[PATCH v5 1/3] can: rockchip_canfd: prevent TX stall on echo skb failure

rkcanfd_start_xmit() advances tx_head and requests transmission even when
can_put_echo_skb() fails. This creates a pending TX entry without the echo
skb that the RXSTX completion path needs to match the self-received frame.
The entry cannot be completed, and the netdev TX queue can remain stopped
after the two-entry software FIFO fills.

Install the echo skb before loading the hardware TX buffer. If installation
fails, account the frame as dropped and leave both the hardware FIFO and
software TX state unchanged. After the echo skb is installed, use the
stored echo skb as the source for the hardware frame data.

This depends on the standalone can_put_echo_skb() ownership fix. It makes
the remaining -EINVAL path consume the skb and was posted at:

Link: https://lore.kernel.org/linux-can/[email protected]
Fixes: b6661d73290c ("can: rockchip_canfd: add TX PATH")
Cc: [email protected]
Signed-off-by: Cunhao Lu <[email protected]>
---
 drivers/net/can/rockchip/rockchip_canfd-tx.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/net/can/rockchip/rockchip_canfd-tx.c b/drivers/net/can/rockchip/rockchip_canfd-tx.c
index 12200dcfd338..86fa8f2e1c8b 100644
--- a/drivers/net/can/rockchip/rockchip_canfd-tx.c
+++ b/drivers/net/can/rockchip/rockchip_canfd-tx.c
@@ -88,7 +88,16 @@ netdev_tx_t rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		return NETDEV_TX_BUSY;
 	}
 
-	cfd = (struct canfd_frame *)skb->data;
+	tx_head = rkcanfd_get_tx_head(priv);
+	frame_len = can_skb_get_frame_len(skb);
+	err = can_put_echo_skb(skb, ndev, tx_head, frame_len);
+	if (err) {
+		ndev->stats.tx_dropped++;
+		return NETDEV_TX_OK;
+	}
+
+	skb = priv->can.echo_skb[tx_head];
+	cfd = (const struct canfd_frame *)skb->data;
 
 	if (cfd->can_id & CAN_EFF_FLAG) {
 		reg_frameinfo = RKCANFD_REG_FD_FRAMEINFO_FRAME_FORMAT;
@@ -114,7 +123,6 @@ netdev_tx_t rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 					    cfd->len);
 	}
 
-	tx_head = rkcanfd_get_tx_head(priv);
 	reg_cmd = RKCANFD_REG_CMD_TX_REQ(tx_head);
 
 	rkcanfd_write(priv, RKCANFD_REG_FD_TXFRAMEINFO, reg_frameinfo);
@@ -123,10 +131,7 @@ netdev_tx_t rkcanfd_start_xmit(struct sk_buff *skb, struct net_device *ndev)
 		rkcanfd_write(priv, RKCANFD_REG_FD_TXDATA0 + i,
 			      *(u32 *)(cfd->data + i));
 
-	frame_len = can_skb_get_frame_len(skb);
-	err = can_put_echo_skb(skb, ndev, tx_head, frame_len);
-	if (!err)
-		netdev_sent_queue(priv->ndev, frame_len);
+	netdev_sent_queue(priv->ndev, frame_len);
 
 	WRITE_ONCE(priv->tx_head, priv->tx_head + 1);
 

-- 
2.34.1