rtwn: add radar detection support for RTL8821AU (disabled by default)

[avos]

Summary

The register access sequence is the same as in the 4.3.22-beta rtlwifi driver (core/rtw_odm.c file, code under CONFIG_DFS_MASTER ifdef); actually it was tested only in AP mode with no STAs.

By default it is disabled; to enable it, dev.rtwn.%d.radar_detection tunable need to be set to a nonzero value.

Test Plan

No radar events were seen - so, I have no idea if it is really correct / working.

[adrian]

Hm, so does the firmware do the DFS radar detection and return "radar found", or is it like the atheros chips and just returning pulses, and some userland detector has to fire?

This is something the USB NIC does, right? Maybe I can set up next week here to see. I can generate FCC pulses at the very least.

What's the vendor code doing?

-adrian

[avos]

Yes, this is USB NIC.

As I can see, the vendor code:

1. when channel is selected and radar detection is required - calls rtw_odm_radar_detect_enable() (writes some values into few undocumented registers).
2. when AP is started - starts a timer with 100 ms period, where checks 17th bit from another undocumented register.
3. if the bit is set (== radar is detected):
   • resets radar detection;
   • refreshes non-occupancy list
   • recreates the BSS.

P.S. BTW, the 'radar event' is ignored if there was too much data (Tx + Rx) during last timer period; this is not implemented here yet.

[adrian]

interesting, ok. I bet it's just detecting a pulse. I'll go look at it on the scope next week.