ACS toggling between success and failure

[Robert Campbell]

I'm seeing strange behavior with hw_mode=a and channel=any (full
config below) with runs of hostapd toggling between success and
failure.

I have a Atheros QCA6174 802.11ac card on Debian 10 with hostapd v2.8-devel.

The first run always results in failure:

    Configuration file: /etc/hostapd/hostapd.conf
    wlp4s0: interface state UNINITIALIZED->COUNTRY_UPDATE
    ACS: Automatic channel selection started, this may take a bit
    wlp4s0: interface state COUNTRY_UPDATE->ACS
    wlp4s0: ACS-STARTED
    ACS: Unable to collect survey data
    ACS: All study options have failed
    Interface initialization failed
    wlp4s0: interface state ACS->DISABLED
    wlp4s0: AP-DISABLED
    ACS: Possibly channel configuration is invalid, please report this
along with your config file.
    ACS: Failed to start
    wlp4s0: AP-DISABLED
    hostapd_free_hapd_data: Interface wlp4s0 wasn't started
    nl80211: deinit ifname=wlp4s0 disabled_11b_rates=0
    wlp4s0: interface state DISABLED->DISABLED
    wlp4s0: interface state DISABLED->DISABLED
    wlp4s0: AP-DISABLED
    wlp4s0: CTRL-EVENT-TERMINATING
    hostapd_free_hapd_data: Interface wlp4s0 wasn't started

With a second run always succeeding with:

    Configuration file: /etc/hostapd/hostapd.conf
    wlp4s0: interface state UNINITIALIZED->COUNTRY_UPDATE
    ACS: Automatic channel selection started, this may take a bit
    wlp4s0: interface state COUNTRY_UPDATE->ACS
    wlp4s0: ACS-STARTED
    wlp4s0: ACS-COMPLETED freq=5180 channel=36
    Using interface wlp4s0 with hwaddr 00:0e:8e:90:40:f9 and ssid "RRC_TEST"
    wlp4s0: interface state ACS->ENABLED
    wlp4s0: AP-ENABLED

    (I successfully connect)
    ^C

    wlp4s0: interface state ENABLED->DISABLED
    wlp4s0: AP-DISABLED
    wlp4s0: CTRL-EVENT-TERMINATING
    nl80211: deinit ifname=wlp4s0 disabled_11b_rates=0

with the above repeating indefinitely for all subsequent runs. My
config file is:

    #### Interface configuration ####
    interface=wlp4s0
    bridge=br0
    driver=nl80211

    ##### IEEE 802.11 related configuration #####
    ssid=RRC_TEST
    hw_mode=a
    channel=0
    auth_algs=1
    wmm_enabled=1
    country_code=CZ
    ieee80211d=1
    ieee80211h=0

    ##### IEEE 802.11n related configuration #####
    ieee80211n=1
    #require_ht=1

    ##### IEEE 802.11ac related configuration #####
    ieee80211ac=1
    #require_vht=1
    #vht_oper_chwidth=1
    #vht_oper_centr_freq_seg0_idx=42

    ##### WPA/IEEE 802.11i configuration #####
    wpa=2
    wpa_key_mgmt=WPA-PSK
    rsn_pairwise=CCMP
    wpa_passphrase=foobarbaz