DFS start_dfs_cac() failed, -1 / nl80211: Failed to start radar detection: -16 (Device or resource busy)

[Krishna Chaitanya]

On Mon, Aug 25, 2014 at 6:25 PM, Conrad Kostecki <ck at conrad-kostecki.de> wrote:
>> ath10k supports 20, 40 and 80MHz bandwidths with radar detection.
>
> Hi Micha?,
>
> Thanks for your information! Maybe I will buy one ath10k card.
>
> I am unsure in one point regarding 5 GHz mode with my ath9k card. My current "iw list" show: (I am in regdomain DE)
>
> * 5180 MHz [36] (20.0 dBm)
> * 5200 MHz [40] (20.0 dBm)
> * 5220 MHz [44] (20.0 dBm)
> * 5240 MHz [48] (20.0 dBm)
> * 5260 MHz [52] (20.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5280 MHz [56] (20.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5300 MHz [60] (20.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5320 MHz [64] (20.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5500 MHz [100] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5520 MHz [104] (27.0 dBm) (no IR, radar detection)
>   DFS state: available (for 3826 sec)
> * 5540 MHz [108] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5560 MHz [112] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5580 MHz [116] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5600 MHz [120] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5620 MHz [124] (27.0 dBm) (no IR, radar detection)
>   DFS state: available (for 4106 sec)
> * 5640 MHz [128] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5660 MHz [132] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5680 MHz [136] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5700 MHz [140] (27.0 dBm) (no IR, radar detection)
>   DFS state: usable (for 6108 sec)
> * 5745 MHz [149] (disabled)
> * 5765 MHz [153] (disabled)
> * 5785 MHz [157] (disabled)
> * 5805 MHz [161] (disabled)
> * 5825 MHz [165] (disabled)
>
> Is this correct, that non-DFS channels are available and all "DFS" channels are per default no IR? Hostapd seems to work, at least there is no error with enabled DFS and it chooses a higher channel like 124. It this a correct behavior regarding, that the channel is marked as no IR? Or does this only mean, that until an applikation does not enable dfs, it can't use those channels?

"No-IR + radar detection" means we cannot initiate radiation
(transmission) without abiding the DFS rules like CAC. As the ath9k
has DFS support enabled, hostapd is starting fine. If the underlying
chip doesn't support DFS then hostapd fails in those channels.