linux/kernel/common-config: support DFS radiations for ath(9|10)k drivers

This enables shady options because upstream and Atheros probably didn't fix the issue
and their idea of "certification" is quite extreme.

We follow OpenWRT here and apply those changes to reduce "WTFs/min" for users
wondering what is the difference between OpenWRT and NixOS for their APs.

This was tested on Qualcomm Atheros QCA986x/988x 802.11ac Wireless Network Adapter on a x86 machine
in the French regulatory domain on frequency 5600MHz, DFS was used successfully by hostapd
instead of a mind-boggling "device or resource busy" error which is what happens without those options.

1 files changed, 24 insertions, 12 deletions

diff --git a/pkgs/os-specific/linux/kernel/common-config.nix b/pkgs/os-specific/linux/kernel/common-config.nix
index 370e880963206..e0e4edc30fd93 100644
--- a/pkgs/os-specific/linux/kernel/common-config.nix
+++ b/pkgs/os-specific/linux/kernel/common-config.nix
@@ -281,18 +281,30 @@ let
     };
 
     wireless = {
-      CFG80211_WEXT         = option yes; # Without it, ipw2200 drivers don't build
-      IPW2100_MONITOR       = option yes; # support promiscuous mode
-      IPW2200_MONITOR       = option yes; # support promiscuous mode
-      HOSTAP_FIRMWARE       = option yes; # Support downloading firmware images with Host AP driver
-      HOSTAP_FIRMWARE_NVRAM = option yes;
-      ATH9K_PCI             = option yes; # Detect Atheros AR9xxx cards on PCI(e) bus
-      ATH9K_AHB             = option yes; # Ditto, AHB bus
-      B43_PHY_HT            = option yes;
-      BCMA_HOST_PCI         = option yes;
-      RTW88                 = whenAtLeast "5.2" module;
-      RTW88_8822BE          = mkMerge [ (whenBetween "5.2" "5.8" yes) (whenAtLeast "5.8" module) ];
-      RTW88_8822CE          = mkMerge [ (whenBetween "5.2" "5.8" yes) (whenAtLeast "5.8" module) ];
+      CFG80211_WEXT               = option yes; # Without it, ipw2200 drivers don't build
+      IPW2100_MONITOR             = option yes; # support promiscuous mode
+      IPW2200_MONITOR             = option yes; # support promiscuous mode
+      HOSTAP_FIRMWARE             = option yes; # Support downloading firmware images with Host AP driver
+      HOSTAP_FIRMWARE_NVRAM       = option yes;
+      ATH9K_PCI                   = option yes; # Detect Atheros AR9xxx cards on PCI(e) bus
+      ATH9K_AHB                   = option yes; # Ditto, AHB bus
+      # The description of this option makes it sound dangerous or even illegal
+      # But OpenWRT enables it by default: https://github.com/openwrt/openwrt/blob/master/package/kernel/mac80211/Makefile#L55
+      # At the time of writing (25-06-2023): this is only used in a "correct" way by ath drivers for initiating DFS radiation
+      # for "certified devices"
+      EXPERT                      = option yes; # this is needed for offering the certification option
+      CFG80211_CERTIFICATION_ONUS = option yes;
+      # DFS: "Dynamic Frequency Selection" is a spectrum-sharing mechanism that allows
+      # you to use certain interesting frequency when your local regulatory domain mandates it.
+      # ATH drivers hides the feature behind this option and makes hostapd works with DFS frequencies.
+      # OpenWRT enables it too: https://github.com/openwrt/openwrt/blob/master/package/kernel/mac80211/ath.mk#L42
+      ATH9K_DFS_CERTIFIED         = option yes;
+      ATH10K_DFS_CERTIFIED        = option yes;
+      B43_PHY_HT                  = option yes;
+      BCMA_HOST_PCI               = option yes;
+      RTW88                       = whenAtLeast "5.2" module;
+      RTW88_8822BE                = mkMerge [ (whenBetween "5.2" "5.8" yes) (whenAtLeast "5.8" module) ];
+      RTW88_8822CE                = mkMerge [ (whenBetween "5.2" "5.8" yes) (whenAtLeast "5.8" module) ];
     };
 
     fb = {