netdev - Re: [PATCH] net: ks8851: Fix potential TX stall after interface reopen

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Message-ID: <8e4c281e-06d8-47bf-9347-d82107f00165@intel.com>
Date: Wed, 10 Jul 2024 16:48:42 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Ronald Wahl <rwahl@....de>
CC: Ronald Wahl <ronald.wahl@...itan.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
	<horms@...nel.org>, <netdev@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH] net: ks8851: Fix potential TX stall after interface
 reopen



On 7/9/2024 12:58 PM, Ronald Wahl wrote:
> From: Ronald Wahl <ronald.wahl@...itan.com>
> 
> The amount of TX space in the hardware buffer is tracked in the tx_space
> variable. The initial value is currently only set during driver probing.
> 
> After closing the interface and reopening it the tx_space variable has
> the last value it had before close. If it is smaller than the size of
> the first send packet after reopeing the interface the queue will be
> stopped. The queue is woken up after receiving a TX interrupt but this
> will never happen since we did not send anything.
> 
> This commit moves the initialization of the tx_space variable to the
> ks8851_net_open function right before starting the TX queue. Also query
> the value from the hardware instead of using a hard coded value.
> 
> Only the SPI chip variant is affected by this issue because only this
> driver variant actually depends on the tx_space variable in the xmit
> function.

I'm curious if this dependency could be removed?

Otherwise:
Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>

> 
> Fixes: 3dc5d4454545 ("net: ks8851: Fix TX stall caused by TX buffer overrun")
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Simon Horman <horms@...nel.org>
> Cc: netdev@...r.kernel.org
> Cc: stable@...r.kernel.org # 5.10+
> Signed-off-by: Ronald Wahl <ronald.wahl@...itan.com>
> ---
>  drivers/net/ethernet/micrel/ks8851_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/micrel/ks8851_common.c b/drivers/net/ethernet/micrel/ks8851_common.c
> index 6453c92f0fa7..03a554df6e7a 100644
> --- a/drivers/net/ethernet/micrel/ks8851_common.c
> +++ b/drivers/net/ethernet/micrel/ks8851_common.c
> @@ -482,6 +482,7 @@ static int ks8851_net_open(struct net_device *dev)
>  	ks8851_wrreg16(ks, KS_IER, ks->rc_ier);
> 
>  	ks->queued_len = 0;
> +	ks->tx_space = ks8851_rdreg16(ks, KS_TXMIR);
>  	netif_start_queue(ks->netdev);
> 
>  	netif_dbg(ks, ifup, ks->netdev, "network device up\n");
> @@ -1101,7 +1102,6 @@ int ks8851_probe_common(struct net_device *netdev, struct device *dev,
>  	int ret;
> 
>  	ks->netdev = netdev;
> -	ks->tx_space = 6144;
> 
>  	ks->gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
>  	ret = PTR_ERR_OR_ZERO(ks->gpio);
> --
> 2.45.2
> 
>