mac80211: Add TXQ scheduling API

This adds an API to mac80211 to handle scheduling of TXQs. The interface
between driver and mac80211 for TXQ handling is changed by adding two new
functions: ieee80211_next_txq(), which will return the next TXQ to schedule
in the current round-robin rotation, and ieee80211_return_txq(), which the
driver uses to indicate that it has finished scheduling a TXQ (which will
then be put back in the scheduling rotation if it isn't empty).

The driver must call ieee80211_txq_schedule_start() at the start of each
scheduling session, and ieee80211_txq_schedule_end() at the end. The API
then guarantees that the same TXQ is not returned twice in the same
session (so a driver can loop on ieee80211_next_txq() without worrying
about breaking the loop.

Usage of the new API is optional, so drivers can be ported one at a time.
In this patch, the actual scheduling performed by mac80211 is simple
round-robin, but a subsequent commit adds airtime fairness awareness to the
scheduler.

Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
[minor kernel-doc fix, propagate sparse locking checks out]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 59 insertions, 4 deletions

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 88219cc137c3..e8a057f071c4 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -108,9 +108,15 @@
  * The driver is expected to initialize its private per-queue data for stations
  * and interfaces in the .add_interface and .sta_add ops.
  *
- * The driver can't access the queue directly. To dequeue a frame, it calls
- * ieee80211_tx_dequeue(). Whenever mac80211 adds a new frame to a queue, it
- * calls the .wake_tx_queue driver op.
+ * The driver can't access the queue directly. To dequeue a frame from a
+ * txq, it calls ieee80211_tx_dequeue(). Whenever mac80211 adds a new frame to a
+ * queue, it calls the .wake_tx_queue driver op.
+ *
+ * Drivers can optionally delegate responsibility for scheduling queues to
+ * mac80211, to take advantage of airtime fairness accounting. In this case, to
+ * obtain the next queue to pull frames from, the driver calls
+ * ieee80211_next_txq(). The driver is then expected to return the txq using
+ * ieee80211_return_txq().
  *
  * For AP powersave TIM handling, the driver only needs to indicate if it has
  * buffered packets in the driver specific data structures by calling
@@ -6103,7 +6109,8 @@ void ieee80211_unreserve_tid(struct ieee80211_sta *sta, u8 tid);
  * ieee80211_tx_dequeue - dequeue a packet from a software tx queue
  *
  * @hw: pointer as obtained from ieee80211_alloc_hw()
- * @txq: pointer obtained from station or virtual interface
+ * @txq: pointer obtained from station or virtual interface, or from
+ *	ieee80211_next_txq()
  *
  * Returns the skb if successful, %NULL if no frame was available.
  *
@@ -6119,6 +6126,54 @@ struct sk_buff *ieee80211_tx_dequeue(struct ieee80211_hw *hw,
 				     struct ieee80211_txq *txq);
 
 /**
+ * ieee80211_next_txq - get next tx queue to pull packets from
+ *
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @ac: AC number to return packets from.
+ *
+ * Should only be called between calls to ieee80211_txq_schedule_start()
+ * and ieee80211_txq_schedule_end().
+ * Returns the next txq if successful, %NULL if no queue is eligible. If a txq
+ * is returned, it should be returned with ieee80211_return_txq() after the
+ * driver has finished scheduling it.
+ */
+struct ieee80211_txq *ieee80211_next_txq(struct ieee80211_hw *hw, u8 ac);
+
+/**
+ * ieee80211_return_txq - return a TXQ previously acquired by ieee80211_next_txq()
+ *
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @txq: pointer obtained from station or virtual interface
+ *
+ * Should only be called between calls to ieee80211_txq_schedule_start()
+ * and ieee80211_txq_schedule_end().
+ */
+void ieee80211_return_txq(struct ieee80211_hw *hw, struct ieee80211_txq *txq);
+
+/**
+ * ieee80211_txq_schedule_start - acquire locks for safe scheduling of an AC
+ *
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @ac: AC number to acquire locks for
+ *
+ * Acquire locks needed to schedule TXQs from the given AC. Should be called
+ * before ieee80211_next_txq() or ieee80211_return_txq().
+ */
+void ieee80211_txq_schedule_start(struct ieee80211_hw *hw, u8 ac)
+	__acquires(txq_lock);
+
+/**
+ * ieee80211_txq_schedule_end - release locks for safe scheduling of an AC
+ *
+ * @hw: pointer as obtained from ieee80211_alloc_hw()
+ * @ac: AC number to acquire locks for
+ *
+ * Release locks previously acquired by ieee80211_txq_schedule_end().
+ */
+void ieee80211_txq_schedule_end(struct ieee80211_hw *hw, u8 ac)
+	__releases(txq_lock);
+
+/**
  * ieee80211_txq_get_depth - get pending frame/byte count of given txq
  *
  * The values are not guaranteed to be coherent with regard to each other, i.e.