ath11k: Question about active scanning of DFS channels

[Alexander Wilhelm <alexander.wilhelm@westermo.com>]

Hello Developers,

I would like to investigate the following issue and would greatly appreciate
your support and feedback. I am using a QCN9074 chipset with the `ath11k` driver
and would like to use the background scan functionality in `wpa_supplicant`.
During my testing, I noticed that hidden access points operating on DFS channels
are not discovered. Even when I manually trigger a scan, I can only see the
hidden AP to which the client is currently connected. Other hidden APs remain
absent from the scan results.

Based on my research, DFS channels cannot be scanned passively, so I used a
sniffer to verify that the "directed" probe requests with given SSID were
actually being transmitted. I also confirmed that the hidden AP responded with a
probe response. However, despite receiving the probe response, the AP never
appears in the `scan_results` list reported by `wpa_supplicant`.

To further investigate, I modified the `ath11k` driver in the scan request
handling path `ath11k_wmi_start_scan_init()` as follows:

    -   arg->repeat_probe_time = 0;
    +   arg->repeat_probe_time = 50;
    +   arg->n_probes = 2;

After applying this changes, I was able to verify that two directed probe
requests were transmitted with a spacing of 50 ms between them. My main question
is how this use case is intended to work. At first glance, this does not appear
to be a driver bug. However, with the default configuration (repeat_probe_time =
0), the scan results do not seem to be updated as expected. Is this modification
to the `ath11k` driver considered valid, or is there a preferred way to handle
this scenario? Are there any `wpa_supplicant` parameters that should be adjusted
instead?

I would like to fully understand the intended behavior and the interaction
between `ath11k`, firmware, and `wpa_supplicant` in this case. Any insights,
recommendations, or background information would be greatly appreciated. Thank
you for your time and support.


Best regards
Alexander Wilhelm