ath9k: unable to connect to hidden SSID on DFS channel

Hello,

I have a project where I want to establish Wi-Fi connection to a
hidden SSID, on DFS channel.

I am running wpa_supplicant 2.9 on a device with:
"Linux 4.9.51-yocto-standard armv7l" and
"Network controller: Qualcomm Atheros AR958x 802.11abgn Wireless
Network Adapter (rev 01)"

Sounds an old project, I know, but want to bring this alive, if
possible. Unfortunately, connection to a hidden SSID on DFS channel
seems not working.

However, it works on a different, newer device, which has
"Linux raspberrypi 5.10.17-v7l+ armv7l" and
"PCI bridge: Broadcom Limited Device 2711 (rev 10)".

The wpa_supplicant on the two devices is mostly idem: same v2.9, same
runtime configuration, almost all config variables (wpa_cli dump)
match (not seen relevant difference). There might be compile option
difference, but don't think they are relevant.
The only thing I see is with driver flags, where the newer device
supports flags like DFS_OFFLOAD, BSS_SELECTION, or
4WWAY_HANDSHAKE_PSK, but the older device does not offer these.

So I suspect the issue is due to some of the above missing features in
my ath9k driver (have default driver provided by kernel).

Questions:
- is it possible to enable the above driver flags/features for ath9k?
If so, how to enable and are there patches for these?
- any hint where to look in ath9k driver for passive scanning
implementation? Is there another module/location where passive
scanning is implemented?
- any suggestions for a solution to my issue?

Thanks,
Koppany