special-CT,get-temp-CT,tx-rc-CT,cust-stats-CT crc32 580c6146
[141208.071010] ath10k_pci 0000:02:00.0: board_file api 1 bmi_id N/A crc32 bebc7c08
[141208.078442] ath10k_pci 0000:02:00.0: htt-ver 2.2 wmi-op 2 htt-op 2 cal otp max-sta 128 raw 0 hwcrypto 1
[141208.089978] ath10k_pci 0000:02:00.0: firmware register dump:
[141208.095747] ath10k_pci 0000:02:00.0: [00]: 0x00940750 0x00400C00 0x00980000 0x009B6074
[141208.103784] ath10k_pci 0000:02:00.0: [04]: 0x009B60E4 0x009B6208 0x00941B6C 0x00941B20
[141208.111821] ath10k_pci 0000:02:00.0: [08]: 0x00941B00 0x009423A4 0x009422DC 0x009422C4
[141208.119862] ath10k_pci 0000:02:00.0: [12]: 0x00941B90 0x009423F4 0x009423D4 0x009423DC
[141208.127884] ath10k_pci 0000:02:00.0: [16]: 0x009423E4 0x009423EC 0x00942888 0x00942520
[141208.135925] ath10k_pci 0000:02:00.0: [20]: 0x009424FC 0x0094241C 0x00942540 0x00942498
[141208.143959] ath10k_pci 0000:02:00.0: [24]: 0x00942450 0x0094250C 0x009424D0 0x00942750
[141208.151992] ath10k_pci 0000:02:00.0: [28]: 0x00942798 0x00942844 0x009428C4 0x00942594
[141208.160028] ath10k_pci 0000:02:00.0: [32]: 0x0094258C 0x00942C28 0x00942F4C 0x00942F7C
[141208.168055] ath10k_pci 0000:02:00.0: [36]: 0x00942F90 0x00942FE4 0x00942FF8 0x00943040
[141208.176091] ath10k_pci 0000:02:00.0: [40]: 0x0094077C 0x00940790 0x00943084 0x00942F00
[141208.184132] ath10k_pci 0000:02:00.0: [44]: 0x009B6234 0x00942A80 0x00942D40 0x00942D64
[141208.192161] ath10k_pci 0000:02:00.0: [48]: 0x00942D78 0x00942D9C 0x00957E18 0x00957E28
[141208.200200] ath10k_pci 0000:02:00.0: [52]: 0x00957E20 0x00940788 0x009430EC 0x00000000
[141208.208237] ath10k_pci 0000:02:00.0: [56]: 0x00000000 0x00000000 0x00000000 0x00000000
[141208.216274] ath10k_pci 0000:02:00.0: Copy Engine register dump:
[141208.222314] ath10k_pci 0000:02:00.0: [00]: 0x00057400   2   2   3   3
[141208.228866] ath10k_pci 0000:02:00.0: [01]: 0x00057800  28  28 349 352
[141208.235426] ath10k_pci 0000:02:00.0: [02]: 0x00057c00  13  13   9  13
[141208.241979] ath10k_pci 0000:02:00.0: [03]: 0x00058000  30  30   0  30
[141208.248546] ath10k_pci 0000:02:00.0: [04]: 0x00058400 2367 2367 201 161
[141208.255267] ath10k_pci 0000:02:00.0: [05]: 0x00058800   3   3 386 387
[141208.261835] ath10k_pci 0000:02:00.0: [06]: 0x00058c00  29  29  29  29
[141208.268397] ath10k_pci 0000:02:00.0: [07]: 0x00059000   0   0   0   0
[141208.276995] ath10k_pci 0000:02:00.0: debug log header, dbuf: 0x4125fc  dropped: 0
[141208.285624] ath10k_pci 0000:02:00.0: [0] next: 0x4125e4 buf: 0x410a38 sz: 1500 len: 0 count: 0 free: 0
[141208.296052] ath10k_pci 0000:02:00.0: [1] next: 0x4125fc buf: 0x410448 sz: 1500 len: 0 count: 0 free: 0
[141208.329662] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.337095] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.344534] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.351969] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.359444] ath10k_pci 0000:02:00.0: failed to set preamble for vdev 0: -11
[141208.366676] ath10k_pci 0000:02:00.0: failed to send wmi nop: -108
[141208.373112] ath10k_pci 0000:02:00.0: failed to submit wmi echo: -108
[141208.379586] ath10k_pci 0000:02:00.0: failed to ping firmware: -108
[141208.385887] ath10k_pci 0000:02:00.0: failed to install key for vdev 0 peer 9c:da:3e:d4:b6:15: -108
[141208.394971] wlan0: failed to remove key (0, 9c:da:3e:d4:b6:15) from hardware (-108)
[141208.394978] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer ea083400 vdev: 0 addr: 78:02:f8:f5:6f:0c 
[141208.413843] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer c4372e00 vdev: 0 addr: 0c:7a:15:a3:8e:7d 
[141208.424933] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer d9a0c200 vdev: 0 addr: 9c:da:3e:d4:b6:15 
[141208.436018] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer e6b82c00 vdev: 0 addr: 40:4e:36:9b:a2:30 
[141208.447112] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer ea082200 vdev: 0 addr: 38:78:62:e6:18:08 
[141208.458201] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer e46d2000 vdev: 0 addr: 24:46:c8:4e:7d:90 
[141208.469288] ath10k_pci 0000:02:00.0: removing peer, cleanup-all, deleting: peer ed3aea00 vdev: 0 addr: 04:f0:21:32:3a:6b 
[141208.480442] ath10k_pci 0000:02:00.0: SWBA overrun on vdev 0, skipped old beacon
[141208.600269] ieee80211 phy0: Hardware restart was requested
[141209.629619] ath10k_pci 0000:02:00.0: 10.1 wmi init: vdevs: 16  peers: 127  tid: 256
[141209.646806] ath10k_pci 0000:02:00.0: wmi print 'P 128 V 8 T 410'
[141209.652958] ath10k_pci 0000:02:00.0: wmi print 'msdu-desc: 1424  sw-crypt: 0'
[141209.660231] ath10k_pci 0000:02:00.0: wmi print 'alloc rem: 26400 iram: 27140'
[141209.733512] ath10k_pci 0000:02:00.0: set-coverage-class, phyclk: 88  value: 0
[141210.628859] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141210.744493] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141210.753968] ath10k_pci 0000:02:00.0: device successfully recovered
[141210.761749] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141211.628842] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141214.628871] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141215.628879] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141216.628901] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141228.629249] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141230.629271] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141274.629761] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141503.631314] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141506.631379] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141507.631387] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141663.634085] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141695.634450] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[141741.635422] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[142112.639950] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[142563.646164] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[142932.648745] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[142970.649247] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[143779.657716] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[143783.657764] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[143922.659253] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[144032.661366] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[144719.659999] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[145161.664173] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[145462.666748] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[146218.602758] mv88e6085 f1072004.mdio-mii:10 lan4: Link is Down
[146218.608648] br-lan: port 5(lan4) entered disabled state
[146221.366718] mv88e6085 f1072004.mdio-mii:10 lan4: Link is Up - 10Mbps/Full - flow control rx/tx
[146221.375517] br-lan: port 5(lan4) entered blocking state
[146221.380861] br-lan: port 5(lan4) entered forwarding state
[146467.670864] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[147484.948464] mv88e6085 f1072004.mdio-mii:10 lan4: Link is Down
[147484.955683] br-lan: port 5(lan4) entered disabled state
[151221.683026] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[151223.683023] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[151526.681386] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[152096.680378] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[154667.682419] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[172894.799649] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[175706.831707] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[175707.831724] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[176497.838601] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[176498.838566] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[176499.838550] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[176543.469060] NFSD: Unable to create client record on stable storage: -110
[176836.838873] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[177155.837706] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[178690.834977] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[178694.834980] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read
[178875.835599] ath10k_pci 0000:02:00.0: dropping dbg buffer due to crash since read

Looks like too much errors for me.

Can you try running without the wifi card and observing if the USB bus problems occur again?