[PATCH v2 2/2] net, can, ifi: loopback Tx message in IFI block

[Heiko Schocher <hs@denx.de>]

Current ifi driver reads first Rx messages, than loopback
the Tx message, if the IFI_CANFD_INTERRUPT_TXFIFO_REMOVE
bit is set. This can lead into the case, that Rx messages
overhelm Tx messages!

Fixed this in the following way:

Set in the IFI_CANFD_TXFIFO_DLC register the FN value to
1, so the IFI block loopsback itself the Tx message when
sended correctly on the canfd bus. Only the IFI block can
insert the Tx message in the correct place.

The linux driver now needs only to free the skb, when
the Tx message was sended correctly.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Marek Vasut <marex@denx.de>
---

Changes in v2:
- add Reviewed-by from Marek, fixed comment into one liner

 drivers/net/can/ifi_canfd/ifi_canfd.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/can/ifi_canfd/ifi_canfd.c b/drivers/net/can/ifi_canfd/ifi_canfd.c
index 05feb8177936..ee74ee8f9b38 100644
--- a/drivers/net/can/ifi_canfd/ifi_canfd.c
+++ b/drivers/net/can/ifi_canfd/ifi_canfd.c
@@ -211,6 +211,7 @@ struct ifi_canfd_priv {
 	struct napi_struct	napi;
 	struct net_device	*ndev;
 	void __iomem		*base;
+	unsigned int		tx_len;
 };
 
 static void ifi_canfd_irq_enable(struct net_device *ndev, bool enable)
@@ -617,8 +618,10 @@ static irqreturn_t ifi_canfd_isr(int irq, void *dev_id)
 
 	/* TX IRQ */
 	if (isr & IFI_CANFD_INTERRUPT_TXFIFO_REMOVE) {
-		stats->tx_bytes += can_get_echo_skb(ndev, 0);
+		can_free_echo_skb(ndev, 0);
+		stats->tx_bytes += priv->tx_len;
 		stats->tx_packets++;
+		priv->tx_len = 0;
 		can_led_event(ndev, CAN_LED_EVENT_TX);
 	}
 
@@ -889,6 +892,7 @@ static netdev_tx_t ifi_canfd_start_xmit(struct sk_buff *skb,
 	}
 
 	txdlc = can_len2dlc(cf->len);
+	priv->tx_len = txdlc;
 	if ((priv->can.ctrlmode & CAN_CTRLMODE_FD) && can_is_canfd_skb(skb)) {
 		txdlc |= IFI_CANFD_TXFIFO_DLC_EDL;
 		if (cf->flags & CANFD_BRS)
@@ -898,6 +902,9 @@ static netdev_tx_t ifi_canfd_start_xmit(struct sk_buff *skb,
 	if (cf->can_id & CAN_RTR_FLAG)
 		txdlc |= IFI_CANFD_TXFIFO_DLC_RTR;
 
+	/* set FNR to 1, so we get our Tx Message looped back into RxFIFO */
+	txdlc += (1 << IFI_CANFD_TXFIFO_DLC_FNR_OFFSET);
+
 	/* message ram configuration */
 	writel(txid, priv->base + IFI_CANFD_TXFIFO_ID);
 	writel(txdlc, priv->base + IFI_CANFD_TXFIFO_DLC);
-- 
2.14.3