mac80211: update aggregation documentation

Even before the recent changes, the documentation
for TX aggregation was somewhat out of date. Update
it and also add documentation for the RX side.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/agg-rx.c

@@ -13,6 +13,29 @@
  * published by the Free Software Foundation.
  */
 
+/**
+ * DOC: RX A-MPDU aggregation
+ *
+ * Aggregation on the RX side requires only implementing the
+ * @ampdu_action callback that is invoked to start/stop any
+ * block-ack sessions for RX aggregation.
+ *
+ * When RX aggregation is started by the peer, the driver is
+ * notified via @ampdu_action function, with the
+ * %IEEE80211_AMPDU_RX_START action, and may reject the request
+ * in which case a negative response is sent to the peer, if it
+ * accepts it a positive response is sent.
+ *
+ * While the session is active, the device/driver are required
+ * to de-aggregate frames and pass them up one by one to mac80211,
+ * which will handle the reorder buffer.
+ *
+ * When the aggregation session is stopped again by the peer or
+ * ourselves, the driver's @ampdu_action function will be called
+ * with the action %IEEE80211_AMPDU_RX_STOP. In this case, the
+ * call must not fail.
+ */
+
 #include <linux/ieee80211.h>
 #include <linux/slab.h>
 #include <net/mac80211.h>

net/mac80211/agg-tx.c

@@ -21,28 +21,39 @@
 #include "wme.h"
 
 /**
- * DOC: TX aggregation
+ * DOC: TX A-MPDU aggregation
  *
  * Aggregation on the TX side requires setting the hardware flag
- * %IEEE80211_HW_AMPDU_AGGREGATION as well as, if present, the @ampdu_queues
- * hardware parameter to the number of hardware AMPDU queues. If there are no
- * hardware queues then the driver will (currently) have to do all frame
- * buffering.
+ * %IEEE80211_HW_AMPDU_AGGREGATION. The driver will then be handed
+ * packets with a flag indicating A-MPDU aggregation. The driver
+ * or device is responsible for actually aggregating the frames,
+ * as well as deciding how many and which to aggregate.
  *
- * When TX aggregation is started by some subsystem (usually the rate control
- * algorithm would be appropriate) by calling the
- * ieee80211_start_tx_ba_session() function, the driver will be notified via
- * its @ampdu_action function, with the %IEEE80211_AMPDU_TX_START action.
+ * When TX aggregation is started by some subsystem (usually the rate
+ * control algorithm would be appropriate) by calling the
+ * ieee80211_start_tx_ba_session() function, the driver will be
+ * notified via its @ampdu_action function, with the
+ * %IEEE80211_AMPDU_TX_START action.
  *
  * In response to that, the driver is later required to call the
- * ieee80211_start_tx_ba_cb() (or ieee80211_start_tx_ba_cb_irqsafe())
- * function, which will start the aggregation session.
+ * ieee80211_start_tx_ba_cb_irqsafe() function, which will really
+ * start the aggregation session after the peer has also responded.
+ * If the peer responds negatively, the session will be stopped
+ * again right away. Note that it is possible for the aggregation
+ * session to be stopped before the driver has indicated that it
+ * is done setting it up, in which case it must not indicate the
+ * setup completion.
  *
- * Similarly, when the aggregation session is stopped by
- * ieee80211_stop_tx_ba_session(), the driver's @ampdu_action function will
- * be called with the action %IEEE80211_AMPDU_TX_STOP. In this case, the
- * call must not fail, and the driver must later call ieee80211_stop_tx_ba_cb()
- * (or ieee80211_stop_tx_ba_cb_irqsafe()).
+ * Also note that, since we also need to wait for a response from
+ * the peer, the driver is notified of the completion of the
+ * handshake by the %IEEE80211_AMPDU_TX_OPERATIONAL action to the
+ * @ampdu_action callback.
+ *
+ * Similarly, when the aggregation session is stopped by the peer
+ * or something calling ieee80211_stop_tx_ba_session(), the driver's
+ * @ampdu_action function will be called with the action
+ * %IEEE80211_AMPDU_TX_STOP. In this case, the call must not fail,
+ * and the driver must later call ieee80211_stop_tx_ba_cb_irqsafe().
  */
 
 static void ieee80211_send_addba_request(struct ieee80211_sub_if_data *sdata,