Re: [PATCH net-next v1 5/5] net: lan743x: add byte queue limits support

[Nicolai Buchwitz]

On 15.10.2026 17:00, Chris Babroski wrote:
> Report the bytes queued to and completed by each TX ring to BQL.
>
> Besides limiting how much data sits in the TX ring, this lets the stack
> stop a queue once the bytes in flight exceed the BQL limit. Without it,
> a queue is only stopped when its 128 entry ring is full, and the TX
> watchdog only looks at stopped queues. With light traffic it can take
> tens of seconds after a TX hang to fill the ring, before the watchdog
> timeout even starts counting.
>
> lan743x_tx_close() frees pending descriptors without completing them,
> so reset the BQL state there.
>
> Assisted-by: LLM
> Signed-off-by: Chris Babroski <cbabroski@xxxxxxxxxx>
> ---
>  drivers/net/ethernet/microchip/lan743x_main.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/drivers/net/ethernet/microchip/lan743x_main.c 
> b/drivers/net/ethernet/microchip/lan743x_main.c
> index 2545a846478d..7739fa49fc44 100644
> --- a/drivers/net/ethernet/microchip/lan743x_main.c
> +++ b/drivers/net/ethernet/microchip/lan743x_main.c
> @@ -1708,10 +1708,23 @@ static int lan743x_tx_next_index(struct 
> lan743x_tx *tx, int index)
>
>  static void lan743x_tx_release_completed_descriptors(struct lan743x_tx 
> *tx)
>  {
> +	struct lan743x_tx_buffer_info *buffer_info;
> +	unsigned int bytes = 0;
> +	unsigned int pkts = 0;
> +
>  	while (le32_to_cpu(*tx->head_cpu_ptr) != (tx->last_head)) {
> +		buffer_info = &tx->buffer_info[tx->last_head];
> +		if (buffer_info->skb) {
> +			bytes += buffer_info->skb->len;
> +			pkts++;
> +		}
>  		lan743x_tx_release_desc(tx, tx->last_head, false);
>  		tx->last_head = lan743x_tx_next_index(tx, tx->last_head);
>  	}
> +
> +	netdev_tx_completed_queue(netdev_get_tx_queue(tx->adapter->netdev,
> +						      tx->channel_number),
> +				  pkts, bytes);
>  }
>
>  static void lan743x_tx_release_all_descriptors(struct lan743x_tx *tx)
> @@ -2003,6 +2016,10 @@ static void lan743x_tx_frame_end(struct 
> lan743x_tx *tx,
>  	if (ignore_sync)
>  		buffer_info->flags |= TX_BUFFER_INFO_FLAG_IGNORE_SYNC;
>
> +	netdev_tx_sent_queue(netdev_get_tx_queue(adapter->netdev,
> +						 tx->channel_number),
> +			     skb->len);
> +
>  	tx_descriptor = &tx->ring_cpu_ptr[tx->frame_tail];
>  	tx_descriptor->data0 = cpu_to_le32(tx->frame_data0);
>  	tx->frame_tail = lan743x_tx_next_index(tx, tx->frame_tail);
> @@ -2276,6 +2293,8 @@ static void lan743x_tx_close(struct lan743x_tx 
> *tx)
>  				 0, 1000, 20000, 100);
>
>  	lan743x_tx_release_all_descriptors(tx);
> +	netdev_tx_reset_queue(netdev_get_tx_queue(adapter->netdev,
> +						  tx->channel_number));
>
>  	tx->rqd_descriptors = 0;

Reviewed-by: Nicolai Buchwitz <nb@xxxxxxxxxxx>

Thanks,
Nicolai