[PATCH 2/2] ath10k: force passive scan on 5GHz for WCN3990

[Malte Schababerle <m.schababerle@gmail.com>]

WCN3990 firmware (WLAN.HL.3.2) has a bug where active scan does not
tune the radio on 5GHz non-DFS channels. The radio reports identical
rx_clear_count values across channels, indicating no RF tuning occurs.
As a result, no 5GHz networks are discovered during active scan.

Passive scan works correctly on all 5GHz channels: the radio tunes
properly and rx_clear_count varies as expected.

Force passive scan mode for all 5GHz channels on WCN3990 using
QCA_REV_WCN3990(). DFS channels are already passive, so the effective
change is for non-DFS 5GHz channels only. This follows the pattern
established for WCN3990 firmware workarounds in thermal.c.

Tested on OnePlus 7T (SM8150/WCN3990) with WLAN.HL.3.2.0.c2-00006
and WLAN.HL.3.2.0.c2-00011:
- 5GHz passive scan discovers APs reliably (e.g. ch116/5580 MHz)
- Association to 5GHz networks succeeds
- No change to 2.4GHz or DFS channel behavior

Signed-off-by: Malte Schababerle <m.schababerle@gmail.com>
---
 drivers/net/wireless/ath/ath10k/mac.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
index 24dd794e31ea2..f6829232f6b15 100644
--- a/drivers/net/wireless/ath/ath10k/mac.c
+++ b/drivers/net/wireless/ath/ath10k/mac.c
@@ -3441,6 +3441,14 @@ static int ath10k_update_channel_list(struct ath10k *ar)
 			passive = channel->flags & IEEE80211_CHAN_NO_IR;
 			ch->passive = passive;
 
+			/* Force passive scan on 5GHz to work around WCN3990
+			 * firmware bug where active scan doesn't tune the
+			 * radio on 5GHz non-DFS channels.
+			 */
+			if (QCA_REV_WCN3990(ar) &&
+			    band == NL80211_BAND_5GHZ)
+				ch->passive = true;
+
 			/* the firmware is ignoring the "radar" flag of the
 			 * channel and is scanning actively using Probe Requests
 			 * on "Radar detection"/DFS channels which are not
-- 
2.47.3