iwlwifi: mvm: enable RX chain diversity if needed

In some situations (see comment) it makes sense to enable both
chains (if available) to get better throughput by having chain
diversity available.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

diff --git a/drivers/net/wireless/iwlwifi/mvm/phy-ctxt.c b/drivers/net/wireless/iwlwifi/mvm/phy-ctxt.c
index 4902f3b..acb79af 100644 (file)
--- a/drivers/net/wireless/iwlwifi/mvm/phy-ctxt.c
+++ b/drivers/net/wireless/iwlwifi/mvm/phy-ctxt.c
@@ -156,6 +156,19 @@ static void iwl_mvm_phy_ctxt_cmd_data(struct iwl_mvm *mvm,
        idle_cnt = chains_static;
        active_cnt = chains_dynamic;
 
+       /* In scenarios where we only ever use a single-stream rates,
+        * i.e. legacy 11b/g/a associations, single-stream APs or even
+        * static SMPS, enable both chains to get diversity, improving
+        * the case where we're far enough from the AP that attenuation
+        * between the two antennas is sufficiently different to impact
+        * performance.
+        */
+       if (active_cnt == 1 && num_of_ant(mvm->fw->valid_rx_ant) > 1 &&
+           !mvm->cfg->rx_with_siso_diversity) {
+               idle_cnt = 2;
+               active_cnt = 2;
+       }
+
        cmd->rxchain_info = cpu_to_le32(mvm->fw->valid_rx_ant <<
                                        PHY_RX_CHAIN_VALID_POS);
        cmd->rxchain_info |= cpu_to_le32(idle_cnt << PHY_RX_CHAIN_CNT_POS);