netdev - Re: [PATCH net] net: stmmac: fix completely hung TX when using TSO

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Date:   Tue, 6 Jun 2017 10:00:39 +0200
From:   Giuseppe CAVALLARO <peppe.cavallaro@...com>
To:     Niklas Cassel <niklas.cassel@...s.com>,
        Alexandre Torgue <alexandre.torgue@...com>
CC:     Niklas Cassel <niklass@...s.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: stmmac: fix completely hung TX when using TSO

Hi Niklas

I get the point and I acked the patch but Alex, please, can you confirm
that this issue has never seen on your boxes where the TSO has been
fully tested? The initial development (commit f748be531) introduces
the following:
     (last_segment) && (buff_size < TSO_MAX_BUFF_SIZE),
...

On 6/6/2017 9:25 AM, Niklas Cassel wrote:
> stmmac_tso_allocator can fail to set the Last Descriptor bit
> on a descriptor that actually was the last descriptor.
>
> This happens when the buffer of the last descriptor ends
> up having a size of exactly TSO_MAX_BUFF_SIZE.
>
> When the IP eventually reaches the next last descriptor,
> which actually has the bit set, the DMA will hang.
>
> When the DMA hangs, we get a tx timeout, however,
> since stmmac does not do a complete reset of the IP
> in stmmac_tx_timeout, we end up in a state with
> completely hung TX.
>
> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>

Acked-by: Giuseppe Cavallaro <peppe.cavallaro@...com>

> ---
>   drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 68a188e74c54..440bea049a7f 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2723,7 +2723,7 @@ static void stmmac_tso_allocator(struct stmmac_priv *priv, unsigned int des,
>   
>   		priv->hw->desc->prepare_tso_tx_desc(desc, 0, buff_size,
>   			0, 1,
> -			(last_segment) && (buff_size < TSO_MAX_BUFF_SIZE),
> +			(last_segment) && (tmp_len <= TSO_MAX_BUFF_SIZE),
>   			0, 0);
>   
>   		tmp_len -= TSO_MAX_BUFF_SIZE;

Regards
Peppe