Re: [PATCH] net: axienet: Clear stale AXI DMA TX/RX status before re-enabling interrupts

[Pandey, Radhey Shyam]

On 7/15/2026 6:20 PM, Kusuma Vasana wrote:

designate your patch to a tree - [PATCH net] or [PATCH net-next]
https://docs.kernel.org/process/maintainer-netdev.html

also keep all list in cc from get_maintainer.pl.

> The AXI DMA interrupt line is level-sensitive: it asserts whenever
> the IOC (XAXIDMA_IRQ_IOC_MASK) or DELAY (XAXIDMA_IRQ_DELAY_MASK) bits
> in the status register (XAXIDMA_TX_SR_OFFSET / XAXIDMA_RX_SR_OFFSET)
> are set and their corresponding enable bits in the control register
> are active.
>
> During TX/RX, interrupts are disabled in the control register while
> NAPI runs. Completions arriving in this window cause hardware to latch
> IOC/DELAY into the status register regardless of the control register
> mask state. After NAPI completion, re-enabling interrupts immediately
> re-asserts the IRQ line due to these stale status register bits, even
> when no new work is pending.
>
> This results in a stale interrupt and redundant NAPI poll cycle with
> no new work pending, causing unnecessary CPU processing.
>
> In the initial driver, the status register was cleared after polling
> all packets, which naturally consumed any status accumulated during
> processing. When the driver was converted to NAPI, status register
> clearing was moved to the ISR before polling begins, leaving no
> mechanism to clear status bits that arrive during the NAPI poll window.
> Fix the same.

rephrase - fix the same.

Once addressed- feel free to add:

Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxx>
Thanks!

> Signed-off-by: Kusuma Vasana <kusuma.vasana@xxxxxxx>
> ---
>   drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index fcf517069d16..29050c8d04e2 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -1018,6 +1018,13 @@ static int axienet_tx_poll(struct napi_struct *napi, int budget)
>   			netif_wake_queue(ndev);
>   	}
>   
> +	/* Clear stale IOC/DELAY bits that may have latched during the
> +	 * poll window to prevent a stale interrupt when there is no
> +	 * work pending.
> +	 */
> +	axienet_dma_out32(lp, XAXIDMA_TX_SR_OFFSET,
> +			  XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_DELAY_MASK);
> +
>   	if (packets < budget && napi_complete_done(napi, packets)) {
>   		/* Re-enable TX completion interrupts. This should
>   		 * cause an immediate interrupt if any TX packets are
> @@ -1293,6 +1300,13 @@ static int axienet_rx_poll(struct napi_struct *napi, int budget)
>   		cur_p = &lp->rx_bd_v[lp->rx_bd_ci];
>   	}
>   
> +	/* Clear stale IOC/DELAY bits that may have latched during the
> +	 * poll window to prevent a stale interrupt when there is no
> +	 * work pending.
> +	 */
> +	axienet_dma_out32(lp, XAXIDMA_RX_SR_OFFSET,
> +			  XAXIDMA_IRQ_IOC_MASK | XAXIDMA_IRQ_DELAY_MASK);
> +
>   	u64_stats_update_begin(&lp->rx_stat_sync);
>   	u64_stats_add(&lp->rx_packets, packets);
>   	u64_stats_add(&lp->rx_bytes, size);