[RFC v2 3/7] ieee80211: add new VHT capability fields/parsing

[Johannes Berg <johannes@sipsolutions.net>]

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

IEEE 802.11-2016 extended the VHT capability fields to allow
indicating the number of spatial streams depending on the
actually used bandwidth, add support for decoding this.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/linux/ieee80211.h | 105 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 103 insertions(+), 2 deletions(-)

diff --git a/include/linux/ieee80211.h b/include/linux/ieee80211.h
index 4a7200c6c9ea..c51d309a45e7 100644
--- a/include/linux/ieee80211.h
+++ b/include/linux/ieee80211.h
@@ -1457,13 +1457,16 @@ struct ieee80211_ht_operation {
  *	STA can receive. Rate expressed in units of 1 Mbps.
  *	If this field is 0 this value should not be used to
  *	consider the highest RX data rate supported.
- *	The top 3 bits of this field are reserved.
+ *	The top 3 bits of this field indicate the Maximum NSTS,total
+ *	(a beamformee capability.)
  * @tx_mcs_map: TX MCS map 2 bits for each stream, total 8 streams
  * @tx_highest: Indicates highest long GI VHT PPDU data rate
  *	STA can transmit. Rate expressed in units of 1 Mbps.
  *	If this field is 0 this value should not be used to
  *	consider the highest TX data rate supported.
- *	The top 3 bits of this field are reserved.
+ *	The top 2 bits of this field are reserved, the
+ *	3rd bit from the top indiciates VHT Extended NSS BW
+ *	Capability.
  */
 struct ieee80211_vht_mcs_info {
 	__le16 rx_mcs_map;
@@ -1472,6 +1475,13 @@ struct ieee80211_vht_mcs_info {
 	__le16 tx_highest;
 } __packed;
 
+/* for rx_highest */
+#define IEEE80211_VHT_MAX_NSTS_TOTAL_SHIFT	13
+#define IEEE80211_VHT_MAX_NSTS_TOTAL_MASK	(7 << IEEE80211_VHT_MAX_NSTS_TOTAL_SHIFT)
+
+/* for tx_highest */
+#define IEEE80211_VHT_EXT_NSS_BW_CAPABLE	(1 << 13)
+
 /**
  * enum ieee80211_vht_mcs_support - VHT MCS support definitions
  * @IEEE80211_VHT_MCS_SUPPORT_0_7: MCSes 0-7 are supported for the
@@ -1547,6 +1557,7 @@ struct ieee80211_vht_operation {
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160MHZ		0x00000004
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_160_80PLUS80MHZ	0x00000008
 #define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK			0x0000000C
+#define IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT			2
 #define IEEE80211_VHT_CAP_RXLDPC				0x00000010
 #define IEEE80211_VHT_CAP_SHORT_GI_80				0x00000020
 #define IEEE80211_VHT_CAP_SHORT_GI_160				0x00000040
@@ -1575,6 +1586,96 @@ struct ieee80211_vht_operation {
 #define IEEE80211_VHT_CAP_VHT_LINK_ADAPTATION_VHT_MRQ_MFB	0x0c000000
 #define IEEE80211_VHT_CAP_RX_ANTENNA_PATTERN			0x10000000
 #define IEEE80211_VHT_CAP_TX_ANTENNA_PATTERN			0x20000000
+#define IEEE80211_VHT_CAP_EXT_NSS_BW_SHIFT			30
+#define IEEE80211_VHT_CAP_EXT_NSS_BW_MASK			0xc0000000
+
+static int __maybe_unused
+ieee80211_get_vht_max_nss(struct ieee80211_vht_cap *cap,
+			  enum ieee80211_vht_chanwidth bw,
+			  int mcs)
+{
+	u16 map = le16_to_cpu(cap->supp_mcs.rx_mcs_map);
+	int max_vht_nss;
+	int ext_nss_bw;
+	int supp_width;
+	int i, mcs_encoding;
+
+	if (map == 0xffff)
+		return 0;
+
+	if (WARN_ON(mcs > 9))
+		return 0;
+	if (mcs <= 7)
+		mcs_encoding = 0;
+	else if (mcs == 8)
+		mcs_encoding = 1;
+	else
+		mcs_encoding = 2;
+
+	/* find max_vht_nss for the given MCS */
+	for (i = 7; i >= 0; i--) {
+		int supp = (map >> (2*i)) & 3;
+
+		if (supp == 3)
+			continue;
+
+		if (supp >= mcs_encoding) {
+			max_vht_nss = i;
+			break;
+		}
+	}
+
+	if (!(cap->supp_mcs.tx_mcs_map & cpu_to_le16(IEEE80211_VHT_EXT_NSS_BW_CAPABLE)))
+		return max_vht_nss;
+
+	ext_nss_bw = (le32_to_cpu(cap->vht_cap_info) &
+					IEEE80211_VHT_CAP_EXT_NSS_BW_MASK)
+			>> IEEE80211_VHT_CAP_EXT_NSS_BW_SHIFT;
+	supp_width = (le32_to_cpu(cap->vht_cap_info) &
+					IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_MASK)
+			>> IEEE80211_VHT_CAP_SUPP_CHAN_WIDTH_SHIFT;
+
+	/*
+	 * Cover all the special cases according to IEEE 802.11-2016 Table 9-250.
+	 * All other cases are either factor of 1 or not valid/supported.
+	 */
+	switch (bw) {
+	case IEEE80211_VHT_CHANWIDTH_USE_HT:
+	case IEEE80211_VHT_CHANWIDTH_80MHZ:
+		if ((supp_width == 1 || supp_width == 2) &&
+		    ext_nss_bw == 3)
+			return 2 * max_vht_nss;
+		break;
+	case IEEE80211_VHT_CHANWIDTH_160MHZ:
+		if (supp_width == 0 &&
+		    (ext_nss_bw == 1 || ext_nss_bw == 2))
+			return DIV_ROUND_UP(max_vht_nss, 2);
+		if (supp_width == 0 &&
+		    ext_nss_bw == 3)
+			return DIV_ROUND_UP(3 * max_vht_nss, 4);
+		if (supp_width == 1 &&
+		    ext_nss_bw == 3)
+			return 2 * max_vht_nss;
+		break;
+	case IEEE80211_VHT_CHANWIDTH_80P80MHZ:
+		if (supp_width == 0 &&
+		    ext_nss_bw == 2)
+			return DIV_ROUND_UP(max_vht_nss, 2);
+		if (supp_width == 0 &&
+		    ext_nss_bw == 3)
+			return DIV_ROUND_UP(3 * max_vht_nss, 4);
+		if (supp_width == 1 &&
+		    ext_nss_bw == 1)
+			return DIV_ROUND_UP(max_vht_nss, 2);
+		if (supp_width == 1 &&
+		    ext_nss_bw == 2)
+			return DIV_ROUND_UP(3 * max_vht_nss, 4);
+		break;
+	}
+
+	/* not covered or invalid combination received */
+	return max_vht_nss;
+}
 
 /* Authentication algorithms */
 #define WLAN_AUTH_OPEN 0
-- 
2.9.3