I recently updated my RPi2 after a long while, which bumped up the kernel to 4.4.x. After rebooting my USB wireless dongle refused to connect at all, either via wicd or manually with wpa_supplicant.
I'll skip the hand-wringing and debugging I did along the way, but it appears there is a problem with the the non-mainline 8192cu driver used in the Raspberry Pi kernel tree in more recent kernel versions. The gap between updates on my Pi was long enough, and I've since lost the history, such that I can't pin it down to a specific update. However switching back to the in-tree rlt8192cu driver let my dongle connect again without issue.
My wireless dongle appears as:
$this->bbcode_second_pass_code('', '$ lsusb
Bus 001 Device 004: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter ')
If anyone else is running into the same issue, I switched back to the in-tree driver by copying the linux-raspberrypi PKGBUILD and adding two patches that revert the commits that force the out-of-tree driver, which are:
07ca0b6 "net: Fix rtl8192cu build errors on other platforms", and
d6cc7e5 "net: Add non-mainline source for rtl8192cu wlan".
I also switched to the rpi-4.5.y branch while I was at it - I don't know if this makes a difference, there are some realtek-related differences between 4.4 and 4.5, but I wasn't going to compile too many kernels on the Pi.
Obviously the real solution will be to work out why the out-of-tree driver is unhappy, and/or switch to the in-tree driver by default, but for now my wireless works again
