Re: [PATCH net v3 1/2] net: ethernet: mtk_wed: skip ring reset in wdma_tx_ring_setup for WED v3

[Zhi-Jun You <hujy652@gmail.com>]

On Sat, Jul 25, 2026 at 01:20:39AM +0800, Zhi-Jun You wrote:
> Currently WED v3 tx wdma ring, ring reset happens in a separate code
> block unconditionally.
> 
> Moreover, v3 has double the size of wdma_desc and has different init
> values. mtk_wed_ring_reset doens't deal with that and would corrupt the
> wdma_desc.
> 
> Fix this by skipping mtk_wed_ring_reset in mtk_wdma_tx_ring_setup for
> WED v3.

Commenting on Sashiko's report:
https://sashiko.dev/#/patchset/20260724172040.1653-1-hujy652%40gmail.com

> 
> Fixes: e2f64db13aa1 ("net: ethernet: mtk_wed: introduce WED support for MT7988")
> Signed-off-by: Zhi-Jun You <hujy652@gmail.com>
> ---
> Changes in v3:
> - new patch addressing WED v3 ring reset issue raised by Sashiko
> - Link to the review: https://lore.kernel.org/netdev/20260630144831.1109-1-hujy652@gmail.com/
> ---
>  drivers/net/ethernet/mediatek/mtk_wed.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mediatek/mtk_wed.c b/drivers/net/ethernet/mediatek/mtk_wed.c
> index 10d9beaae372..7d2775a97fa0 100644
> --- a/drivers/net/ethernet/mediatek/mtk_wed.c
> +++ b/drivers/net/ethernet/mediatek/mtk_wed.c
> @@ -1938,7 +1938,7 @@ mtk_wed_wdma_tx_ring_setup(struct mtk_wed_device *dev, int idx, int size,
>  	wdma_w32(dev, MTK_WDMA_RING_TX(idx) + MTK_WED_RING_OFS_CPU_IDX, 0);
>  	wdma_w32(dev, MTK_WDMA_RING_TX(idx) + MTK_WED_RING_OFS_DMA_IDX, 0);
>  
> -	if (reset)
> +	if (!mtk_wed_is_v3_or_greater(dev->hw) && reset)
>  		mtk_wed_ring_reset(wdma, MTK_WED_WDMA_RING_SIZE, true);
>  
>  	if (!idx)  {

-This is a pre-existing issue, but while reviewing the WDMA ring reset logic,
 I noticed what looks like reversed logic in mtk_wdma_rx_reset():
 drivers/net/ethernet/mediatek/mtk_wed.c:mtk_wdma_rx_reset() {
 	...
 	for (i = 0; i < ARRAY_SIZE(dev->rx_wdma); i++) {
 		if (dev->rx_wdma[i].desc)
 			continue;
 		wdma_w32(dev,
 			 MTK_WDMA_RING_RX(i) + MTK_WED_RING_OFS_CPU_IDX, 0);
 	}
 	...
 }
 Does the if (dev->rx_wdma[i].desc) continue; check skip the CPU_IDX reset for
 active rings?
 When a WDMA RX reset occurs (e.g., during recovery from a hang), the hardware
 index is reset to 0, but the CPU_IDX register won't be reset for active rings
 since they have a non-NULL desc.
 Could this desynchronize the driver and hardware, leading to a permanent stall
 of the WDMA RX rings and network traffic failure?
 - ACK I will add a patch addressing this.

 Best regards,
 Zhi-Jun
> -- 
> 2.47.3
>