root@raspberrypi:~# dmesg |grep -i tty
[    0.000000] Kernel command line: dma.dmachans=0x7f35 bcm2708_fb.fbwidth=656 bcm2708_fb.fbheight=416 bcm2708.boardrev=0xe bcm2708.serial=0x87754b72 smsc95xx.macaddr=B8:27:EB:75:4B:72 sdhci-bcm2708.emmc_clock_freq=100000000 vc_mem.mem_base=0x1ec00000 vc_mem.mem_size=0x20000000  dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait
[    0.000000] console [tty1] enabled
[    0.585151] dev:f1: ttyAMA0 at MMIO 0x20201000 (irq = 83) is a PL011 rev3
[    0.916637] console [ttyAMA0] enabled
root@raspberrypi:~# dmesg |grep -i ttyUSB
root@raspberrypi:~# modprobe usbserial vendor=sierra product=snd_bcm2835
root@raspberrypi:~# dmesg |grep -i ttyUSB
root@raspberrypi:~# lsusb
Bus 001 Device 002: ID 0424:9512 Standard Microsystems Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB
Bus 001 Device 071: ID 1199:0029 Sierra Wireless, Inc.