Alas, I'm giving up on Access Point function for XO1.5

[George Hunt]

The recent SD cards are so cheap, and wikipedia in various languages is
such a good replacement for the encyclopedia I devoured as a kid, I spent a
few weeks on this project.

The results were mixed, but just not good enough. The XO1.5 can act as a
gateway for a few minutes, or  a few hours (with apparently random delays
to the point of failure). But eventually, the libertas thinfirm driver, or
firmware, gets to be unresponsive, and only a reboot will correct the
situation.

*History*
The libertas AP function was developed by OLPC in the 2010 timeframe (and
used successfully by openfirmware for flashing many XO at a time). I'm not
clear whether "thinfirm" firmware was generated by marvel, or modfied by
outside consultant, cozybit under nondisclosure agreement., This firmware
may have removed some function, but added AP capability. The driver was
modified, in order to add the sdio interface (the OLPC motherboard uses
SDIO interface rather than the pre-existing usb driver interface). The
thinfirm driver (with USB interface) has been upstreamed, and accepted into
the kernel.  But the SDIO interface modifications to the driver have not.
More recently discovered sdio code has not been tried (2) -- or maybe it's
the same in a different package.

Olpc documentation of the AP function existed, and I tried to follow the
instructions (1)(4)(7)

Jerry Vonau found a patch for sdio interface to thinfirm, which was the one
I tested (5). If I were to continue, I'd probably try the patch at (2)
since it's more recent.

There are references to setting the libertas_tf driver into debug mode,
which I did not pursue, since I'd need to learn a lot more about wireless
protocols, to make use of the debugging information.(6) But that's probably
what I would need to do if I continued.


*Random observation:*
   if a wifi client is connected to an XO1.5 acting as AP, and both the
client and the server are set to ping one another, the client ping delays
are constant. but the server delays are bi-modal, either 5ms or 230ms.

   1. http://wiki.laptop.org/go/Thinfirm_1.5
   2. http://www.sleepyrobot.com/?p=160 --
   3.
   http://dev.laptop.org/git/users/derosier/wireless-testing/tree/drivers/net/wireless/libertas_tf
   4. http://wiki.laptop.org/go/Libertas_Thinfirmware_HOWTO
   5. http://www.spinics.net/lists/linux-wireless/msg55208.html
   6.
   http://labs.isee.biz/index.php/How_to_setup_Marvell_88w8686_SDIO_wifi#How_to_debug_the_libertas_driver
   7. http://wiki.laptop.org/go/XO_as_AP
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