wifi: wfx: implement wfx_remain_on_channel()

With some conditions, the device is able to send/receive frames during
scan operation. So, it is possible to use it implement the "remain on
channel" feature. We just ask for a passive scan (without sending any
probe request) on one channel.

This architecture allows to leverage some interesting features:
  - if the device is AP, the device switches channel just after the next
    beacon and the beacons are stopped during the off-channel interval.
  - if the device is connected, it advertises it is asleep before to
    switch channel (so the AP should stop to try to send data)
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231004172843.195332-9-jerome.pouiller@silabs.com

drivers/net/wireless/silabs/wfx/main.c

@@ -151,6 +151,8 @@ static const struct ieee80211_ops wfx_ops = {
 	.change_chanctx          = wfx_change_chanctx,
 	.assign_vif_chanctx      = wfx_assign_vif_chanctx,
 	.unassign_vif_chanctx    = wfx_unassign_vif_chanctx,
+	.remain_on_channel       = wfx_remain_on_channel,
+	.cancel_remain_on_channel = wfx_cancel_remain_on_channel,
 };
 
 bool wfx_api_older_than(struct wfx_dev *wdev, int major, int minor)
@@ -289,6 +291,7 @@ struct wfx_dev *wfx_init_common(struct device *dev, const struct wfx_platform_da
 	hw->wiphy->features |= NL80211_FEATURE_AP_SCAN;
 	hw->wiphy->flags |= WIPHY_FLAG_AP_PROBE_RESP_OFFLOAD;
 	hw->wiphy->flags |= WIPHY_FLAG_AP_UAPSD;
+	hw->wiphy->max_remain_on_channel_duration = 5000;
 	hw->wiphy->max_ap_assoc_sta = HIF_LINK_ID_MAX;
 	hw->wiphy->max_scan_ssids = 2;
 	hw->wiphy->max_scan_ie_len = IEEE80211_MAX_DATA_LEN;

drivers/net/wireless/silabs/wfx/scan.c

@@ -145,3 +145,65 @@ void wfx_scan_complete(struct wfx_vif *wvif, int nb_chan_done)
 	wvif->scan_nb_chan_done = nb_chan_done;
 	complete(&wvif->scan_complete);
 }
+
+void wfx_remain_on_channel_work(struct work_struct *work)
+{
+	struct wfx_vif *wvif = container_of(work, struct wfx_vif, remain_on_channel_work);
+	struct ieee80211_channel *chan = wvif->remain_on_channel_chan;
+	int duration = wvif->remain_on_channel_duration;
+	int ret;
+
+	/* Hijack scan request to implement Remain-On-Channel */
+	mutex_lock(&wvif->wdev->conf_mutex);
+	mutex_lock(&wvif->wdev->scan_lock);
+	if (wvif->join_in_progress) {
+		dev_info(wvif->wdev->dev, "abort in-progress REQ_JOIN");
+		wfx_reset(wvif);
+	}
+	wfx_tx_flush(wvif->wdev);
+
+	reinit_completion(&wvif->scan_complete);
+	ret = wfx_hif_scan_uniq(wvif, chan, duration);
+	if (ret)
+		goto end;
+	ieee80211_ready_on_channel(wvif->wdev->hw);
+	ret = wait_for_completion_timeout(&wvif->scan_complete,
+					  msecs_to_jiffies(duration * 120 / 100));
+	if (!ret) {
+		wfx_hif_stop_scan(wvif);
+		ret = wait_for_completion_timeout(&wvif->scan_complete, 1 * HZ);
+		dev_dbg(wvif->wdev->dev, "roc timeout\n");
+	}
+	if (!ret)
+		dev_err(wvif->wdev->dev, "roc didn't stop\n");
+	ieee80211_remain_on_channel_expired(wvif->wdev->hw);
+end:
+	mutex_unlock(&wvif->wdev->scan_lock);
+	mutex_unlock(&wvif->wdev->conf_mutex);
+	wfx_bh_request_tx(wvif->wdev);
+}
+
+int wfx_remain_on_channel(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
+			  struct ieee80211_channel *chan, int duration,
+			  enum ieee80211_roc_type type)
+{
+	struct wfx_dev *wdev = hw->priv;
+	struct wfx_vif *wvif = (struct wfx_vif *)vif->drv_priv;
+
+	if (wfx_api_older_than(wdev, 3, 10))
+		return -EOPNOTSUPP;
+
+	wvif->remain_on_channel_duration = duration;
+	wvif->remain_on_channel_chan = chan;
+	schedule_work(&wvif->remain_on_channel_work);
+	return 0;
+}
+
+int wfx_cancel_remain_on_channel(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
+{
+	struct wfx_vif *wvif = (struct wfx_vif *)vif->drv_priv;
+
+	wfx_hif_stop_scan(wvif);
+	flush_work(&wvif->remain_on_channel_work);
+	return 0;
+}

drivers/net/wireless/silabs/wfx/scan.h

@@ -19,4 +19,10 @@ int wfx_hw_scan(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 void wfx_cancel_hw_scan(struct ieee80211_hw *hw, struct ieee80211_vif *vif);
 void wfx_scan_complete(struct wfx_vif *wvif, int nb_chan_done);
 
+void wfx_remain_on_channel_work(struct work_struct *work);
+int wfx_remain_on_channel(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
+			  struct ieee80211_channel *chan, int duration,
+			  enum ieee80211_roc_type type);
+int wfx_cancel_remain_on_channel(struct ieee80211_hw *hw, struct ieee80211_vif *vif);
+
 #endif

drivers/net/wireless/silabs/wfx/sta.c

@@ -728,6 +728,7 @@ int wfx_add_interface(struct ieee80211_hw *hw, struct ieee80211_vif *vif)
 
 	init_completion(&wvif->scan_complete);
 	INIT_WORK(&wvif->scan_work, wfx_hw_scan_work);
+	INIT_WORK(&wvif->remain_on_channel_work, wfx_remain_on_channel_work);
 
 	wfx_tx_queues_init(wvif);
 	wfx_tx_policy_init(wvif);

drivers/net/wireless/silabs/wfx/wfx.h

@@ -70,6 +70,7 @@ struct wfx_vif {
 
 	bool                       after_dtim_tx_allowed;
 	bool                       join_in_progress;
+	struct completion          set_pm_mode_complete;
 
 	struct delayed_work        beacon_loss_work;
 
@@ -87,7 +88,9 @@ struct wfx_vif {
 	bool                       scan_abort;
 	struct ieee80211_scan_request *scan_req;
 
-	struct completion          set_pm_mode_complete;
+	struct ieee80211_channel   *remain_on_channel_chan;
+	int                        remain_on_channel_duration;
+	struct work_struct         remain_on_channel_work;
 };
 
 static inline struct ieee80211_vif *wvif_to_vif(struct wfx_vif *wvif)