mac80211: add STBC flag for radiotap

Some chips can tell us if received frame was
encoded with STBC or not. To make this information available
in user space we can use updated radiotap specification:
http://www.radiotap.org/defined-fields/MCS

This patch will set number of STBC encoded spatial streams (Nss).
The HAVE_STBC flag should be provided by driver.

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

include/net/ieee80211_radiotap.h

@@ -269,6 +269,7 @@ enum ieee80211_radiotap_type {
 #define IEEE80211_RADIOTAP_MCS_HAVE_GI		0x04
 #define IEEE80211_RADIOTAP_MCS_HAVE_FMT		0x08
 #define IEEE80211_RADIOTAP_MCS_HAVE_FEC		0x10
+#define IEEE80211_RADIOTAP_MCS_HAVE_STBC	0x20
 
 #define IEEE80211_RADIOTAP_MCS_BW_MASK		0x03
 #define		IEEE80211_RADIOTAP_MCS_BW_20	0
@@ -278,6 +279,12 @@ enum ieee80211_radiotap_type {
 #define IEEE80211_RADIOTAP_MCS_SGI		0x04
 #define IEEE80211_RADIOTAP_MCS_FMT_GF		0x08
 #define IEEE80211_RADIOTAP_MCS_FEC_LDPC		0x10
+#define IEEE80211_RADIOTAP_MCS_STBC_MASK	0x60
+#define		IEEE80211_RADIOTAP_MCS_STBC_1	1
+#define		IEEE80211_RADIOTAP_MCS_STBC_2	2
+#define		IEEE80211_RADIOTAP_MCS_STBC_3	3
+
+#define IEEE80211_RADIOTAP_MCS_STBC_SHIFT	5
 
 /* For IEEE80211_RADIOTAP_AMPDU_STATUS */
 #define IEEE80211_RADIOTAP_AMPDU_REPORT_ZEROLEN		0x0001

include/net/mac80211.h

@@ -805,6 +805,7 @@ ieee80211_tx_info_clear_status(struct ieee80211_tx_info *info)
  *	on this subframe
  * @RX_FLAG_AMPDU_DELIM_CRC_KNOWN: The delimiter CRC field is known (the CRC
  *	is stored in the @ampdu_delimiter_crc field)
+ * @RX_FLAG_STBC_MASK: STBC 2 bit bitmask. 1 - Nss=1, 2 - Nss=2, 3 - Nss=3
  */
 enum mac80211_rx_flags {
 	RX_FLAG_MMIC_ERROR		= BIT(0),
@@ -832,8 +833,11 @@ enum mac80211_rx_flags {
 	RX_FLAG_80MHZ			= BIT(23),
 	RX_FLAG_80P80MHZ		= BIT(24),
 	RX_FLAG_160MHZ			= BIT(25),
+	RX_FLAG_STBC_MASK		= BIT(26) | BIT(27),
 };
 
+#define RX_FLAG_STBC_SHIFT		26
+
 /**
  * struct ieee80211_rx_status - receive status
  *

net/mac80211/rx.c

@@ -258,6 +258,8 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 	pos += 2;
 
 	if (status->flag & RX_FLAG_HT) {
+		unsigned int stbc;
+
 		rthdr->it_present |= cpu_to_le32(1 << IEEE80211_RADIOTAP_MCS);
 		*pos++ = local->hw.radiotap_mcs_details;
 		*pos = 0;
@@ -267,6 +269,8 @@ ieee80211_add_rx_radiotap_header(struct ieee80211_local *local,
 			*pos |= IEEE80211_RADIOTAP_MCS_BW_40;
 		if (status->flag & RX_FLAG_HT_GF)
 			*pos |= IEEE80211_RADIOTAP_MCS_FMT_GF;
+		stbc = (status->flag & RX_FLAG_STBC_MASK) >> RX_FLAG_STBC_SHIFT;
+		*pos |= stbc << IEEE80211_RADIOTAP_MCS_STBC_SHIFT;
 		pos++;
 		*pos++ = status->rate_idx;
 	}