Gentoo and Intel Corporation Centrino Advanced-N 6235
emerge sys-kernel/linux-firmware and locate iwlwifi-6000g2b-6.ucode (which sould be located at /lib64/firmware/iwlwifi-6000g2b-6.ucode)
set the following options in your kernel config.
Device Drivers --->
Generic Driver Options --->
-*- Userspace firmware loading support
[*] Include in-kernel firmware blobs in kernel binary
(iwlwifi-6000g2b-6.ucode) External firmware blobs to build into the kernel binary
(/lib64/firmware) Firmware blobs root directory
[*] Fallback user-helper invocation for firmware loading
[*] Network device support --->
[*] Wireless LAN --->
<M> Intel Wireless WiFi Next Gen AGN - Wireless-N/Advanced-N/Ultimate-N (iwlwifi)
<M> Intel Wireless WiFi DVM Firmware support
If it work you should see somthing similar within dmesg like this:
[ 3.695960] iwlwifi 0000:03:00.0: Detected Intel(R) Centrino(R) Advanced-N 6235 AGN, REV=0xB0
...
[ 40.945526] iwlwifi 0000:03:00.0: L1 Disabled - LTR Disabled
[ 40.953509] iwlwifi 0000:03:00.0: Radio type=0x2-0x1-0x0
[ 41.226936] iwlwifi 0000:03:00.0: L1 Disabled - LTR Disabled
[ 41.233974] iwlwifi 0000:03:00.0: Radio type=0x2-0x1-0x0
References:
https://wireless.wiki.kernel.org/en/users/Drivers/iwlwifi
https://forums.gentoo.org/viewtopic-p-7715914.html
https://forums.gentoo.org/viewtopic-t-1001638.html
https://forums.gentoo.org/viewtopic-t-1023622.html
https://fitzcarraldoblog.wordpress.com/2012/09/08/how-to-install-the-linux-firmware-package-in-gentoo/