The Atheros family of wireless chipsets finds its way into a number of
network adapters and laptop systems. It is a flexible and capable device,
with one little limitation: there is no free Linux driver available. Linux
support can be had via the freely-downloadable MadWifi driver
, but, at the core of that
driver, there is a binary-only "hardware access layer" (HAL) module which
does much of the real work. This module has all of the problems associated
with proprietary drivers: it cannot be audited or fixed, it cannot be
improved, it is only available for the kernel versions and architectures
supported by the manufacturer, etc. But, for Linux users, the choices are
MadWifi or nothing.
A free Atheros HAL module called "ar5k," written by Reyk Floeter, has been
in circulation for a couple of years; OpenBSD uses it. But this code has
long been followed by allegations that it was improperly developed and
potentially subject to copyright claims by Atheros. In the current
climate, nobody wants to risk bringing possibly tainted code into the
kernel; the potential consequences are just too severe. So, while the
desire to support Atheros devices in Linux remains strong, the existing HAL
has not been considered and little work has been done to bring that about.
Except that, as it turns out, work has been quietly happening in an
unexpected place. The Software Freedom Law Center was asked by the ar5k
developers to look at the development history of the code and come up with
a pronouncement on whether it was legitimate (from a copyright law
perspective) or not. On November 14, the SFLC produced its answer:
SFLC has made independent inquiries with the OpenBSD team regarding
the development history of ar5k source. The responses received
provide a reasonable basis for SFLC to believe that the OpenBSD
developers who worked on ar5k did not misappropriate code, and that
the ar5k implementation is OpenBSD's original copyrighted work.
This finding should clear the way for the entry of the free Atheros HAL
into the Linux kernel - eventually. But there are a couple of problems
which need to be overcome first.
One of those is the general level of upheaval in the Linux wireless subsystem.
The developers still intend to move over to the Devicescape stack and to
get that code into the mainline, but there is still work to be done in that
area. But a new wireless driver which does not work with Devicescape will
have a harder path into the kernel. There is an effort to move MadWifi
over to Devicescape (it's called "DadWifi"), so that might be the quickest
path for Atheros support to get into the kernel.
The other problem, however, is that code based on the HAL concept tends to
be unpopular at best. A HAL is typically seen as an unnecessary
abstraction layer between the driver and the hardware which serves to
obscure what's really going on while adding no real value of its own. So
developers who propose HAL-based drivers are usually told to go away and
come back once the HAL is gone. There is no real reason to expect things
to happen differently this time around.
But, even if it can't be used directly, the ar5k code is now fair game for
reference and eventual adaptation into a Linux driver. There are enough
developers out there with an interest in making Atheros adapters work
that the chances of this work getting done in the (relatively) near future
are relatively good. The list of devices which are not supported by Linux
is about to get shorter.
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