Message-ID: <1336031908.3459.4.camel@jlt3.sipsolutions.net> (sfid-20120503_095834_702323_C18DF261)
Subject: Re: carl9170 - monitor mode TP drop
From: Johannes Berg <johannes@sipsolutions.net>
To: Christian Lamparter <chunkeey@googlemail.com>
Cc: Janusz Dziedzic <janusz.dziedzic@gmail.com>,
	linux-wireless <linux-wireless@vger.kernel.org>
Date: Thu, 03 May 2012 09:58:28 +0200
In-Reply-To: <201204251928.21559.chunkeey@googlemail.com> (sfid-20120425_192840_070867_199F0B3E)
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On Wed, 2012-04-25 at 19:28 +0200, Christian Lamparter wrote:
> On Wednesday, April 25, 2012 07:28:18 AM Janusz Dziedzic wrote:
> > W dniu 23 kwietnia 2012 19:45 użytkownik Christian Lamparter
> > <chunkeey@googlemail.com> napisał:
> > >> This is what I can see on STA1:
> > >> # iperf -c 192.168.254.1 -t 100 -i 5
> > >> [ 3] 10.0-15.0 sec  20.4 MBytes  34.2 Mbits/sec
> > >>
> > >> =====> here I setup carl monitor on second PC, like this:
> > >> =====> iw dev wlan0 set type monitor
> > >> =====> iw dev wlan0 set freq 2437
> > >> =====> ifconfig wlan0 up
> > >>
> > >> [  3] 40.0-45.0 sec  2.38 MBytes  3.98 Mbits/sec
> > > Well, there's the "AR9170_MAC_RX_CTRL_ACK_IN_SNIFFER = bit (30)"
> > > in "AR9170_MAC_REG_RX_CONTROL = (0x1c3c40)".
> > I disabled this in code.
> > 
> > -               rx_ctrl |= AR9170_MAC_RX_CTRL_ACK_IN_SNIFFER;
> > +//             rx_ctrl |= AR9170_MAC_RX_CTRL_ACK_IN_SNIFFER;
> > 
> > After that I don't see any TP drop and can see all packets in
> > wireshark (as expected).
> > 
> > Why carl try to ACK rx packets in monitor mode?
> > Is that a correct behaviour?
> Well, it depends.
> 
> You see without the BIT set, the hardware won't sent any ACKs
> (Not even those which are directed at this interface - which of
> course is also bad, or even worse?) and with the BIT set (and if
> the HW is in Sniffer Mode) then the hardware acks every frames,
> even if they are for a different stations.
> So your fix might break someone else's setup.

You may want to implement the new monitor-mode-vif-to-driver thing in
mac80211 which tells you when you're in *pure* monitor mode.

johannes