hostapd + channel bonding + 5GHz

[Lara Deek]

Hello,

The ht_capab parameter in hostapd.conf enables 40MHz operation
([HT40-][HT40+]). I understand hostapd enables channel bonding only if there
will be no channel/bandwidth overlap with neighboring APs (802.11n: scan for
overlapping BSSes before starting 20/40MHz channel). Is there some way where
I can control 40MHz vs. 20MHz operation myself without it being censored by
hostapd?

Basically, I just want to be able to control channel bandwidth and operating
channel using "iw dev wlan1 set freq 5745 HT20/HT40-/HT40+" while hostapd is
running, and without being censored by hostapd. Is there any way to
accomplish this? Is it a sensible option to resort to older 0.6.x
distributions where there was just added support for configuring secondary
channel offset for HT40? I am currently running hostapd v0.8.x, and these
co-existence checks that limit the use of 40MHz were added in 0.7.x. If it
is not a sensible option, I can alternatively modify
hw_features.c (particularly the "ieee80211n_check_40mhz" function) and
hostapd.c for recent hostapd versions. However, I still want to be able to
control bandwidth operation with "iw".

My PC card supports: HT20/HT40, RC HT40 SGI, DSSS/CCK HT40. My ht_capab =
[HT40-][HT40+][DSSS_CCK-40]. The iw list output for my PC card is:

Capabilities: 0x104e

HT20/HT40
SM Power Save disabled
RX HT40 SGI
No RX STBC
Max AMSDU length: 3839 bytes
DSSS/CCK HT40
Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
Minimum RX AMPDU time spacing: 8 usec (0x06)
HT TX/RX MCS rate indexes supported: 0-15
Frequencies:
* 5180 MHz [36] (17.0 dBm)
* 5200 MHz [40] (17.0 dBm)
* 5220 MHz [44] (17.0 dBm)
* 5240 MHz [48] (17.0 dBm)
* 5260 MHz [52] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5280 MHz [56] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5300 MHz [60] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5320 MHz [64] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5500 MHz [100] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5520 MHz [104] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5540 MHz [108] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5560 MHz [112] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5580 MHz [116] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5600 MHz [120] (disabled)
* 5620 MHz [124] (disabled)
* 5640 MHz [128] (disabled)
* 5660 MHz [132] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5680 MHz [136] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5700 MHz [140] (20.0 dBm) (passive scanning, no IBSS, radar detection)
* 5745 MHz [149] (30.0 dBm)
* 5765 MHz [153] (30.0 dBm)
* 5785 MHz [157] (30.0 dBm)
* 5805 MHz [161] (30.0 dBm)
* 5825 MHz [165] (30.0 dBm)
Bitrates (non-HT):
* 6.0 Mbps
* 9.0 Mbps
* 12.0 Mbps
* 18.0 Mbps
* 24.0 Mbps
* 36.0 Mbps
* 48.0 Mbps
* 54.0 Mbps

Given my hardware capabilities, I should be able to channel bond every
channel with its adjacent channel. Hostapd restricts channel bonding to
particular channels. Is there a reason for that? And how can I remove that
restriction?

Furthermore, according to the kernel logs, my EEPROM is set to US 0x3a (CRDA
updates the regulatory domain for my card I guess). Is this the reason why
the UNI-2 band is labeled as "(passive scanning, no IBSS, radar detection)"?
I want to ask if this is a limitation set by the ath9k driver, and not my
actual hardware. I would like to be able to use those channels to do DFS,
and was wondering if that was a software vs. hardware limitation.

I am sorry if I crammed too many questions in one email. Thank you for your
patience :)

Regards,
Lara
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