Dan, I apologise for the late reply. > I'm trying to track down an anomaly with a 3-stream 802.11n AP. > iwlwifi is saying that a single antenna should be sufficient even when > the AP supports 3 streams. Here's what I've tracked down: > Code in iwl-agn-rxon.c uses the ht_cap TX MCS parameters to determine > how many streams the other side supports: > <http://git.kernel.org/?p=linux/kernel/git/iwlwifi/iwlwifi-2.6.git;a=blob;f=drivers/net/wireless/iwlwifi/iwl-agn-rxon.c;h=d33e4db7e56cab88abc3281d04adf32162b8020e;hb=HEAD#l470> > Yet, it looks like mac80211 doesn't actually set those variables at > all! In net/mac80211/ht.c, when converting the IE to the Station HT > cap: > <http://git.kernel.org/?p=linux/kernel/git/iwlwifi/iwlwifi-2.6.git;a=blob;f=net/mac80211/ht.c;h=75d679d75e63e92143d55a47601a1dfc1377ba03;hb=HEAD#l21> > we first zero out the HT CAP (line 30) and then never actually set the > ht_cap->mcs.tx_params variables at all. Grep says that's the only use > of mcs.tx_params in that directory, so I'm pretty confident mac80211 > just never does that. Thus iwlwifi thinks it only needs to have 1 RX > antenna enabled (though it defaults to a minimum of 2 when possible) > and basically fails to receive 3 stream packets. > Is this a bug in iwlwifi or mac80211? Did you ever try to set it in mac80211, like say the below change? I think that'd be the minimal fix that can be backported easily too. johannes --- wireless-testing.orig/net/mac80211/ht.c 2011-01-28 15:03:29.000000000 +0100 +++ wireless-testing/net/mac80211/ht.c 2011-01-28 15:32:14.000000000 +0100 @@ -66,6 +66,14 @@ void ieee80211_ht_cap_ie_to_sta_ht_cap(s /* own MCS TX capabilities */ tx_mcs_set_cap = sband->ht_cap.mcs.tx_params; + /* + * peer MCS TX capabilities + * + * TODO: - restrict # of streams to our RX? + * - clear uneq modulation if we can't RX it? + */ + ht_cap->mcs.tx_params = ht_cap_ie->mcs.tx_params; + /* can we TX with MCS rates? */ if (!(tx_mcs_set_cap & IEEE80211_HT_MCS_TX_DEFINED)) return; @@ -79,7 +87,7 @@ void ieee80211_ht_cap_ie_to_sta_ht_cap(s max_tx_streams = IEEE80211_HT_MCS_TX_MAX_STREAMS; /* - * 802.11n D5.0 20.3.5 / 20.6 says: + * 802.11n-2009 20.3.5 / 20.6 says: * - indices 0 to 7 and 32 are single spatial stream * - 8 to 31 are multiple spatial streams using equal modulation * [8..15 for two streams, 16..23 for three and 24..31 for four] -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
