====== DFS Radar Detection ======

===== Issue =====

Disabled 5GHz after radar detection on Netgear R6220

<code>
hostapd: phy1-ap0: DFS-RADAR-DETECTED freq=5600 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5610 cf2=0
hostapd: phy1-ap0: AP-DISABLED
netifd: Network device 'phy1-ap1' link is down
kernel: br-lan: port 8(phy1-ap1) entered disabled state
kernel: device phy1-ap1 left promiscuous mode
kernel: br-lan: port 8(phy1-ap1) entered disabled state
hostapd: nl80211: Failed to remove interface phy1-ap1 from bridge br-lan: No such device
hostapd: nl80211: deinit ifname=phy1-ap0 disabled_11b_rates=0
kernel: device phy1-ap0 left promiscuous mode
kernel: br-lan: port 7(phy1-ap0) entered disabled state
netifd: Network device 'phy1-ap0' link is down
hostapd: phy1-ap0: interface state ENABLED->DISABLED
kernel: br-lan: port 7(phy1-ap0) entered blocking state
kernel: br-lan: port 7(phy1-ap0) entered disabled state
kernel: device phy1-ap0 entered promiscuous mode
kernel: br-lan: port 7(phy1-ap0) entered blocking state
kernel: br-lan: port 7(phy1-ap0) entered forwarding state
hostapd: phy1-ap0: interface state DISABLED->COUNTRY_UPDATE
hostapd: phy1-ap0: interface state COUNTRY_UPDATE->HT_SCAN
hostapd: phy1-ap0: interface state HT_SCAN->DFS
kernel: br-lan: port 7(phy1-ap0) entered disabled state
hostapd: phy1-ap0: DFS-NOP-FINISHED freq=5580 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5580 cf2=0
hostapd: phy1-ap0: interface state DFS->DFS
hostapd: phy1-ap0: DFS-NOP-FINISHED freq=5600 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5600 cf2=0
hostapd: phy1-ap0: interface state DFS->DFS
hostapd: phy1-ap0: DFS-CAC-START freq=5600 chan=120 sec_chan=-1, width=0, seg0=122, seg1=0, cac_time=60s
hostapd: phy1-ap0: DFS-NOP-FINISHED freq=5620 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5620 cf2=0
hostapd: phy1-ap0: interface state DFS->DFS
hostapd: phy1-ap0: DFS-CAC-START freq=5600 chan=120 sec_chan=-1, width=0, seg0=122, seg1=0, cac_time=60s
hostapd: phy1-ap0: DFS-NOP-FINISHED freq=5640 ht_enabled=0 chan_offset=0 chan_width=0 cf1=5640 cf2=0
hostapd: phy1-ap0: interface state DFS->DFS
hostapd: phy1-ap0: DFS-CAC-START freq=5600 chan=120 sec_chan=-1, width=0, seg0=122, seg1=0, cac_time=60s
hostapd: phy1-ap0: DFS-CAC-COMPLETED success=1 freq=5600 ht_enabled=0 chan_offset=0 chan_width=3 cf1=5610 cf2=0
</code>

Workaround to disable DFS is to switch to ''Panama'' country code:
<code>
iw reg get
global
country PL: DFS-ETSI
	(2400 - 2483 @ 40), (N/A, 20), (N/A)
	(5150 - 5250 @ 80), (N/A, 23), (N/A), NO-OUTDOOR, AUTO-BW
	(5250 - 5350 @ 80), (N/A, 20), (0 ms), NO-OUTDOOR, DFS, AUTO-BW
	(5470 - 5725 @ 160), (N/A, 26), (0 ms), DFS
	(5725 - 5875 @ 80), (N/A, 13), (N/A)
	(5945 - 6425 @ 160), (N/A, 23), (N/A), NO-OUTDOOR
	(57000 - 66000 @ 2160), (N/A, 40), (N/A)

uci set wireless.radio1.country='PA'
uci commit

iw reg get
global
country PA: DFS-FCC
	(2400 - 2483 @ 40), (N/A, 36), (N/A)
	(5150 - 5250 @ 80), (N/A, 36), (N/A), AUTO-BW
	(5250 - 5350 @ 80), (N/A, 30), (N/A), AUTO-BW
	(5470 - 5725 @ 160), (N/A, 30), (N/A)
	(5725 - 5850 @ 80), (N/A, 36), (N/A)
	(57000 - 64000 @ 2160), (N/A, 43), (N/A)
</code>

References:
  * https://www.reddit.com/r/openwrt/comments/twvf7i/dfsweather_radarsatellites_wifi_crashing/
  * https://www.reddit.com/r/openwrt/comments/rs9pit/dfs_radar_causes_5ghz_to_drop_and_it_doesnt_come/
  * https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/tree/db.txt
  * [[https://github.com/openwrt/openwrt/issues/14253|DFS start_dfs_cac() failed - wifi not enabled after 30 minute delay. #14253]]
  * https://github.com/openwrt/openwrt/issues/9864
  * [[https://github.com/NilsRo/Openwrt-radio-check|Openwrt-radio-check]]