[PATCH v2 15/18] wifi: mac80211: support antenna control in injection

[gregory.greenman@intel.com]

From: Johannes Berg <johannes.berg@intel.com>

Support antenna control for injection by parsing the antenna
radiotap field (which may be presented multiple times) and
telling the driver about the resulting antenna bitmap. Of
course there's no guarantee the driver will actually honour
this, just like any other injection control.

If misconfigured, i.e. the injected HT/VHT MCS needs more
chains than antennas are configured, the bitmap is reset to
zero, indicating no selection.

For now this is only set up for two anntenas so we keep more
free bits, but that can be trivially extended if any driver
implements support for it that can deal with hardware with
more antennas.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
---
 include/linux/ieee80211.h |  2 ++
 include/net/mac80211.h    |  6 +++++-
 net/mac80211/tx.c         | 14 ++++++++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
index f2965ff3d7c1..3b02f038d509 100644
--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -1705,6 +1705,8 @@ struct ieee80211_mcs_info {
 #define		IEEE80211_HT_MCS_TX_MAX_STREAMS	4
 #define IEEE80211_HT_MCS_TX_UNEQUAL_MODULATION	0x10
 
+#define IEEE80211_HT_MCS_CHAINS(mcs) ((mcs) == 32 ? 1 : (1 + ((mcs) >> 3)))
+
 /*
  * 802.11n D5.0 20.3.5 / 20.6 says:
  * - indices 0 to 7 and 32 are single spatial stream
diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index b3df8cb2919b..b67583ddae9c 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -1178,7 +1178,11 @@ struct ieee80211_tx_info {
 					u8 use_cts_prot:1;
 					u8 short_preamble:1;
 					u8 skip_table:1;
-					/* 2 bytes free */
+
+					/* for injection only (bitmap) */
+					u8 antennas:2;
+
+					/* 14 bits free */
 				};
 				/* only needed before rate control */
 				unsigned long jiffies;
diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 932516f8cc13..a984fc54644e 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -2162,6 +2162,11 @@ bool ieee80211_parse_tx_radiotap(struct sk_buff *skb,
 			rate_found = true;
 			break;
 
+		case IEEE80211_RADIOTAP_ANTENNA:
+			/* this can appear multiple times, keep a bitmap */
+			info->control.antennas |= BIT(*iterator.this_arg);
+			break;
+
 		case IEEE80211_RADIOTAP_DATA_RETRIES:
 			rate_retries = *iterator.this_arg;
 			break;
@@ -2256,8 +2261,17 @@ bool ieee80211_parse_tx_radiotap(struct sk_buff *skb,
 		}
 
 		if (rate_flags & IEEE80211_TX_RC_MCS) {
+			/* reset antennas if not enough */
+			if (IEEE80211_HT_MCS_CHAINS(rate) >
+					hweight8(info->control.antennas))
+				info->control.antennas = 0;
+
 			info->control.rates[0].idx = rate;
 		} else if (rate_flags & IEEE80211_TX_RC_VHT_MCS) {
+			/* reset antennas if not enough */
+			if (vht_nss > hweight8(info->control.antennas))
+				info->control.antennas = 0;
+
 			ieee80211_rate_set_vht(info->control.rates, vht_mcs,
 					       vht_nss);
 		} else if (sband) {
-- 
2.38.1