Hi all,
Does anyone know if the 11n standard says that the set of TX rates has to be a subset of the set of RX rates? This seems to be enforced now: when I set up one node to be 2x1, i.e. transmit 2 streams but only able to receive 1, then the mac80211 code only lets it transmit 1 streams (even with a 2-stream-capable receiver at the other end).
A quick diff to net/mac80211/ht.c that fixes this for equal modulation streams is attached; the problem is still there for unequal modulation directly below. Before I send it up I wanted to make sure I'm not crazy.
A second question: my understanding is that if I am a 2x2 node and I associate to a 3x3 AP, the same code will mask out the fact that the AP can receive 3 streams since I can't transmit 3 streams. Is there a way to access this info from the driver if I want it?
Thanks!
Dan
---
From: Daniel Halperin <dhalperi@xxxxxxxxxxxxxxxxx>
Date: Tue, 20 Apr 2010 00:00:29 -0700
Subject: [PATCH] mac80211: support devices with more transmit than receive MCS supported
There is an implicit assumption built into mac80211 that an 11n NIC has a
receive MCS set that contains its TX MCS set, even when
IEEE80211_HT_MCS_TX_RX_DIFF is set. Then, a 2x1 node that can transmit 2
streams but only receive 1 will be unable to transmit 2 streams. Fix this for
equal modulation MCS sets by properly handling the IEEE80211_HT_MCS_TX_RX_DIFF
case.
Signed-off-by: Daniel Halperin <dhalperi@xxxxxxxxxxxxxxxxx>
---
net/mac80211/ht.c | 11 ++++++++---
1 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/net/mac80211/ht.c b/net/mac80211/ht.c
index 2ab106a..249805b 100644
--- a/net/mac80211/ht.c
+++ b/net/mac80211/ht.c
@@ -24,6 +24,7 @@ void ieee80211_ht_cap_ie_to_sta_ht_cap(struct ieee80211_supported_band *sband,
{
u8 ampdu_info, tx_mcs_set_cap;
int i, max_tx_streams;
+ bool use_rx_mask;
BUG_ON(!ht_cap);
@@ -71,12 +72,15 @@ void ieee80211_ht_cap_ie_to_sta_ht_cap(struct ieee80211_supported_band *sband,
return;
/* Counting from 0, therefore +1 */
- if (tx_mcs_set_cap & IEEE80211_HT_MCS_TX_RX_DIFF)
+ if (tx_mcs_set_cap & IEEE80211_HT_MCS_TX_RX_DIFF) {
max_tx_streams =
((tx_mcs_set_cap & IEEE80211_HT_MCS_TX_MAX_STREAMS_MASK)
>> IEEE80211_HT_MCS_TX_MAX_STREAMS_SHIFT) + 1;
- else
+ use_rx_mask = 0;
+ } else {
max_tx_streams = IEEE80211_HT_MCS_TX_MAX_STREAMS;
+ use_rx_mask = 1;
+ }
/*
* 802.11n D5.0 20.3.5 / 20.6 says:
@@ -87,7 +91,8 @@ void ieee80211_ht_cap_ie_to_sta_ht_cap(struct ieee80211_supported_band *sband,
*/
for (i = 0; i < max_tx_streams; i++)
ht_cap->mcs.rx_mask[i] =
- sband->ht_cap.mcs.rx_mask[i] & ht_cap_ie->mcs.rx_mask[i];
+ (use_rx_mask ? sband->ht_cap.mcs.rx_mask[i] : 0xFF) &
+ ht_cap_ie->mcs.rx_mask[i];
if (tx_mcs_set_cap & IEEE80211_HT_MCS_TX_UNEQUAL_MODULATION)
for (i = IEEE80211_HT_MCS_UNEQUAL_MODULATION_START_BYTE;
--
1.5.4.3
--
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