Re: [PATCH net v3] net: airoha: fix BQL underflow in shared QDMA TX ring

[Simon Horman <horms@kernel.org>]

On Sat, Jun 20, 2026 at 05:04:51PM +0200, Lorenzo Bianconi wrote:
> When multiple netdevs share a QDMA TX ring and one device is stopped,
> netdev_tx_reset_subqueue() zeroes that device's BQL counters while its
> pending skbs remain in the shared HW TX ring. When NAPI later completes
> those skbs via netdev_tx_completed_queue(), the already-zeroed
> dql->num_queued counter underflows.
> 
> Fix the issue:
> - Remove netdev_tx_reset_subqueue() from airoha_dev_stop() so pending
>   skbs are completed naturally by NAPI with proper BQL accounting.
> - Rework airoha_qdma_tx_cleanup() to disable TX DMA, flush BQL
>   counters, DMA-unmap and free all pending skbs while skb->dev
>   references are still valid. Use a per-queue flushing flag checked
>   under q->lock in airoha_dev_xmit() to prevent races between teardown
>   and transmit. Call airoha_qdma_stop_napi() before
>   airoha_qdma_tx_cleanup() at the call sites.
> - Move DMA engine start into probe. Split DMA teardown so TX DMA is
>   disabled in airoha_qdma_tx_cleanup() and RX DMA in
>   airoha_qdma_cleanup().
> - Remove qdma->users counter since DMA lifetime is now tied to
>   probe/cleanup rather than per-netdev open/stop.
> 
> Fixes: a9c2ca61fec7 ("net: airoha: Support multiple net_devices for a single FE GDM port")
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
> Changes in v3:
> - Remove airoha_qdma users counter.
> - Drop DEV_STATE_FLUSH bit and add per-queue flushing bool to avoid any
>   race between airoha_qdma_tx_flush() and airoha_dev_xmit().
> - Refactor airoha_qdma_cleanup_tx_queue().
> - Rename airoha_qdma_cleanup_tx_queue() in airoha_qdma_tx_cleanup().
> - Link to v2: https://lore.kernel.org/r/20260619-airoha-bql-fixes-v2-1-4351d6a24484@kernel.org
> 

Thanks for the updates.

Reviewed-by: Simon Horman <horms@kernel.org>