net: mac802154: Bring the ability to hold the transmit queue

Create a hold_txs atomic variable and increment/decrement it when
relevant, ie. when we want to hold the queue or release it: currently
all the "stopped" situations are suitable, but very soon we will more
extensively use this feature for MLME purposes.

Upon release, the atomic counter is decremented and checked. If it is
back to 0, then the netif queue gets woken up. This makes the whole
process fully transparent, provided that all the users of
ieee802154_wake/stop_queue() now call ieee802154_hold/release_queue()
instead.

In no situation individual drivers should call any of these helpers
manually in order to avoid messing with the counters. There are other
functions more suited for this purpose which have been introduced, such
as the _xmit_complete() and _xmit_error() helpers which will handle all
that for them.

One advantage is that, as no more drivers call the stop/wake helpers
directly, we can safely stop exporting them and only declare the
hold/release ones in a header only accessible to the core.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20220519150516.443078-6-miquel.raynal@bootlin.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

include/net/cfg802154.h

@@ -11,7 +11,7 @@
 
 #include <linux/ieee802154.h>
 #include <linux/netdevice.h>
-#include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <linux/bug.h>
 
 #include <net/nl802154.h>
@@ -214,8 +214,10 @@ struct wpan_phy {
 	/* the network namespace this phy lives in currently */
 	possible_net_t _net;
 
-	/* Transmission monitoring */
+	/* Transmission monitoring and control */
+	spinlock_t queue_lock;
 	atomic_t ongoing_txs;
+	atomic_t hold_txs;
 
 	char priv[] __aligned(NETDEV_ALIGN);
 };

include/net/mac802154.h

@@ -460,33 +460,6 @@ void ieee802154_unregister_hw(struct ieee802154_hw *hw);
  */
 void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb,
 			   u8 lqi);
-/**
- * ieee802154_wake_queue - wake ieee802154 queue
- * @hw: pointer as obtained from ieee802154_alloc_hw().
- *
- * Tranceivers usually have either one transmit framebuffer or one framebuffer
- * for both transmitting and receiving. Hence, the core currently only handles
- * one frame at a time for each phy, which means we had to stop the queue to
- * avoid new skb to come during the transmission. The queue then needs to be
- * woken up after the operation.
- *
- * Drivers should use this function instead of netif_wake_queue.
- */
-void ieee802154_wake_queue(struct ieee802154_hw *hw);
-
-/**
- * ieee802154_stop_queue - stop ieee802154 queue
- * @hw: pointer as obtained from ieee802154_alloc_hw().
- *
- * Tranceivers usually have either one transmit framebuffer or one framebuffer
- * for both transmitting and receiving. Hence, the core currently only handles
- * one frame at a time for each phy, which means we need to tell upper layers to
- * stop giving us new skbs while we are busy with the transmitted one. The queue
- * must then be stopped before transmitting.
- *
- * Drivers should use this function instead of netif_stop_queue.
- */
-void ieee802154_stop_queue(struct ieee802154_hw *hw);
 
 /**
  * ieee802154_xmit_complete - frame transmission complete

net/ieee802154/core.c

@@ -130,6 +130,8 @@ wpan_phy_new(const struct cfg802154_ops *ops, size_t priv_size)
 
 	init_waitqueue_head(&rdev->dev_wait);
 
+	spin_lock_init(&rdev->wpan_phy.queue_lock);
+
 	return &rdev->wpan_phy;
 }
 EXPORT_SYMBOL(wpan_phy_new);

net/mac802154/cfg.c

@@ -46,7 +46,7 @@ static int ieee802154_suspend(struct wpan_phy *wpan_phy)
 	if (!local->open_count)
 		goto suspend;
 
-	ieee802154_stop_queue(&local->hw);
+	ieee802154_hold_queue(local);
 	synchronize_net();
 
 	/* stop hardware - this must stop RX */
@@ -72,7 +72,7 @@ static int ieee802154_resume(struct wpan_phy *wpan_phy)
 		return ret;
 
 wake_up:
-	ieee802154_wake_queue(&local->hw);
+	ieee802154_release_queue(local);
 	local->suspended = false;
 	return 0;
 }

net/mac802154/ieee802154_i.h

@@ -130,6 +130,25 @@ netdev_tx_t
 ieee802154_subif_start_xmit(struct sk_buff *skb, struct net_device *dev);
 enum hrtimer_restart ieee802154_xmit_ifs_timer(struct hrtimer *timer);
 
+/**
+ * ieee802154_hold_queue - hold ieee802154 queue
+ * @local: main mac object
+ *
+ * Hold a queue by incrementing an atomic counter and requesting the netif
+ * queues to be stopped. The queues cannot be woken up while the counter has not
+ * been reset with as any ieee802154_release_queue() calls as needed.
+ */
+void ieee802154_hold_queue(struct ieee802154_local *local);
+
+/**
+ * ieee802154_release_queue - release ieee802154 queue
+ * @local: main mac object
+ *
+ * Release a queue which is held by decrementing an atomic counter and wake it
+ * up only if the counter reaches 0.
+ */
+void ieee802154_release_queue(struct ieee802154_local *local);
+
 /* MIB callbacks */
 void mac802154_dev_set_page_channel(struct net_device *dev, u8 page, u8 chan);
 

net/mac802154/tx.c

@@ -43,7 +43,7 @@ void ieee802154_xmit_sync_worker(struct work_struct *work)
 
 err_tx:
 	/* Restart the netif queue on each sub_if_data object. */
-	ieee802154_wake_queue(&local->hw);
+	ieee802154_release_queue(local);
 	atomic_dec(&local->phy->ongoing_txs);
 	kfree_skb(skb);
 	netdev_dbg(dev, "transmission failed\n");
@@ -75,7 +75,7 @@ ieee802154_tx(struct ieee802154_local *local, struct sk_buff *skb)
 	}
 
 	/* Stop the netif queue on each sub_if_data object. */
-	ieee802154_stop_queue(&local->hw);
+	ieee802154_hold_queue(local);
 	atomic_inc(&local->phy->ongoing_txs);
 
 	/* Drivers should preferably implement the async callback. In some rare
@@ -99,7 +99,7 @@ ieee802154_tx(struct ieee802154_local *local, struct sk_buff *skb)
 	return NETDEV_TX_OK;
 
 err_wake_netif_queue:
-	ieee802154_wake_queue(&local->hw);
+	ieee802154_release_queue(local);
 	atomic_dec(&local->phy->ongoing_txs);
 err_free_skb:
 	kfree_skb(skb);

net/mac802154/util.c

@@ -13,7 +13,17 @@
 /* privid for wpan_phys to determine whether they belong to us or not */
 const void *const mac802154_wpan_phy_privid = &mac802154_wpan_phy_privid;
 
-void ieee802154_wake_queue(struct ieee802154_hw *hw)
+/**
+ * ieee802154_wake_queue - wake ieee802154 queue
+ * @local: main mac object
+ *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we had to stop the queue to
+ * avoid new skb to come during the transmission. The queue then needs to be
+ * woken up after the operation.
+ */
+static void ieee802154_wake_queue(struct ieee802154_hw *hw)
 {
 	struct ieee802154_local *local = hw_to_local(hw);
 	struct ieee802154_sub_if_data *sdata;
@@ -27,9 +37,18 @@ void ieee802154_wake_queue(struct ieee802154_hw *hw)
 	}
 	rcu_read_unlock();
 }
-EXPORT_SYMBOL(ieee802154_wake_queue);
 
-void ieee802154_stop_queue(struct ieee802154_hw *hw)
+/**
+ * ieee802154_stop_queue - stop ieee802154 queue
+ * @local: main mac object
+ *
+ * Tranceivers usually have either one transmit framebuffer or one framebuffer
+ * for both transmitting and receiving. Hence, the core currently only handles
+ * one frame at a time for each phy, which means we need to tell upper layers to
+ * stop giving us new skbs while we are busy with the transmitted one. The queue
+ * must then be stopped before transmitting.
+ */
+static void ieee802154_stop_queue(struct ieee802154_hw *hw)
 {
 	struct ieee802154_local *local = hw_to_local(hw);
 	struct ieee802154_sub_if_data *sdata;
@@ -43,14 +62,33 @@ void ieee802154_stop_queue(struct ieee802154_hw *hw)
 	}
 	rcu_read_unlock();
 }
-EXPORT_SYMBOL(ieee802154_stop_queue);
+
+void ieee802154_hold_queue(struct ieee802154_local *local)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&local->phy->queue_lock, flags);
+	if (!atomic_fetch_inc(&local->phy->hold_txs))
+		ieee802154_stop_queue(&local->hw);
+	spin_unlock_irqrestore(&local->phy->queue_lock, flags);
+}
+
+void ieee802154_release_queue(struct ieee802154_local *local)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&local->phy->queue_lock, flags);
+	if (!atomic_dec_and_test(&local->phy->hold_txs))
+		ieee802154_wake_queue(&local->hw);
+	spin_unlock_irqrestore(&local->phy->queue_lock, flags);
+}
 
 enum hrtimer_restart ieee802154_xmit_ifs_timer(struct hrtimer *timer)
 {
 	struct ieee802154_local *local =
 		container_of(timer, struct ieee802154_local, ifs_timer);
 
-	ieee802154_wake_queue(&local->hw);
+	ieee802154_release_queue(local);
 
 	return HRTIMER_NORESTART;
 }
@@ -84,7 +122,7 @@ void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb,
 				      hw->phy->sifs_period * NSEC_PER_USEC,
 				      HRTIMER_MODE_REL);
 	} else {
-		ieee802154_wake_queue(hw);
+		ieee802154_release_queue(local);
 	}
 
 	dev_consume_skb_any(skb);
@@ -98,7 +136,7 @@ void ieee802154_xmit_error(struct ieee802154_hw *hw, struct sk_buff *skb,
 	struct ieee802154_local *local = hw_to_local(hw);
 
 	local->tx_result = reason;
-	ieee802154_wake_queue(hw);
+	ieee802154_release_queue(local);
 	dev_kfree_skb_any(skb);
 	atomic_dec(&hw->phy->ongoing_txs);
 }