linux-kernel - Re: [PATCH net-next v2 1/1] net: macb: fix negative max

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Message-ID: <de66722b-9832-e9dc-008a-5baece0c7afa@microchip.com>
Date:   Fri, 17 Jun 2022 07:27:03 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <o.rempel@...gutronix.de>, <Nicolas.Ferre@...rochip.com>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>
CC:     <kernel@...gutronix.de>, <linux-kernel@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/1] net: macb: fix negative max_mtu size for
 sama5d3

On 17.06.2022 10:16, Oleksij Rempel wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> JML register on probe will return zero . This register is configured
> later on macb_init_hw() which is called on open.
> Since we have zero, after header and FCS length subtraction we will get
> negative max_mtu size. This issue was affecting DSA drivers with MTU support
> (for example KSZ9477).
> 
> Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>

Reviewed-by: Claudiu Beznea <claudiu.beznea@...rochip.com>


> ---
> changes v2:
> - properly describe fail reason
> - simplify max_mtu logic
> 
>  drivers/net/ethernet/cadence/macb_main.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index d89098f4ede8..d0ea8dbfa213 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -4913,8 +4913,8 @@ static int macb_probe(struct platform_device *pdev)
> 
>         /* MTU range: 68 - 1500 or 10240 */
>         dev->min_mtu = GEM_MTU_MIN_SIZE;
> -       if (bp->caps & MACB_CAPS_JUMBO)
> -               dev->max_mtu = gem_readl(bp, JML) - ETH_HLEN - ETH_FCS_LEN;
> +       if ((bp->caps & MACB_CAPS_JUMBO) && bp->jumbo_max_len)
> +               dev->max_mtu = bp->jumbo_max_len - ETH_HLEN - ETH_FCS_LEN;
>         else
>                 dev->max_mtu = ETH_DATA_LEN;
> 
> --
> 2.30.2
>