Kernel message spew on reboot - Quectel EG25-G

[Bruce Johnson]

I am getting a kernel message spew on the console whenever I reboot one 
of my boxes that's equipped with a Quectel EG25-G modem:

> option1 ttyUSB0: usb_wwan_write: submit urb 0 failed: -19

When this happens, the reboot either does not complete or takes so long 
that it is unacceptable. It happens after the system has closed 
systemd-journald, so I haven't yet been able to find any additional 
information that might help.

If I stop ModemManager for a little while before issuing the reboot, 
this doesn't happen. I've tried juggling the shutdown order and timing 
of the relevant systemd services but haven't yet found a way to put in 
sufficient delay for a reboot to occur reliably.

My team is currently upgrading our project from Yocto's Dunfell branch 
to their Scarthgap branch. This takes us from Linux kernel 5.4.34 to 
6.6.23, and from ModemManager 1.18.4 to 1.22. Everything worked great in 
the old setup.

I'm not well acquainted with either body of source code (ModemManager or 
Linux kernel). Can anyone advise me on how I might be able to figure 
this out?

-- 
Bruce Johnson
Chantilly, Virginia
USA