[Android Software/Hacking General [Developers Only]] v8dave:
I have custom 3.4.49 kernel with Android 5.1 and for some reason, I broke it and now the modem ports do not appear in /dev

This is the debug output I see with custom kernel:

<6>[ 2.868000] usbcore: registered new interface driver usbserial

<6>[ 2.876000] usbcore: registered new interface driver usbserial_generic

<6>[ 2.884000] USB Serial support registered for generic

<6>[ 2.944000] usb 1-1.2: new high-speed USB device number 3 using nxp-ehci

<6>[ 3.052000] usb 1-1.2: New USB device found, idVendor=1e0e, idProduct=9001

<6>[ 3.052000] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

<6>[ 3.060000] usb 1-1.2: Product: SimTech, Incorporated

<6>[ 3.064000] usb 1-1.2: Manufacturer: SimTech, Incorporated

<6>[ 3.068000] usb 1-1.2: SerialNumber: 0123456789ABCDEF

<6>[ 3.076000] usbserial: USB Serial Driver core

<6>[ 3.080000] usbcore: registered new interface driver ch341

<6>[ 3.084000] USB Serial support registered for ch341-uart

<6>[ 3.088000] usbcore: registered new interface driver cp210x

<6>[ 3.096000] USB Serial support registered for cp210x

<6>[ 3.100000] usbcore: registered new interface driver ftdi_sio

<6>[ 3.104000] USB Serial support registered for FTDI USB Serial Device

<6>[ 3.112000] ftdi_sio: v1.6.0:USB FTDI Serial Converters Driver

<6>[ 3.116000] usbcore: registered new interface driver option

<6>[ 3.124000] USB Serial support registered for GSM modem (1-port)

<6>[ 3.128000] usbcore: registered new interface driver pl2303

<6>[ 3.136000] USB Serial support registered for pl2303

<6>[ 3.140000] usbcore: registered new interface driver ti_usb_3410_5052

<6>[ 3.148000] USB Serial support registered for TI USB 3410 1 port adapter

<6>[ 3.152000] USB Serial support registered for TI USB 5052 2 port adapter

<6>[ 3.160000] ti_usb_3410_5052: v0.10:TI USB 3410/5052 Serial Driver

Now, if I load back the original kernel, then this is what I see in the debug output.

[ 2.936000] usbcore: registered new interface driver usbserial

[ 2.940000] usbcore: registered new interface driver usbserial_generic

[ 2.948000] USB Serial support registered for generic

[ 3.012000] usb 1-1.2: new high-speed USB device number 3 using nxp-ehci

[ 3.124000] usb 1-1.2: New USB device found, idVendor=1e0e, idProduct=9001

[ 3.124000] usb 1-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3

[ 3.132000] usb 1-1.2: Product: SimTech, Incorporated

[ 3.136000] usb 1-1.2: Manufacturer: SimTech, Incorporated

[ 3.144000] usb 1-1.2: SerialNumber: 0123456789ABCDEF

[ 3.152000] usbserial: USB Serial Driver core

[ 3.152000] usbcore: registered new interface driver ch341

[ 3.156000] USB Serial support registered for ch341-uart

[ 3.164000] usbcore: registered new interface driver cp210x

[ 3.168000] USB Serial support registered for cp210x

[ 3.172000] usbcore: registered new interface driver ftdi_sio

[ 3.180000] USB Serial support registered for FTDI USB Serial Device

[ 3.184000] ftdi_sio: v1.6.0:USB FTDI Serial Converters Driver

[ 3.192000] usbcore: registered new interface driver option

[ 3.196000] USB Serial support registered for GSM modem (1-port)

[ 3.204000] option 1-1.2:1.0: GSM modem (1-port) converter detected

[ 3.208000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB0

[ 3.216000] option 1-1.2:1.1: GSM modem (1-port) converter detected

[ 3.220000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1

[ 3.228000] option 1-1.2:1.2: GSM modem (1-port) converter detected

[ 3.236000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2

[ 3.244000] option 1-1.2:1.3: GSM modem (1-port) converter detected

[ 3.248000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3

[ 3.256000] option 1-1.2:1.4: GSM modem (1-port) converter detected

[ 3.260000] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB4

[ 3.268000] usbcore: registered new interface driver pl2303

[ 3.272000] USB Serial support registered for pl2303

[ 3.280000] usbcore: registered new interface driver ti_usb_3410_5052

[ 3.284000] USB Serial support registered for TI USB 3410 1 port adapter

[ 3.292000] USB Serial support registered for TI USB 5052 2 port adapter

[ 3.300000] ti_usb_3410_5052: v0.10:TI USB 3410/5052 Serial Driver

Right after [ 3.196000] USB Serial support registered for GSM modem (1-port), the 5 ttyUSB ports are listed. So what am I missing from the kernel build that is failing to handle the modem and add the ports? The Android build is identical and only the kernel has been changed.

I've uploaded the complete debug capture for both here if that will help to narrow this down.

http://www.axoninstruments.biz/download/ttyUSB-notdetected.txt

http://www.axoninstruments.biz/download/ttyUSB-detected.txt