[PATCH net 3/4] net: ethernet: cortina: Carry over frag counter

[Linus Walleij <linusw@kernel.org>]

The gmac_rx() NAPI poll function assembles packets in an
SKB from a ring buffer.

If the ring buffer gets completely emptied during a poll cycle,
we exit gmac_rx(), but the packet is not yet completely
assembled in the SKB, yet the fragment counter frag_nr is
reset to zero on the next invocation.

Solve this by making the RX fragment counter a part of the
port struct, and carry it over between invocations.

Reset the fragment counter only right after calling
napi_gro_frags(), on error (after calling napi_free_frags())
or if stopping the port.

Reset it in some place where not strictly necessary just to
emphasize what is going on.

This was found by Sashiko during normal patch review.

Fixes: 4d5ae32f5e1e ("net: ethernet: Add a driver for Gemini gigabit ethernet")
Link: https://sashiko.dev/#/patchset/20260505-gemini-ethernet-fix-v2-1-997c31d06079%40kernel.org
Signed-off-by: Linus Walleij <linusw@kernel.org>
---
 drivers/net/ethernet/cortina/gemini.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cortina/gemini.c b/drivers/net/ethernet/cortina/gemini.c
index d5a56366fb43..4c762229ce42 100644
--- a/drivers/net/ethernet/cortina/gemini.c
+++ b/drivers/net/ethernet/cortina/gemini.c
@@ -123,6 +123,7 @@ struct gemini_ethernet_port {
 	struct hrtimer		rx_coalesce_timer;
 	unsigned int		rx_coalesce_nsecs;
 	struct sk_buff		*rx_skb;
+	unsigned int		rx_frag_nr;
 
 	unsigned int		freeq_refill;
 	struct gmac_txq		txq[TX_QUEUE_NUM];
@@ -1444,6 +1445,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 	unsigned short m = (1 << port->rxq_order) - 1;
 	struct gemini_ethernet *geth = port->geth;
 	void __iomem *ptr_reg = port->rxq_rwptr;
+	unsigned int frag_nr = port->rx_frag_nr;
 	struct sk_buff *skb = port->rx_skb;
 	unsigned int frame_len, frag_len;
 	struct gmac_rxdesc *rx = NULL;
@@ -1457,7 +1459,6 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 	unsigned short r, w;
 	union dma_rwptr rw;
 	dma_addr_t mapping;
-	int frag_nr = 0;
 
 	spin_lock_irqsave(&geth->irq_lock, flags);
 	rw.bits32 = readl(ptr_reg);
@@ -1497,6 +1498,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 			if (skb) {
 				napi_free_frags(&port->napi);
 				skb = NULL;
+				frag_nr = 0;
 			}
 			continue;
 		}
@@ -1507,6 +1509,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 				napi_free_frags(&port->napi);
 				port->stats.rx_dropped++;
 				skb = NULL;
+				frag_nr = 0;
 			}
 
 			skb = gmac_skb_if_good_frame(port, word0, frame_len);
@@ -1541,6 +1544,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 		if (word3.bits32 & EOF_BIT) {
 			napi_gro_frags(&port->napi);
 			skb = NULL;
+			frag_nr = 0;
 			--budget;
 		}
 		continue;
@@ -1549,6 +1553,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 		if (skb) {
 			napi_free_frags(&port->napi);
 			skb = NULL;
+			frag_nr = 0;
 		}
 
 		if (mapping)
@@ -1558,6 +1563,7 @@ static unsigned int gmac_rx(struct net_device *netdev, unsigned int budget)
 	}
 
 	port->rx_skb = skb;
+	port->rx_frag_nr = frag_nr;
 	writew(r, ptr_reg);
 	return budget;
 }
@@ -1886,6 +1892,7 @@ static int gmac_stop(struct net_device *netdev)
 	gmac_stop_dma(port);
 	napi_disable(&port->napi);
 	port->rx_skb = NULL;
+	port->rx_frag_nr = 0;
 
 	gmac_enable_irq(netdev, 0);
 	gmac_cleanup_rxq(netdev);

-- 
2.54.0