[Bug 217242] CPU hard lockup related to xhci/dma

[bugzilla-daemon@kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=217242

--- Comment #15 from Hunter M (miller.hunterc@gmail.com) ---
Created attachment 304127
  --> https://bugzilla.kernel.org/attachment.cgi?id=304127&action=edit
trb values

Found what (possibly) looks to be a similar issue at
https://github.com/raspberrypi/linux/is … 1241972882.

The comment I've linked has a similar scenario (in that the single serial port
communication occurs frequently - the comment stated the serial communication
frequency was every 0.2s; the communication I've implemented is every 0.15s).
Yesterday I had started the serial communication process and left it overnight
to see the trb values by performing

for d in /sys/kernel/debug/usb/xhci/0000:01:00.0/devices/*/*; do if [ -d "$d"
]; then cd $d; echo "${d/?*\/devices\//}: $(wc -l trbs)"; fi done

However, when coming back this morning and attempting the above command, the
computer froze and either the software or hardware watchdog kicked in and
restarted the computer (journalctl logs did not print out before the reboot
occurred, so unfortunately I don't have any information on what happened).

I went ahead and re-performed the test today reducing the sleep time in between
serial write calls from 0.15s to 0.05s. With that, the ttyACM ring size did
expand considerably. The values I was able to obtain until a power outage
occurred which stopped my test are attached.

Further information: utilizing Microchip MCP2200 USB to UART converter instead
of FTDI (though this should not make a difference, pointing it out just in
case).

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