I would like to recap some points that've already been shared in this
thread and also give some advice for those who want to use libre USB Wi-
Fi adapters with Debian GNU/Linux.
The best one can do with free software right now is 802.11n. There are
two main families of chipsets for USB wireless adapters, ath9k_htc
(AR7010 & AR9271) and "carl9170" (AR9170). The latter has some issues
with 802.11n setups, so the former should be preferred.
AR9271 is never dual-band capable; it is always 2.4GHz only. Whether an
AR7010 or AR9170 adapter is dual-band capable depends on what wireless
chip it is paired with. In general dual-band capable AR7010 adapters are
somewhat challenging to find, but dual-band AR9170 adapters are easy to
find.
For those interested in the technical details, ath9k_htc uses a custom
Xtensa CPU and as such requires a custom cross toolchain. Currently we
build this free firmware in Debian completely from source, which is
quite an achievement! I'm the current maintainer of open-ath9k-htc-
firmware in Debian (more on that package later), but much credit goes to
the former maintainer Oleksij Rempel, especially for his encouragement
of me. AR9170 uses an ordinary SuperH-2 CPU, and as such the carl9170
firmware can be built with a standard SuperH cross toolchain. I've
currently packaged gcc-sh-elf and binutils-sh-elf in Debian Unstable, so
that when I get around to it (or when someone I can mentor expresses
interest 😉️) we can build carl9170 from source as well.
The firmware for AR9170 (AKA carl9170) is currently shipped in the
firmware-linux-free package. However, due to complicated historical
reasons, the firmware for ath9k_htc is in a separate firmware-ath9k-htc
package, which tragically is not installed by default like all other
free firmware is. There is a common misconception that because ath9k_htc
adapters don't work out-of-the-box, but because the firmware also
happens to be in the non-free firmware-atheros package, that this is
actually non-free. That's not true; it's a fluke that the ath9k_htc
firmware is in firmware-atheros, and we're working to get it removed
from there.
So here's what I want to emphasize: if there's a chance you'll be using
an ath9k_htc adapter, install the firmware-ath9k-htc package. If you
don't know whether the adapter you have (or will have) has ath9k_htc,
installing that package won't hurt.
In general, for issues such as this, one should consult the Free
Software Foundation's Respects Your Freedom program, which certifies
devices that are guaranteed to be the best one can do with free
software. ThinkPenguin is just one of many vendors that sells USB
wireless adapters that work with free software+firmware.
Also, neither carl9170 nor ath9k_htc work with the Debian Installer
right now, so if one needs to install over Wi-Fi, the Live installer
should be considered.
Disclaimer: I have been compensated by ThinkPenguin, an FSF RYF vendor,
for my Debian wireless packaging work.
If anyone has questions on the matter, or would like to help with
wireless hacking, anyone is welcome to reach me privately.