[PATCH net v2 1/4] net: axienet: start the TX queue in axienet_open()

[Sagi Maimon <maimon.sagi@gmail.com>]

axienet_open() never starts the transmit queue, and nothing else does
either: __dev_open() and dev_activate() leave the driver's queue state
alone.

axienet_start_xmit() stops the queue with netif_stop_queue() when the TX
ring fills, and axienet_tx_poll() wakes it again as completions free
descriptors.  If the interface is brought down while the queue is
stopped, __QUEUE_STATE_DRV_XOFF survives into the next axienet_open().
The ring is reinitialised empty, so no TX completion ever arrives to run
the wake in axienet_tx_poll(), and the interface cannot transmit until
the driver is reloaded.  The resume path is unaffected only because
netif_device_attach() wakes the queues.

Start the queue at the end of a successful axienet_open(), as most
drivers do.

Tested on an AXI Ethernet MAC behind a PCIe endpoint: traffic passes,
and resumes after each of ten down/up cycles and five module reloads,
all made with traffic running.  A queue left stopped across a down/up
cycle, with the ring full, was not reproduced.

Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
Assisted-by: LLM sparse
Signed-off-by: Sagi Maimon <maimon.sagi@gmail.com>
---
 drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
index 782f903d318f..fb26d2e39fac 100644
--- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
+++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
@@ -1700,6 +1700,11 @@ static int axienet_open(struct net_device *ndev)
 			goto err_phy;
 	}
 
+	/* Nothing else clears a stop left over from before the last close:
+	 * the ring is empty, so no TX completion will wake the queue.
+	 */
+	netif_start_queue(ndev);
+
 	return 0;
 
 err_free_eth_irq:
-- 
2.47.0