iwlwifi: Use RTS/CTS as the preferred protection mechanism for 6000 series

When 802.11g was introduced, we had RTS/CTS and CTS-to-Self protection
mechanisms. In an HT Beacon, HT stations use the "Operating Mode" field
in the HT Information Element to determine whether or not to use
protection.

The Operating Mode field has 4 possible settings: 0-3:
Mode 0: If all stations in the BSS are 20/40 MHz HT capable, or if the
BSS is 20/40 MHz capable, or if all stations in the BSS are 20 MHz HT
stations in a 20 MHz BSS
Mode 1: used if there are non-HT stations or APs using the primary or
secondary channels
Mode 2: if only HT stations are associated in the BSS and at least one
20 MHz HT station is associated.
Mode 3: used if one or more non-HT stations are associated in the BSS.

When in operating modes 1 or 3, and the Use_Protection field is 1 in the
Beacon's ERP IE, all HT transmissions must be protected using RTS/CTS or
CTS-to-Self.

By default, CTS-to-self is the preferred protection mechanism for less
overhead and higher throughput; but using the full RTS/CTS will better
protect the inner exchange from interference, especially in
highly-congested environment.

For 6000 series WIFI NIC, RTS/CTS protection mechanism is the
recommended choice for HT traffic based on the HW design.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-rs.c b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
index 18af37c964cb..469d56321d88 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-rs.c
@@ -418,6 +418,15 @@ static void rs_tl_turn_on_agg(struct iwl_priv *priv, u8 tid,
 	else if (tid == IWL_AGG_ALL_TID)
 		for (tid = 0; tid < TID_MAX_LOAD_COUNT; tid++)
 			rs_tl_turn_on_agg_for_tid(priv, lq_data, tid, sta);
+	if (priv->cfg->use_rts_for_ht) {
+		/*
+		 * switch to RTS/CTS if it is the prefer protection method
+		 * for HT traffic
+		 */
+		IWL_DEBUG_HT(priv, "use RTS/CTS protection for HT\n");
+		priv->staging_rxon.flags &= ~RXON_FLG_SELF_CTS_EN;
+		iwlcore_commit_rxon(priv);
+	}
 }
 
 static inline int get_num_of_ant_from_rate(u32 rate_n_flags)