Instead of acknowledging every item of the fifo, only acknowledge the
last item read. This behavior is documented in the datasheet. The new
getindex will be the acknowledged item + 1.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
---
 drivers/net/can/m_can/m_can.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/can/m_can/m_can.c b/drivers/net/can/m_can/m_can.c
index 5572a6b3b94c..56f07f2023dd 100644
--- a/drivers/net/can/m_can/m_can.c
+++ b/drivers/net/can/m_can/m_can.c
@@ -529,9 +529,6 @@ static int m_can_read_fifo(struct net_device *dev, u32 fgi)
 	}
 	stats->rx_packets++;
 
-	/* acknowledge rx fifo 0 */
-	m_can_write(cdev, M_CAN_RXF0A, fgi);
-
 	timestamp = FIELD_GET(RX_BUF_RXTS_MASK, fifo_header.dlc) << 16;
 
 	m_can_receive_skb(cdev, skb, timestamp);
@@ -552,8 +549,9 @@ static int m_can_do_rx_poll(struct net_device *dev, int quota)
 	u32 rxfs;
 	u32 rx_count;
 	u32 fgi;
+	int ack_fgi = -1;
 	int i;
-	int err;
+	int err = 0;
 
 	rxfs = m_can_read(cdev, M_CAN_RXF0S);
 	if (!(rxfs & RXFS_FFL_MASK)) {
@@ -567,13 +565,20 @@ static int m_can_do_rx_poll(struct net_device *dev, int quota)
 	for (i = 0; i < rx_count && quota > 0; ++i) {
 		err = m_can_read_fifo(dev, fgi);
 		if (err)
-			return err;
+			break;
 
 		quota--;
 		pkts++;
+		ack_fgi = fgi;
 		fgi = (++fgi >= cdev->mcfg[MRAM_RXF0].num ? 0 : fgi);
 	}
 
+	if (ack_fgi != -1)
+		m_can_write(cdev, M_CAN_RXF0A, ack_fgi);
+
+	if (err)
+		return err;
+
 	return pkts;
 }
 
-- 
2.38.1