Message-ID: <518E0CD6.3040501@hauke-m.de> (sfid-20130511_111842_686422_9BFB7867)
Date: Sat, 11 May 2013 11:18:14 +0200
From: Hauke Mehrtens <hauke@hauke-m.de>
MIME-Version: 1.0
To: Arend van Spriel <arend@broadcom.com>
CC: JoSH Lehan <krellan@gmail.com>, linux-wireless@vger.kernel.org,
	"Luis R. Rodriguez" <mcgrof@do-not-panic.com>
Subject: Re: Using compat-drivers conflicts with kernel mac80211 and cfg80211
References: <CALOB5QZCeC7OTqkw5go6E_KUajVe5GDuCsSsc68cpZqE2YVfRQ@mail.gmail.com> <518DF4B1.3020706@broadcom.com>
In-Reply-To: <518DF4B1.3020706@broadcom.com>
Content-Type: text/plain; charset=ISO-8859-1
Sender: linux-wireless-owner@vger.kernel.org

On 05/11/2013 09:35 AM, Arend van Spriel wrote:
> On 05/11/2013 02:52 AM, JoSH Lehan wrote:
>> It seems I can choose to use the mac80211/cfg80211 that came with the
>> kernel,*or*, the mac80211/cfg80211 that come with compat-drivers.  Is
>> this correct?  I'll have to maintain these two mac80211/cfg80211
>> drivers in separate directories, since they have the same name, and it
>> will complicate my detection/loading script, but if there's no other
>> way, then this is what needs to be done.
> 
> Luis may correct me, but I think you are correct. compat-drivers
> provides a compat.ko which is the glue between new drivers and your
> kernel. With the new drivers you get new features provided you have new
> mac80211/cfg80211 as well. Hence the glue is between wireless modules
> (including mac80211/cfg80211) and rest of your kernel. On a non-embedded
> system the compat-driver modules are installed in a separate folder
> /lib/modules/<your_kernel_version/updates. depmod is run during the
> install in which this folder takes precedence.
> 
> Not sure what your use-case is. You have a system in which different
> wireless devices may be plugged in or ...?

You can only use mac80211/cfg80211 from compat-driver *or* the kernel.
There was a plan to rename all exported symbols and make it possible to
use both at the same time, but no one fully implemented it. The API
between mac80211/cfg80211 is not stable and changing very often to
implement new features so it is not possible to use new drivers with an
older version of mac80211/cfg80211 or the other way around.

compat.ko is not a glue it is more a module containing all the functions
not available in the kernel comopat-drivers was compiled against, but
needed by some drivers or frameworks like mac80211.

You should take all wireless drivers using mac80211/cfg80211 from
compat-drivers and not use the in kernel versions any more.

>> Could it be because I cross-compile compat-drivers?  Looking at the
>> installation scripts, it's clearly intended to be ran by the end user
>> to replace the drivers in their distribution with updated drivers, and
>> it could be that I missed something when tweaking it to cross-compile
>> the drivers and not install them locally.
> 
> Probably not, provided you build it for your kernel version.
> 
>> Has anybody else tried to use compat-drivers to build for an embedded
>> system?  If so, what's the recommended solution?  How to solve the
>> mac80211/cfg80211 problem, where the kernel-compiled mac80211/cfg80211
>> modules conflict with their equivalent compat-drivers modules?
> 
> Depends what you call an embedded system. We used it to run our driver
> on Android. Just cross-compiling it and install it on the system is what
> we did. Recently, there have been a number of people walking that path
> and contacting us. It may be an idea to have a compat-drivers feature to
> generate Android tarballs as it is always running a few kernel versions
> behind mainline.
> 
> Regards,
> Arend