can: m_can: Batch acknowledge transmit events

Transmit events from the txe fifo can be batch acknowledged by
acknowledging the last read txe fifo item. This will save txe_count
writes which is important for peripheral chips.
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Link: https://lore.kernel.org/all/20221206115728.1056014-7-msp@baylibre.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -1023,7 +1023,9 @@ static int m_can_echo_tx_event(struct net_device *dev)
 	u32 txe_count = 0;
 	u32 m_can_txefs;
 	u32 fgi = 0;
+	int ack_fgi = -1;
 	int i = 0;
+	int err = 0;
 	unsigned int msg_mark;
 
 	struct m_can_classdev *cdev = netdev_priv(dev);
@@ -1038,28 +1040,29 @@ static int m_can_echo_tx_event(struct net_device *dev)
 	/* Get and process all sent elements */
 	for (i = 0; i < txe_count; i++) {
 		u32 txe, timestamp = 0;
-		int err;
 
 		/* get message marker, timestamp */
 		err = m_can_txe_fifo_read(cdev, fgi, 4, &txe);
 		if (err) {
 			netdev_err(dev, "TXE FIFO read returned %d\n", err);
-			return err;
+			break;
 		}
 
 		msg_mark = FIELD_GET(TX_EVENT_MM_MASK, txe);
 		timestamp = FIELD_GET(TX_EVENT_TXTS_MASK, txe) << 16;
 
-		/* ack txe element */
-		m_can_write(cdev, M_CAN_TXEFA, FIELD_PREP(TXEFA_EFAI_MASK,
-							  fgi));
+		ack_fgi = fgi;
 		fgi = (++fgi >= cdev->mcfg[MRAM_TXE].num ? 0 : fgi);
 
 		/* update stats */
 		m_can_tx_update_stats(cdev, msg_mark, timestamp);
 	}
 
-	return 0;
+	if (ack_fgi != -1)
+		m_can_write(cdev, M_CAN_TXEFA, FIELD_PREP(TXEFA_EFAI_MASK,
+							  ack_fgi));
+
+	return err;
 }
 
 static irqreturn_t m_can_isr(int irq, void *dev_id)