Wifi on Linux 2.6.32

Background

Basically wireless doesn't work for many WiFi adaptors in the Linux 2.6.32 or similar kernels. To solve this problem, the Linux kernel wireless group created compat-wireless, which is a backport of kernel modules and drivers for the newest Linux kernel. After a while other non-wifi driver needed to be backported, so the effort was renamed compat-drivers. Finally they settled on the name backports.

This HowTo shows which packages are used with Linux 2.6.32 to support recently introduced WiFi modules, along with the configuration needed.

backports package

I used backports version 3.12.2-1 using allmodconfig for the DEFCONFIG. Before building the package, make sure your kernel configuration (linux*/.config) has the following entries:

CONFIG_NET_SCHED=y
CONFIG_CFG80211=m
CONFIG_MII=m

If you are using the RidgeRun SDK, the following command will dump the three lines above:

egrep 'CONFIG_NET_SCHED=|CONFIG_CFG80211=|CONFIG_MII=' $DEVDIR/bsp/mach/bspconfig

Configuring backports in RidgeRun SDK

In Kernel configuration -> Networking support -> Networking options ->

• QoS and/or fair queueing (build into kernel)

Kernel configuration -> Networking support -> Wireless ->

• cfg80211 (build as module)

Kernel configuration -> Device Drivers -> Network device support -> Ethernet (10 or 100Mbit)

• Generic Media Independent Interface device support

For defconfig-cw1200, I also needed USB Ethernet enabled (CONFIG_USB_USBNET=m)

Kernel configuration -> Device Drivers -> Network device support -> USB Network Adapters

• Multi-purpose USB Networking Framework

Configuring backports

The backport supported configurations, as reported by the backports make help target, includes:

Configuration targets:
  menuconfig      - Update current config utilising a menu based program
  allyesconfig    - New config where all options are accepted with yes
  oldconfig       - Update current config utilising a provided .config as base
  silentoldconfig - Same as oldconfig, but quietly, additionally update deps
  allnoconfig     - New config where all options are answered with no
  allmodconfig    - New config selecting modules when possible
  alldefconfig    - New config with all symbols set to default
  randconfig      - New config with random answer to all options
  listnewconfig   - List new options
  olddefconfig    - Same as silentoldconfig but sets new symbols to their default value

The defconfig-help backports make defconfig-help target lists the supported configurations. Example output is:

Driver or subsystem configuration targets:
  defconfig-alx
  defconfig-ar5523
  defconfig-ath10k
  defconfig-ath5k
  defconfig-ath6kl
  defconfig-ath9k
  defconfig-b43
  defconfig-b43legacy
  defconfig-brcmfmac
  defconfig-brcmsmac
  defconfig-carl9170
  defconfig-cw1200
  defconfig-ieee802154
  defconfig-iwlwifi
  defconfig-media
  defconfig-nfc
  defconfig-regulator
  defconfig-rtlwifi
  defconfig-wifi
  defconfig-wil6210
  defconfig-wwan

For the Sagrad SG901-1091 WiFi SDIO module, I used defconfig-cw1200.

backports usage

The details of how to use hardware that relies on backport is dependent on the hardware being supported. Various hardware devices are shown below.

Sagrad SG901-1091 WiFi SDIO module

Using defconfig-cw1200 created the kernel modules needed to support the Sagrad SG901-1091 WiFi SDIO module. I also installed linux-firmware as the cw1200 driver set needs the firmware file wsm_22.bin.

Plugging in the SDIO card causes the kernel to report:

mmc0: new SDIO card at address 0001

To verify information regarding the SDIO card:

cd /sys/devices/platform/davinci_mmc.0/mmc_host/mmc0/mmc0:0001/mmc0:0001:1
echo class: `cat class`, vendor: `cat vendor`, device: `cat device`

With the response:

class: 0x00, vendor: 0x0020, device: 0x2280

The debugfs file system contains entries that contain the current settings for the MMC/SD/SDIO interface of interest.

mount -t debugfs none /sys/kernel/debug
cat /sys/kernel/debug/mmc0/ios

With the expected output:

clock:		25000000 Hz
vdd:		20 (3.2 ~ 3.3 V)
bus mode:	2 (push-pull)
chip select:	0 (don't care)
power mode:	2 (on)
bus width:	2 (4 bits)
timing spec:	0 (legacy)

Load the appropriate set of drivers:

COMPAT_KDIR=/lib/modules/2.6.32-17-ridgerun/updates

insmod $COMPAT_KDIR/compat/compat.ko
insmod $COMPAT_KDIR/net/wireless/cfg80211.ko
insmod $COMPAT_KDIR/net/mac80211/mac80211.ko

insmod $COMPAT_KDIR/drivers/net/wireless/cw1200/cw1200_core.ko
insmod $COMPAT_KDIR/drivers/net/wireless/cw1200/cw1200_wlan_sdio.ko

The filtered output is shown below:

Loading modules backported from Linux version v3.12.2-0-g050dcf4
Backport generated by backports.git v3.12.2-1-0-gb4b7ee5

cfg80211: Calling CRDA to update world regulatory domain

cw1200_wlan_sdio: Probe called
CW1x00 Cut 2.2 silicon detected.
cw1200_wlan_sdio mmc0:0001:1: firmware: requesting wsm_22.bin
Firmware download completed.
CW1200 WSM init done.
   Input buffers: 8 x 1632 bytes
   Hardware: 261.5
   WSM firmware [WSM_A30.02.0395_PTA4W Jun 18 2012 10:13:51], ver: 3002, build: 395,   api: 1044, cap: 0x000B
Registered as 'phy0'

At this point you can follow the general Linux WiFi configuration steps.

USB TL-WN722N WiFi dongle using chipset Atheros AR9271

After booting the target, plug in the USB dongle. Example output:

usb 1-1: new high speed USB device using musb_hdrc and address 3
usb 1-1: configuration #1 chosen from 1 choice

You can check the interface class is 09 using

cat /sys/devices/platform/musb_hdrc/usb1/1-0:1.0/bInterfaceClass 

Load the appropriate set of drivers:

COMPAT_KDIR=/lib/modules/2.6.32-17-ridgerun/updates
find $COMPAT_KDIR -name \*.ko

modprobe compat
modprobe compat_firmware_class
modprobe cfg80211
modprobe mac80211

modprobe ath
modprobe ath9k_hw
modprobe ath9k_common
modprobe ath9k_htc

The filtered output is shown below:

Loading modules backported from Linux version v3.12.2-0-g050dcf4
Backport generated by backports.git v3.12.2-1-0-gb4b7ee5
cfg80211: Calling CRDA to update world regulatory domain

At this point you can follow the general Linux WiFi configuration steps.

Starting up the wireless network

Once you have your wifi dongle's driver installed successfully the next step is configure linux wireless and network settings.

Reference: Table of iw commands

Start by verifying there is no connection

iw dev wlan0 link 

Expected output:

Not connected.

Power on the adaptor:

ifconfig wlan0 up

Scan for access points (limiting output):

iw dev wlan0 scan | fgrep SSID

Example output:

	SSID: MOTOROLA-C0D8B
	SSID: linksys

Connect to access point

Connect to an open access point

If your access point doesn't require a password, connections are easy!

AP=linksys
iw dev wlan0 connect "$AP"

Example output:

wlan0: authenticate with 00:13:10:ea:bd:66
wlan0: send auth to 00:13:10:ea:bd:66 (try 1/3)
wlan0: authenticated
cw1200_wlan_sdio mmc0:0001:1: wlan0: disabling HT as WMM/QoS is not supported by the AP
cw1200_wlan_sdio mmc0:0001:1: wlan0: disabling VHT as WMM/QoS is not supported by the AP
wlan0: associate with 00:13:10:ea:bd:66 (try 1/3)
wlan0: RX AssocResp from 00:13:10:ea:bd:66 (capab=0x401 status=0 aid=8)
wlan0: associated

Connect to an WEP encrypted access point

If you like weak security and have enabled WEP encryption, you can connect using:

AP=linksys
PASS=DEADBEEF
iw dev wlan0 connect "$AP" key 0:$PASS

Example output not shown as I have no AP's that use WEP.

Connect to WPA encrypted access point

You need to use The WPA supplicant. For netlink support, I used WPA supplicant 2.0 with libnl3.

cat <<EOF >/etc/wpa_supplicant/wpa_supplicant.conf
# Example wpa_supplicant 
network={
	ssid="Baily"
	psk="very secret passphrase"
	priority=5
}
EOF

wpa_supplicant -d -iwlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -Dnl80211 &

Assign IP address

You can use a DHCP client daemon or assign a fixed IP address. To assign a fixed IP address, use:

IP=10.0.0.221
ifconfig wlan0 $IP netmask 255.255.255.0

Testing

Measuring performance

On fast host PC:

ifconfig
iperf --server

On target device:

HOST_IP=10.0.0.4
iperf --client $HOST_IP

WiFi adaptor comparisions

I measured the following results. Note that for most embedded software / hardware configurations, iperf will consume 100% of the CPU as it tries to maximize the amount of data being exchanged every second.

Processor ! Adaptor	Test duration (-t100)	Bandwidth Mbits/sec (from iperf2)	CPU sys load (from top)	CPU IRQ load (from top)	CPU SIRQ load (from top)
DM368 (446 Mhz)	Built in Ethernet	88.7	45%	0%	55%
DM368 (446 Mhz)	TL-WN722N (Atheros AR9271)	19.7	16%	44%	40%