[RFC/RFT] ath9k_htc: avoid scheduling while atomic on sta_rc_update

[Stanislaw Gruszka <sgruszka@redhat.com>]

mac80211 ->sta_rc_update() callback must be atomic. Since we have to
take mutex and do other operations that can sleep when sending fimrware
commands to device, the only option to satisfy atomicity requirement of
->sta_rc_update(), that I can see, is introduce work_struct and defer
uploading new rates to that work.

I don't have h/w to test this patch. Since sta_rc_update() calls are
very unlikely, those who would like to test that patch should remove
my previous patch "ath9k_htc: make ->sta_rc_update atomic for most
calls" and possibly even modify mac80211 to call sta_rc_update(),
without actual reason, just to test changed ath9k_htc code.

Thanks
Stanislaw
---
 drivers/net/wireless/ath/ath9k/htc.h          |  2 +
 drivers/net/wireless/ath/ath9k/htc_drv_main.c | 60 +++++++++++++++++----------
 2 files changed, 40 insertions(+), 22 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/htc.h b/drivers/net/wireless/ath/ath9k/htc.h
index 58da346..99a2031 100644
--- a/drivers/net/wireless/ath/ath9k/htc.h
+++ b/drivers/net/wireless/ath/ath9k/htc.h
@@ -262,6 +262,8 @@ enum tid_aggr_state {
 struct ath9k_htc_sta {
 	u8 index;
 	enum tid_aggr_state tid_state[ATH9K_HTC_MAX_TID];
+	struct work_struct rc_update_work;
+	struct ath9k_htc_priv *htc_priv;
 };
 
 #define ATH9K_HTC_RXBUF 256
diff --git a/drivers/net/wireless/ath/ath9k/htc_drv_main.c b/drivers/net/wireless/ath/ath9k/htc_drv_main.c
index a57af9b..c9254a6 100644
--- a/drivers/net/wireless/ath/ath9k/htc_drv_main.c
+++ b/drivers/net/wireless/ath/ath9k/htc_drv_main.c
@@ -1270,18 +1270,50 @@ static void ath9k_htc_configure_filter(struct ieee80211_hw *hw,
 	mutex_unlock(&priv->mutex);
 }
 
+static void ath9k_htc_sta_rc_update_work(struct work_struct *work)
+{
+	struct ath9k_htc_sta *ista =
+	    container_of(work, struct ath9k_htc_sta, rc_update_work);
+	struct ieee80211_sta *sta =
+	    container_of((void *)ista, struct ieee80211_sta, drv_priv);
+	struct ath9k_htc_priv *priv = ista->htc_priv;
+	struct ath_common *common = ath9k_hw_common(priv->ah);
+	struct ath9k_htc_target_rate trate;
+
+	mutex_lock(&priv->mutex);
+	ath9k_htc_ps_wakeup(priv);
+
+	memset(&trate, 0, sizeof(struct ath9k_htc_target_rate));
+	ath9k_htc_setup_rate(priv, sta, &trate);
+	if (!ath9k_htc_send_rate_cmd(priv, &trate))
+		ath_dbg(common, CONFIG,
+			"Supported rates for sta: %pM updated, rate caps: 0x%X\n",
+			sta->addr, be32_to_cpu(trate.capflags));
+	else
+		ath_dbg(common, CONFIG,
+			"Unable to update supported rates for sta: %pM\n",
+			sta->addr);
+
+	ath9k_htc_ps_restore(priv);
+	mutex_unlock(&priv->mutex);
+}
+
 static int ath9k_htc_sta_add(struct ieee80211_hw *hw,
 			     struct ieee80211_vif *vif,
 			     struct ieee80211_sta *sta)
 {
 	struct ath9k_htc_priv *priv = hw->priv;
+	struct ath9k_htc_sta *ista = (struct ath9k_htc_sta *) sta->drv_priv;
 	int ret;
 
 	mutex_lock(&priv->mutex);
 	ath9k_htc_ps_wakeup(priv);
 	ret = ath9k_htc_add_station(priv, vif, sta);
-	if (!ret)
+	if (!ret) {
+		INIT_WORK(&ista->rc_update_work, ath9k_htc_sta_rc_update_work);
+		ista->htc_priv = priv;
 		ath9k_htc_init_rate(priv, sta);
+	}
 	ath9k_htc_ps_restore(priv);
 	mutex_unlock(&priv->mutex);
 
@@ -1293,12 +1325,13 @@ static int ath9k_htc_sta_remove(struct ieee80211_hw *hw,
 				struct ieee80211_sta *sta)
 {
 	struct ath9k_htc_priv *priv = hw->priv;
-	struct ath9k_htc_sta *ista;
+	struct ath9k_htc_sta *ista = (struct ath9k_htc_sta *) sta->drv_priv;
 	int ret;
 
+	cancel_work_sync(&ista->rc_update_work);
+
 	mutex_lock(&priv->mutex);
 	ath9k_htc_ps_wakeup(priv);
-	ista = (struct ath9k_htc_sta *) sta->drv_priv;
 	htc_sta_drain(priv->htc, ista->index);
 	ret = ath9k_htc_remove_station(priv, vif, sta);
 	ath9k_htc_ps_restore(priv);
@@ -1311,29 +1344,12 @@ static void ath9k_htc_sta_rc_update(struct ieee80211_hw *hw,
 				    struct ieee80211_vif *vif,
 				    struct ieee80211_sta *sta, u32 changed)
 {
-	struct ath9k_htc_priv *priv = hw->priv;
-	struct ath_common *common = ath9k_hw_common(priv->ah);
-	struct ath9k_htc_target_rate trate;
+	struct ath9k_htc_sta *ista = (struct ath9k_htc_sta *) sta->drv_priv;
 
 	if (!(changed & IEEE80211_RC_SUPP_RATES_CHANGED))
 		return;
 
-	mutex_lock(&priv->mutex);
-	ath9k_htc_ps_wakeup(priv);
-
-	memset(&trate, 0, sizeof(struct ath9k_htc_target_rate));
-	ath9k_htc_setup_rate(priv, sta, &trate);
-	if (!ath9k_htc_send_rate_cmd(priv, &trate))
-		ath_dbg(common, CONFIG,
-			"Supported rates for sta: %pM updated, rate caps: 0x%X\n",
-			sta->addr, be32_to_cpu(trate.capflags));
-	else
-		ath_dbg(common, CONFIG,
-			"Unable to update supported rates for sta: %pM\n",
-			sta->addr);
-
-	ath9k_htc_ps_restore(priv);
-	mutex_unlock(&priv->mutex);
+	schedule_work(&ista->rc_update_work);
 }
 
 static int ath9k_htc_conf_tx(struct ieee80211_hw *hw,
-- 
1.7.11.7