[PATCH mt76-next 19/25] wifi: mt76: restart the beacon monitor of a link that gets a chanctx again

[Felix Fietkau <nbd@nbd.name>]

mt7996_vif_link_remove() keeps a station link when its chanctx is
unassigned, for example when mac80211 deactivates the link. The link
keeps its beacon_mon_interval and the beacon_mon_last of its last
beacon. When the link is activated again, mt7996_vif_link_add() takes
the reuse branch, which does not touch the beacon monitor. Unless a
beacon on that link arrives first, the next mt76_beacon_mon_check()
reports a beacon loss for the stale timestamp, and the station
disconnects:

  sta-mld0: CTRL-EVENT-BEACON-LOSS
  sta-mld0: CTRL-EVENT-DISCONNECTED bssid=a0:ad:9f:70:fb:4a reason=4 locally_generated=1

Reset beacon_mon_last whenever a link gets a chanctx, which
mt76_switch_vif_chanctx() already did after a channel switch. Do it
before the link points to the chanctx, since mt76_beacon_mon_check()
runs without dev->mutex and can see the link while vif_link_add() waits
for the firmware.

Fixes: 08813703ac41 ("wifi: mt76: mt7996: Destroy vif active links in mt7996_remove_interface()")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 drivers/net/wireless/mediatek/mt76/channel.c | 2 --
 drivers/net/wireless/mediatek/mt76/mt76.h    | 3 +++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/channel.c b/drivers/net/wireless/mediatek/mt76/channel.c
index a44773b9a49e..da111d37c4f5 100644
--- a/drivers/net/wireless/mediatek/mt76/channel.c
+++ b/drivers/net/wireless/mediatek/mt76/channel.c
@@ -258,8 +258,6 @@ int mt76_switch_vif_chanctx(struct ieee80211_hw *hw,
 		}
 
 		mt76_vif_link_ctx_set(mlink, v->new_ctx);
-		if (mlink->beacon_mon_interval)
-			WRITE_ONCE(mlink->beacon_mon_last, jiffies);
 	}
 
 out:
diff --git a/drivers/net/wireless/mediatek/mt76/mt76.h b/drivers/net/wireless/mediatek/mt76/mt76.h
index 42a1f84c5ca9..fb1b99f56e9c 100644
--- a/drivers/net/wireless/mediatek/mt76/mt76.h
+++ b/drivers/net/wireless/mediatek/mt76/mt76.h
@@ -2171,6 +2171,9 @@ static inline void
 mt76_vif_link_ctx_set(struct mt76_vif_link *mlink,
 		      struct ieee80211_chanctx_conf *conf)
 {
+	if (conf && mlink->beacon_mon_interval)
+		WRITE_ONCE(mlink->beacon_mon_last, jiffies);
+
 	/* pairs with smp_load_acquire() in mt76_vif_link_phy() */
 	smp_store_release(&mlink->ctx, conf);
 }
-- 
2.47.3