linux-kernel - 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 10:18:16 +0100
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Sanjuán García, Jorge
	<Jorge.SanjuanGarcia@...gon.com>
CC: "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>,
	"s-vadapalli@...com" <s-vadapalli@...com>, "grygorii.strashko@...com"
	<grygorii.strashko@...com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v2 1/1] net: ethernet: ti: am65-cpsw: Fix max mtu to
 fit ethernet frames

The 01/05/2024 08:55, 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>

In case you send a single patch then, it is not required to create a
cover letter. Other then that it looks OK.

Reviewed-by: Horatiu Vultur <horatiu.vultur@...rochip.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 |
> --
> 2.34.1
> 

-- 
/Horatiu