iwlwifi: allow to restrict Tx aggregation size per-device

A few slave bus devices show better performance when we
reduce the size of the Tx A-MPDU.

Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>

drivers/net/wireless/iwlwifi/iwl-config.h

@@ -246,6 +246,7 @@ struct iwl_pwr_tx_backoff {
  * @nvm_hw_section_num: the ID of the HW NVM section
  * @pwr_tx_backoffs: translation table between power limits and backoffs
  * @max_rx_agg_size: max RX aggregation size of the ADDBA request/response
+ * @max_tx_agg_size: max TX aggregation size of the ADDBA request/response
  *
  * We enable the driver to be backward compatible wrt. hardware features.
  * API differences in uCode shouldn't be handled here but through TLVs
@@ -285,6 +286,7 @@ struct iwl_cfg {
 	const char *default_nvm_file;
 	unsigned int max_rx_agg_size;
 	bool disable_dummy_notification;
+	unsigned int max_tx_agg_size;
 };
 
 /*

drivers/net/wireless/iwlwifi/mvm/ops.c

@@ -403,6 +403,9 @@ iwl_op_mode_mvm_start(struct iwl_trans *trans, const struct iwl_cfg *cfg,
 	if (cfg->max_rx_agg_size)
 		hw->max_rx_aggregation_subframes = cfg->max_rx_agg_size;
 
+	if (cfg->max_tx_agg_size)
+		hw->max_tx_aggregation_subframes = cfg->max_tx_agg_size;
+
 	op_mode = hw->priv;
 	op_mode->ops = &iwl_mvm_ops;