iwlwifi 6235 AGN: hardware limitation on number of stations that can connect in ap mode ?

[Sander Eikelenboom <linux@eikelenboom.it>]

Hi Johannes,

I'm trying to use an Intel Corporation Centrino Advanced-N 6235 (rev 24) with 
openwrt and hostapd to provide router functionality.
That all works fine, except that it at max accepts 12 wireless clients.
I have tried a few kernels (including 3.18-rc7) and versions of openwrt 
(including trunk) already, but all to no avail.

So i'm wondering is there a hardware limitation of stations that can connect to 
this mini-pci card in ap-mode ?

[   10.621530] iwlwifi 0000:00:05.0: loaded firmware version 18.168.6.1 op_mode iwldvm
[   10.621546] iwlwifi 0000:00:05.0: CONFIG_IWLWIFI_DEBUG enabled
[   10.621548] iwlwifi 0000:00:05.0: CONFIG_IWLWIFI_DEBUGFS enabled
[   10.621549] iwlwifi 0000:00:05.0: CONFIG_IWLWIFI_DEVICE_TRACING disabled
[   10.621550] iwlwifi 0000:00:05.0: Detected Intel(R) Centrino(R) Advanced-N 6235 AGN, REV=0xB0
[   10.621976] iwlwifi 0000:00:05.0: L1 Disabled - LTR Disabled
[   10.640696] cfg80211: Ignoring regulatory request set by core since the driver uses its own custom regulatory domain
[   10.640832] ieee80211 phy0: Selected rate control algorithm 'iwl-agn-rs'
...
[   10.654858] lib80211: common routines for IEEE802.11 drivers
[   10.654859] lib80211_crypt: registered algorithm 'NULL'
[   10.654864] lib80211_crypt: registered algorithm 'WEP'
[   10.654866] lib80211_crypt: registered algorithm 'CCMP'
[   10.654869] lib80211_crypt: registered algorithm 'TKIP'
..
[   31.016196] cfg80211: Calling CRDA to update world regulatory domain
[   32.253288] iwlwifi 0000:00:05.0: L1 Disabled - LTR Disabled
[   32.364036] iwlwifi 0000:00:05.0: Radio type=0x2-0x1-0x0
[   33.008507] iwlwifi 0000:00:05.0: L1 Disabled - LTR Disabled
[   33.116331] iwlwifi 0000:00:05.0: Radio type=0x2-0x1-0x0


the first clients connect perfectly well but after 12 client have connected, for 
the 13th i get:

[  784.301106] wlan0: Allocated STA 00:0d:f0:2e:ee:02
[  784.301117] wlan0: moving STA 00:0d:f0:2e:ee:02 to state 2
[  784.301122] wlan0: moving STA 00:0d:f0:2e:ee:02 to state 3
[  784.301141] iwlwifi 0000:00:05.0: Unable to prepare station 00:0d:f0:2e:ee:02 for addition
[  784.481399] iwlwifi 0000:00:05.0: Unable to add station 00:0d:f0:2e:ee:02 (-22)
[  784.647835] wlan0: Destroyed STA 00:0d:f0:2e:ee:02
[  785.828588] wlan0: Allocated STA 00:0d:f0:2e:ee:02
[  785.828600] wlan0: moving STA 00:0d:f0:2e:ee:02 to state 2
[  785.828605] wlan0: moving STA 00:0d:f0:2e:ee:02 to state 3
[  785.828624] iwlwifi 0000:00:05.0: Unable to prepare station 00:0d:f0:2e:ee:02 for addition
[  786.044379] iwlwifi 0000:00:05.0: Unable to add station 00:0d:f0:2e:ee:02 (-22)
[  786.219632] wlan0: Destroyed STA 00:0d:f0:2e:ee:02

The firmware seems to be the latest available for download.

If this isn't a hardware limitation, could you give a pointer to the debug 
values to use so i can get the debug output you would be interested in ?

If it is a hardware limitation, are there any other intel mini-pci adapters that 
don't have this hardware limitation (or at least a highter one).

--
Sander


lspci:

00:05.0 Network controller: Intel Corporation Centrino Advanced-N 6235 (rev 24)
        Subsystem: Intel Corporation Centrino Advanced-N 6235 AGN
        Physical Slot: 5
        Flags: bus master, fast devsel, latency 0, IRQ 70
        Memory at f3090000 (64-bit, non-prefetchable) [size=8K]
        Capabilities: [c8] Power Management version 3
        Capabilities: [d0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [e0] Express Endpoint, MSI 00
        Kernel driver in use: iwlwifi