Some ETSI countries have a small overlap in the wireless-regdb with an ETSI
channel (5590-5650). A good example is Australia:

  country AU: DFS-ETSI
  	(2400 - 2483.5 @ 40), (36)
  	(5150 - 5250 @ 80), (23), NO-OUTDOOR, AUTO-BW
  	(5250 - 5350 @ 80), (20), NO-OUTDOOR, AUTO-BW, DFS
  	(5470 - 5600 @ 80), (27), DFS
  	(5650 - 5730 @ 80), (27), DFS
  	(5730 - 5850 @ 80), (36)
  	(57000 - 66000 @ 2160), (43), NO-OUTDOOR

If the firmware (or the BDF) is shipped with these rules then there is only
a 10 MHz overlap with the weather radar:

* below: 5470 - 5590
* weather radar: 5590 - 5600
* above: (none for the rule "5470 - 5600 @ 80")

There are several wrong assumption in the ath11k code:

* there is always a valid range below the weather radar
  (actually: there could be no range below the weather radar range OR range
   could be smaller than 20 MHz)
* intersected range in the weather radar range is valid
  (actually: the range could be smaller than 20 MHz)
* range above weather radar is either empty or valid
  (actually: the range could be smaller than 20 MHz)

These wrong assumption will lead in this example to a rule

  (5590 - 5600 @ 20), (N/A, 27), (600000 ms), DFS, AUTO-BW

which is invalid according to is_valid_reg_rule() because the freq_diff is
only 10 MHz but the max_bandwidth is set to 20 MHz. Which results in a
rejection like:

  WARNING: at backports-20210222_001-4.4.60-b157d2276/net/wireless/reg.c:3984
  [...]
  Call trace:
  [<ffffffbffc3d2e50>] reg_get_max_bandwidth+0x300/0x3a8 [cfg80211]
  [<ffffffbffc3d3d0c>] regulatory_set_wiphy_regd_sync+0x3c/0x98 [cfg80211]
  [<ffffffbffc651598>] ath11k_regd_update+0x1a8/0x210 [ath11k]
  [<ffffffbffc652108>] ath11k_regd_update_work+0x18/0x20 [ath11k]
  [<ffffffc0000a93e0>] process_one_work+0x1f8/0x340
  [<ffffffc0000a9784>] worker_thread+0x25c/0x448
  [<ffffffc0000aedc8>] kthread+0xd0/0xd8
  [<ffffffc000085550>] ret_from_fork+0x10/0x40
  ath11k c000000.wifi: failed to perform regd update : -22
  Invalid regulatory domain detected

To avoid this, the algorithm has to be changed slightly. Instead of
splitting a rule which overlaps with the weather radar range into 3 pieces
and accepting the first two parts blindly, it must actually be checked for
each piece whether it is a valid range. And only if it is valid, add it to
the output array.

When these checks are in place, the processed rules for AU would end up as

  country AU: DFS-ETSI
          (2400 - 2483 @ 40), (N/A, 36), (N/A)
          (5150 - 5250 @ 80), (6, 23), (N/A), NO-OUTDOOR, AUTO-BW
          (5250 - 5350 @ 80), (6, 20), (0 ms), NO-OUTDOOR, DFS, AUTO-BW
          (5470 - 5590 @ 80), (6, 27), (0 ms), DFS, AUTO-BW
          (5650 - 5730 @ 80), (6, 27), (0 ms), DFS, AUTO-BW
          (5730 - 5850 @ 80), (6, 36), (N/A), AUTO-BW

and will be accepted by the wireless regulatory code.

Fixes: d5c65159 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20211112153116.1214421-1-sven@narfation.org