RE: [PATCH v2] wifi: rtw88: increase TX report timeout to fix race condition

[Ping-Ke Shih]

luka.gejak@xxxxxxxxx <luka.gejak@xxxxxxxxx> wrote:
> From: Luka Gejak <luka.gejak@xxxxxxxxx>
> 
> The driver expects the firmware to report TX status within 500ms.
> However, a timeout can be triggered when the hardware performs
> background scans while under TX load. During these scans, the firmware
> stays off-channel for periods exceeding 500ms, delaying the delivery of
> TX reports back to the driver.
> 
> When this occurs, the purge timer fires prematurely and drops the
> tracking skbs from the queue. This results in the host stack
> interpreting the missing status as packet loss, leading to TCP window
> collapse. In testing with iperf3, this causes throughput to drop from
> ~90 Mbps to near-zero for approximately 2 seconds until the connection
> recovers.
> 
> Increase RTW_TX_PROBE_TIMEOUT to 2500ms for RTL8723DU. This duration is
> sufficient to accommodate off-channel dwell time during full background
> scans, ensuring the purge timer only trips during genuine firmware
> lockups and preventing unnecessary TCP retransmission cycles.
> 
> Fixes: e3037485c68e ("rtw88: new Realtek 802.11ac driver")

I don't think this commit introduce USB support. 

> Cc: stable@xxxxxxxxxxxxxxx
> Tested-by: Luka Gejak <luka.gejak@xxxxxxxxx>
> Signed-off-by: Luka Gejak <luka.gejak@xxxxxxxxx>
> ---
> Changes in v2:
>  -Isolated the change to RTL8723DU as requested by Ping-Ke
> 
>  drivers/net/wireless/realtek/rtw88/tx.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtw88/tx.c b/drivers/net/wireless/realtek/rtw88/tx.c
> index 3106edb84fb4..7fab83c3f6b5 100644
> --- a/drivers/net/wireless/realtek/rtw88/tx.c
> +++ b/drivers/net/wireless/realtek/rtw88/tx.c
> @@ -196,6 +196,7 @@ void rtw_tx_report_purge_timer(struct timer_list *t)
>  void rtw_tx_report_enqueue(struct rtw_dev *rtwdev, struct sk_buff *skb, u8 sn)
>  {
>         struct rtw_tx_report *tx_report = &rtwdev->tx_report;
> +       unsigned long timeout;

Declare RTW_TX_PROBE_TIMEOUT as default value.

unsigned long timeout = RTW_TX_PROBE_TIMEOUT;

>         unsigned long flags;
>         u8 *drv_data;
> 
> @@ -207,7 +208,13 @@ void rtw_tx_report_enqueue(struct rtw_dev *rtwdev, struct sk_buff *skb, u8 sn)
>         __skb_queue_tail(&tx_report->queue, skb);
>         spin_unlock_irqrestore(&tx_report->q_lock, flags);
> 
> -       mod_timer(&tx_report->purge_timer, jiffies + RTW_TX_PROBE_TIMEOUT);
> +       if (rtwdev->chip->id == RTW_CHIP_TYPE_8723D &&
> +           rtwdev->hci.type == RTW_HCI_TYPE_USB)
> +               timeout = msecs_to_jiffies(2500);

Only RTL8723DU uses different setting treated as an exception by if-condition.

> +       else
> +               timeout = RTW_TX_PROBE_TIMEOUT;
> +
> +       mod_timer(&tx_report->purge_timer, jiffies + timeout);
>  }
>  EXPORT_SYMBOL(rtw_tx_report_enqueue);
> 
> --
> 2.54.0