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Old 09-17-2018, 05:33 PM   #1
lm1
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usbcore only registers new interface driver (cdc_wdm) when I hot-plug my device after bootup


Hi all,

If I wait until after bootup to plug in my USB modem, then usbcore registers the cdc_wdm driver interface and I'm able to use the USB modem as I want:

root@target:~#[ 60.630559] usb 1-1: new high-speed USB device number 2 using musb-hdrc
[ 60.993246] usbcore: registered new interface driver cdc_wdm
[ 61.013436] qmi_wwan 1-1:1.2: cdc-wdm0: USB WDM device
[ 61.038279] qmi_wwan 1-1:1.2 wwan0: register 'qmi_wwan' at usb-musb-hdrc.1-1, WWAN/QMI device, be:ce:e7:34:15:d8
[ 61.059967] usbcore: registered new interface driver qmi_wwan

root@target:~# lsusb
Bus 001 Device 002: ID 1bc7:1040 Telit Wireless Solutions

However, if I power-on/boot the embedded linux platform with the USB modem already plugged in, the device interface driver is never registered and I cannot use the USB modem:
...
[ 6.320320] usb 1-1: new high-speed USB device number 2 using musb-hdrc
...
root@target:~# lsusb
Bus 001 Device 002: ID 05c6:9008 Qualcomm, Inc. Gobi Wireless Modem (QDL mode)

Any help debugging this would be greatly appreciated. Why would the device interface driver (cdc_wdm) only get registered if plugging in the USB modem after booting? Is there a way to force the device interface driver (cdc_wdm) to register when powering up with the USB modem already plugged in? Is this something to do with udev, systemv/systemd/init, blacklisting?

Thanks in advance!
-Linux Noob
 
Old 09-18-2018, 08:15 AM   #2
rtmistler
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Count me in as someone who has tried to debug USB based cell modems and also found them to be difficult.

I don't know the reason for the differences between plug-in after boot versus plugged in before boot.

I would look into loading the cdc_wdm driver at some point during system initialization.

After usbcore has run, and since you likely need the network stack too, I'd say also after the point where the network stack is initialized.

Perhaps put it last in the initialization.
 
  


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