netdev - Re: [PATCH net v2 1/1] net: ethernet: ti: am65-cpsw: Fix max mtu to fit ethernet frames

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Date: Thu, 11 Jan 2024 15:16:27 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Sanjuán García, Jorge
	<Jorge.SanjuanGarcia@...gon.com>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com"
	<edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        <s-vadapalli@...com>
Subject: Re: [PATCH net v2 1/1] net: ethernet: ti: am65-cpsw: Fix max mtu to
 fit ethernet frames



On 05/01/24 14:25, Sanjuán García, Jorge wrote:
> The value of AM65_CPSW_MAX_PACKET_SIZE represents the maximum length
> of a received frame. This value is written to the register
> AM65_CPSW_PORT_REG_RX_MAXLEN.
> 
> The maximum MTU configured on the network device should then leave
> some room for the ethernet headers and frame check. Otherwise, if
> the network interface is configured to its maximum mtu possible,
> the frames will be larger than AM65_CPSW_MAX_PACKET_SIZE and will
> get dropped as oversized.
> 
> The switch supports ethernet frame sizes between 64 and 2024 bytes
> (including VLAN) as stated in the technical reference manual, so
> define AM65_CPSW_MAX_PACKET_SIZE with that maximum size.
> 
> Fixes: 93a76530316a ("net: ethernet: ti: introduce am65x/j721e gigabit eth 
> subsystem driver")
> Signed-off-by: Jorge Sanjuan Garcia <jorge.sanjuangarcia@...gon.com>

Reviewed-by: Siddharth Vadapalli <s-vadapalli@...com>

> ---
>   drivers/net/ethernet/ti/am65-cpsw-nuss.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c 
> b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> index 7651f90f51f2..3c7854537cb5 100644
> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> @@ -56,7 +56,7 @@
>   #define AM65_CPSW_MAX_PORTS     8
> 
>   #define AM65_CPSW_MIN_PACKET_SIZE       VLAN_ETH_ZLEN
> -#define AM65_CPSW_MAX_PACKET_SIZE      (VLAN_ETH_FRAME_LEN + ETH_FCS_LEN)
> +#define AM65_CPSW_MAX_PACKET_SIZE      2024
> 
>   #define AM65_CPSW_REG_CTL               0x004
>   #define AM65_CPSW_REG_STAT_PORT_EN      0x014
> @@ -2196,7 +2196,8 @@ am65_cpsw_nuss_init_port_ndev(struct am65_cpsw_common 
> *common, u32 port_idx)
>           eth_hw_addr_set(port->ndev, port->slave.mac_addr);
> 
>           port->ndev->min_mtu = AM65_CPSW_MIN_PACKET_SIZE;
> -       port->ndev->max_mtu = AM65_CPSW_MAX_PACKET_SIZE;
> +       port->ndev->max_mtu = AM65_CPSW_MAX_PACKET_SIZE -
> +                             (VLAN_ETH_HLEN + ETH_FCS_LEN);
>           port->ndev->hw_features = NETIF_F_SG |
>                                     NETIF_F_RXCSUM |
>                                     NETIF_F_HW_CSUM |

...

-- 
Regards,
Siddharth.