ath5k: optimize tx status processing

Use ACCESS_ONCE to reduce the number of variable reloads on uncached memory
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath5k/desc.c

@@ -401,32 +401,38 @@ static int ath5k_hw_proc_4word_tx_status(struct ath5k_hw *ah,
 {
 	struct ath5k_hw_4w_tx_ctl *tx_ctl;
 	struct ath5k_hw_tx_status *tx_status;
+	u32 txstat0, txstat1, txctl2;
 
 	tx_ctl = &desc->ud.ds_tx5212.tx_ctl;
 	tx_status = &desc->ud.ds_tx5212.tx_stat;
 
+	txstat1 = ACCESS_ONCE(tx_status->tx_status_1);
+
 	/* No frame has been send or error */
-	if (unlikely(!(tx_status->tx_status_1 & AR5K_DESC_TX_STATUS1_DONE)))
+	if (unlikely(!(txstat1 & AR5K_DESC_TX_STATUS1_DONE)))
 		return -EINPROGRESS;
 
+	txstat0 = ACCESS_ONCE(tx_status->tx_status_0);
+	txctl2 = ACCESS_ONCE(tx_ctl->tx_control_2);
+
 	/*
 	 * Get descriptor status
 	 */
-	ts->ts_tstamp = AR5K_REG_MS(tx_status->tx_status_0,
+	ts->ts_tstamp = AR5K_REG_MS(txstat0,
 		AR5K_DESC_TX_STATUS0_SEND_TIMESTAMP);
-	ts->ts_shortretry = AR5K_REG_MS(tx_status->tx_status_0,
+	ts->ts_shortretry = AR5K_REG_MS(txstat0,
 		AR5K_DESC_TX_STATUS0_SHORT_RETRY_COUNT);
-	ts->ts_longretry = AR5K_REG_MS(tx_status->tx_status_0,
+	ts->ts_longretry = AR5K_REG_MS(txstat0,
 		AR5K_DESC_TX_STATUS0_LONG_RETRY_COUNT);
-	ts->ts_seqnum = AR5K_REG_MS(tx_status->tx_status_1,
+	ts->ts_seqnum = AR5K_REG_MS(txstat1,
 		AR5K_DESC_TX_STATUS1_SEQ_NUM);
-	ts->ts_rssi = AR5K_REG_MS(tx_status->tx_status_1,
+	ts->ts_rssi = AR5K_REG_MS(txstat1,
 		AR5K_DESC_TX_STATUS1_ACK_SIG_STRENGTH);
-	ts->ts_antenna = (tx_status->tx_status_1 &
+	ts->ts_antenna = (txstat1 &
 		AR5K_DESC_TX_STATUS1_XMIT_ANTENNA_5212) ? 2 : 1;
 	ts->ts_status = 0;
 
-	ts->ts_final_idx = AR5K_REG_MS(tx_status->tx_status_1,
+	ts->ts_final_idx = AR5K_REG_MS(txstat1,
 			AR5K_DESC_TX_STATUS1_FINAL_TS_IX_5212);
 
 	/* The longretry counter has the number of un-acked retries
@@ -437,17 +443,17 @@ static int ath5k_hw_proc_4word_tx_status(struct ath5k_hw *ah,
 	ts->ts_retry[ts->ts_final_idx] = ts->ts_longretry;
 	switch (ts->ts_final_idx) {
 	case 3:
-		ts->ts_retry[2] = AR5K_REG_MS(tx_ctl->tx_control_2,
+		ts->ts_retry[2] = AR5K_REG_MS(txctl2,
 			AR5K_4W_TX_DESC_CTL2_XMIT_TRIES2);
 		ts->ts_longretry += ts->ts_retry[2];
 		/* fall through */
 	case 2:
-		ts->ts_retry[1] = AR5K_REG_MS(tx_ctl->tx_control_2,
+		ts->ts_retry[1] = AR5K_REG_MS(txctl2,
 			AR5K_4W_TX_DESC_CTL2_XMIT_TRIES1);
 		ts->ts_longretry += ts->ts_retry[1];
 		/* fall through */
 	case 1:
-		ts->ts_retry[0] = AR5K_REG_MS(tx_ctl->tx_control_2,
+		ts->ts_retry[0] = AR5K_REG_MS(txctl2,
 			AR5K_4W_TX_DESC_CTL2_XMIT_TRIES1);
 		ts->ts_longretry += ts->ts_retry[0];
 		/* fall through */
@@ -456,15 +462,14 @@ static int ath5k_hw_proc_4word_tx_status(struct ath5k_hw *ah,
 	}
 
 	/* TX error */
-	if (!(tx_status->tx_status_0 & AR5K_DESC_TX_STATUS0_FRAME_XMIT_OK)) {
-		if (tx_status->tx_status_0 &
-				AR5K_DESC_TX_STATUS0_EXCESSIVE_RETRIES)
+	if (!(txstat0 & AR5K_DESC_TX_STATUS0_FRAME_XMIT_OK)) {
+		if (txstat0 & AR5K_DESC_TX_STATUS0_EXCESSIVE_RETRIES)
 			ts->ts_status |= AR5K_TXERR_XRETRY;
 
-		if (tx_status->tx_status_0 & AR5K_DESC_TX_STATUS0_FIFO_UNDERRUN)
+		if (txstat0 & AR5K_DESC_TX_STATUS0_FIFO_UNDERRUN)
 			ts->ts_status |= AR5K_TXERR_FIFO;
 
-		if (tx_status->tx_status_0 & AR5K_DESC_TX_STATUS0_FILTERED)
+		if (txstat0 & AR5K_DESC_TX_STATUS0_FILTERED)
 			ts->ts_status |= AR5K_TXERR_FILT;
 	}