Re: Problem hanging Bulk IN, with USB 3.x, perhaps due to wMaxPacketSize = 1024 and wMaxBurst = 6 (OUT) and 2 (IN), tested and reproduceable with i.MX8MP and Raspberry Pi Compute Module 5 (CM5)

[Martin Maurer <martin.maurer@mmeacs.de>]

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Am 17.08.2025 um 16:58 schrieb Martin Maurer:
> Hello Michał, hello Mathias at all,
>
> many thanks for your answers!
>
> I have tried if I can reproduce it with a AMD Linux PC, but 
> unfortunately I was not able to reproduce (but setup is a bit different).
>
> So I went back to Raspberry Pi Compute Module 5, where I mainly 
> connected the radio module (Quectel RM520N-GL) via USB3,
>
> and installed a Wifi access point. All data/all connections from Wifi 
> access point are routed directly via wwan0 to radio module.
>
> This is currently my easiest setup to be able to reproduce the error. 
> Mostly in a few seconds.
>
> My knowledge in area Linux Kernel + USB is unfortunately not yet 
> enough to analyze and fix it by myself.
>
> But I used the help of ChatGPT-5 to create an usbmon and xhci kernel 
> trace.
>
> I create an usbmon trace as well as a trace from xhci (both recorded 
> in parallel):
>
> ... Removed due to spam website...

> This was the last output, my ping in a shell has shown:
>
> 64 bytes from 8.8.8.8: icmp_seq=2323 ttl=112 time=26.0 ms
> 64 bytes from 8.8.8.8: icmp_seq=2324 ttl=112 time=25.0 ms
> 64 bytes from 8.8.8.8: icmp_seq=2325 ttl=112 time=29.1 ms
> 64 bytes from 8.8.8.8: icmp_seq=2326 ttl=112 time=37.8 ms
>
> In parallel created more data traffic, but with ping I see first when 
> IP data connection does not work stable anymore.
>
> According to ChatGPT-5 the following places contain errors:
>
> *** USBMON ***
>
> In your usbmon_bus5_20250817-150158.log:
>
> First -71 (EPROTO) on the QMI Bulk-IN (Bi:5:005:14): line 2161, 
> timestamp 493245744
>
> 2161: ffffff8003c8cb40 493245744 C Bi:5:005:14 -71 0
>
> Just before that, there’s a -75 (EOVERFLOW) on the same IN EP, which 
> is often the first sign of trouble: line 2159, timestamp 493245221
>
> 2159: ffffff8003c8cd80 493245221 C Bi:5:005:14 -75 1024 = ...
>
> So the sequence is: several good completions → EOVERFLOW (-75) → then 
> a stream of EPROTO (-71) errors on Bi:5:005:14, which kills further 
> ping replies after your last good seq (2326).
>
>
> *** XHCI TRACE ***
>
> I found the first failure in your xHCI trace.
>
> First error line: line 8216
>
> Timestamp: 758267.000115
>
> Event: xhci_handle_event … type 'Transfer Event' … 'Error' … slot 1 ep 
> 29 … len 1472
>
> Why ep 29? In xHCI, the endpoint context index is ep_index = 2 * 
> ep_number + (direction), where direction is 0=OUT, 1=IN.
> So for Bulk IN ep 14: 2*14+1 = 29 → that’s your IN 0x87 pipe.
>
> Right after that line you can see the driver react:
>
> xhci_handle_transfer … length 1472 … (the failed TD)
>
> xhci_queue_command: Reset Endpoint Command … ep 29 (host tries to 
> recover)
>
> xhci_handle_event: … 'Command Completion Event' (reset completes)
>
> But from this point on, completions for that IN EP correspond to 
> usbmon -71 (EPROTO) — matching what you saw.
>
>
> Does this give a clue, where it could be coming from?
>
> It is 100% reproduceable in a few seconds on Raspberry Pi Ccompute 
> Module 5 (and I same behaviour on different kernel of i.MX8MP).
>
> Could it be a hardware problem? I already tried different radio module 
> (all Qualcomm, X62/X65 and X72/X75),
>
> different cables (all same length, all from same source), different 
> eval board for the M.2 radio modules (but from same source).
>
>
> Can you give me a hint, what to try next?
>
>
> ChatGPT-5 pinpoints me to try to disable LPM for USB3, could this be a 
> next step? Or is it something  else?
>
>
> Many thanks for your help!
>
> Best regards,
>
> Martin
>