mac80211: support reporting A-MSDU subframes individually

Some devices may not be able to report A-MSDUs in
single buffers. Drivers for such devices were
forced to re-assemble A-MSDUs which would then
be eventually disassembled by mac80211. This could
lead to CPU cache thrashing and poor performance.

Since A-MSDU has a single sequence number all
subframes share it. This was in conflict with
retransmission/duplication recovery
(IEEE802.11-2012: 9.3.2.10).

Patch introduces a new flag that is meant to be
set for all individually reported A-MSDU subframes
except the last one. This ensures the
last_seq_ctrl is updated after the last subframe
is processed. If an A-MSDU is actually a duplicate
transmission all reported subframes will be
properly discarded.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
[johannes: add braces that were missing even before]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 8cff800..da80119 100644 (file)
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -829,6 +829,15 @@ ieee80211_tx_info_clear_status(struct ieee80211_tx_info *info)
  * @RX_FLAG_STBC_MASK: STBC 2 bit bitmask. 1 - Nss=1, 2 - Nss=2, 3 - Nss=3
  * @RX_FLAG_10MHZ: 10 MHz (half channel) was used
  * @RX_FLAG_5MHZ: 5 MHz (quarter channel) was used
+ * @RX_FLAG_AMSDU_MORE: Some drivers may prefer to report separate A-MSDU
+ *     subframes instead of a one huge frame for performance reasons.
+ *     All, but the last MSDU from an A-MSDU should have this flag set. E.g.
+ *     if an A-MSDU has 3 frames, the first 2 must have the flag set, while
+ *     the 3rd (last) one must not have this flag set. The flag is used to
+ *     deal with retransmission/duplication recovery properly since A-MSDU
+ *     subframes share the same sequence number. Reported subframes can be
+ *     either regular MSDU or singly A-MSDUs. Subframes must not be
+ *     interleaved with other frames.
  */
 enum mac80211_rx_flags {
        RX_FLAG_MMIC_ERROR              = BIT(0),
@@ -859,6 +868,7 @@ enum mac80211_rx_flags {
        RX_FLAG_STBC_MASK               = BIT(26) | BIT(27),
        RX_FLAG_10MHZ                   = BIT(28),
        RX_FLAG_5MHZ                    = BIT(29),
+       RX_FLAG_AMSDU_MORE              = BIT(30),
 };
 
 #define RX_FLAG_STBC_SHIFT             26

diff --git a/net/mac80211/rx.c b/net/mac80211/rx.c
index 8e908e1..f0247a4 100644 (file)
--- a/net/mac80211/rx.c
+++ b/net/mac80211/rx.c
@@ -995,8 +995,9 @@ ieee80211_rx_h_check(struct ieee80211_rx_data *rx)
                                rx->sta->num_duplicates++;
                        }
                        return RX_DROP_UNUSABLE;
-               } else
+               } else if (!(status->flag & RX_FLAG_AMSDU_MORE)) {
                        rx->sta->last_seq_ctrl[rx->seqno_idx] = hdr->seq_ctrl;
+               }
        }
 
        if (unlikely(rx->skb->len < 16)) {