linux-kernel - Re: [net PATCH] net: ravb: Fix max TX frame size for RZ/V2M

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Message-ID: <20250109124538.GR2766897@ragnatech.se>
Date: Thu, 9 Jan 2025 13:45:38 +0100
From: Niklas Söderlund <niklas.soderlund@...natech.se>
To: Paul Barker <paul.barker.ct@...renesas.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Sergey Shtylyov <s.shtylyov@....ru>, netdev@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net PATCH] net: ravb: Fix max TX frame size for RZ/V2M

Hi Paul,

Nice catch.

On 2025-01-09 11:37:06 +0000, Paul Barker wrote:
> When tx_max_frame_size was added to struct ravb_hw_info, no value was
> set in ravb_rzv2m_hw_info so the default value of zero was used.
> 
> The maximum MTU is set by subtracting from tx_max_frame_size to allow
> space for headers and frame checksums. As ndev->max_mtu is unsigned,
> this subtraction wraps around leading to a ridiculously large positive
> value that is obviously incorrect.
> 
> Before tx_max_frame_size was introduced, the maximum MTU was based on
> rx_max_frame_size. So, we can restore the correct maximum MTU by copying
> the rx_max_frame_size value into tx_max_frame_size for RZ/V2M.
> 
> Fixes: 1d63864299ca ("net: ravb: Fix maximum TX frame size for GbEth devices")
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

> ---
>  drivers/net/ethernet/renesas/ravb_main.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index ac0f093f647a..bc395294a32d 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -2763,6 +2763,7 @@ static const struct ravb_hw_info ravb_rzv2m_hw_info = {
>  	.net_features = NETIF_F_RXCSUM,
>  	.stats_len = ARRAY_SIZE(ravb_gstrings_stats),
>  	.tccr_mask = TCCR_TSRQ0 | TCCR_TSRQ1 | TCCR_TSRQ2 | TCCR_TSRQ3,
> +	.tx_max_frame_size = SZ_2K,
>  	.rx_max_frame_size = SZ_2K,
>  	.rx_buffer_size = SZ_2K +
>  			  SKB_DATA_ALIGN(sizeof(struct skb_shared_info)),
> 
> base-commit: 2d2d4f60ed266a8f340a721102d035252606980b
> -- 
> 2.39.5
> 

-- 
Kind Regards,
Niklas Söderlund