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>

diff --git a/drivers/net/wireless/ath/carl9170/mac.c b/drivers/net/wireless/ath/carl9170/mac.c
index e3b1b6e..24d75ab 100644 (file)
--- 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;
        }