Re: [PATCH net-next] net: axienet: add a TX timeout handler to recover a lost DMA interrupt

[Andrew Lunn <andrew@lunn.ch>]

On Tue, Sep 15, 2026 at 09:55:34AM +0300, Sagi Maimon wrote:
> axienet_dma_err_handler() is the driver's only reset path, and the only
> two places that schedule it are axienet_tx_irq() and axienet_rx_irq(),
> both on the XAXIDMA_IRQ_ERROR_MASK branch.  Every route into recovery
> therefore depends on a DMA interrupt being delivered.
> 
> If a completion interrupt is lost the queue stops making progress with
> descriptors unreclaimed, and nothing ever schedules the reset: the error
> branch cannot run because no interrupt arrives, and NAPI is not polled
> because it is only scheduled from those same handlers.  The interface
> stays wedged until the driver is unloaded.
> 
> Add an .ndo_tx_timeout handler so the netdev watchdog provides a route
> into the existing reset path that does not depend on the interrupt that
> was lost.  The handler only queues the work; axienet_dma_err_handler()
> then performs the reset in process context, as it already does for the
> error-interrupt case.
> 
> .ndo_tx_timeout is added to axienet_netdev_ops alone.  On the dmaengine
> path lp->dma_err_task is never initialised - INIT_WORK() for it lives in
> axienet_init_legacy_dma() - so scheduling it there would be a bug, and
> watchdog_timeo is set in the same branch for that reason.
> 
> Tested on a Xilinx AXI Ethernet MAC by clearing PCI_MSIX_FLAGS_ENABLE
> underneath a running interface to drop completion interrupts: without
> this patch the TX queue stalls permanently, with it the watchdog fires
> and the interface resumes passing traffic.

Have you seen the hardware wedge without faking it by clearing
PCI_MSIX_FLAGS_ENABLE?

	Andrew