carl9170: fix spurious transmissions in sniffer mode

Several people have complained about an unusual
and undocumented feature of the AR9170 hardware:

In siffer mode, the hardware generates spurious
ACK frames for every received frame... even
broadcasts.

The reason for this malfunction is unknown:
<http://marc.info/?l=linux-wireless&m=134517238506033>
But there's a workaround: Instead of the special
sniffer mode, the hardware will be put into
station mode and all rx filters are disabled.

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reported-by: Marco Fonseca <marco@tampabay.rr.com>
Reported-by: Janusz Dziedzic <janusz.dziedzic@gmail.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 18 insertions, 3 deletions

diff --git a/drivers/net/wireless/ath/carl9170/mac.c b/drivers/net/wireless/ath/carl9170/mac.c
index e3b1b6e87760..24d75ab94f0d 100644
--- a/drivers/net/wireless/ath/carl9170/mac.c
+++ b/drivers/net/wireless/ath/carl9170/mac.c
@@ -343,7 +343,24 @@ int carl9170_set_operating_mode(struct ar9170 *ar)
                         break;
                 }
         } else {
-                mac_addr = NULL;
+                /*
+                 * Enable monitor mode
+                 *
+                 * rx_ctrl |= AR9170_MAC_RX_CTRL_ACK_IN_SNIFFER;
+                 * sniffer |= AR9170_MAC_SNIFFER_ENABLE_PROMISC;
+                 *
+                 * When the hardware is in SNIFFER_PROMISC mode,
+                 * it generates spurious ACKs for every incoming
+                 * frame. This confuses every peer in the
+                 * vicinity and the network throughput will suffer
+                 * badly.
+                 *
+                 * Hence, the hardware will be put into station
+                 * mode and just the rx filters are disabled.
+                 */
+                cam_mode |= AR9170_MAC_CAM_STA;
+                rx_ctrl |= AR9170_MAC_RX_CTRL_PASS_TO_HOST;
+                mac_addr = common->macaddr;
                 bssid = NULL;
         }
         rcu_read_unlock();
@@ -355,8 +372,6 @@ int carl9170_set_operating_mode(struct ar9170 *ar)
                 enc_mode |= AR9170_MAC_ENCRYPTION_RX_SOFTWARE;
 
         if (ar->sniffer_enabled) {
-                rx_ctrl |= AR9170_MAC_RX_CTRL_ACK_IN_SNIFFER;
-                sniffer |= AR9170_MAC_SNIFFER_ENABLE_PROMISC;
                 enc_mode |= AR9170_MAC_ENCRYPTION_RX_SOFTWARE;
         }