netdev - Re: [PATCH v2] sh_eth: add support to change MTU

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Date:   Fri, 9 Jun 2017 22:36:58 +0200
From:   "Niklas Söderlund" <niklas.soderlund@...natech.se>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:     netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v2] sh_eth: add support to change MTU

On 2017-06-09 22:32:15 +0200, Niklas Söderlund wrote:
> The hardware supports the MTU to be changed and the driver it self is
> somewhat prepared to support this. This patch hooks up the callbacks to
> be able to change the MTU from user-space.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> Acked-by: Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
> ---
> 
> Based on v4.12-rc1 and tested on Renesas R-Car Koelsch M2.
> 
> Test procedure:
> 
> 1. On host set MTU to something large (9000) was used for this test.
> 
> 2. On target set MTU to something other then 1500, in this test the max
>    MTU of 1978 is used.
> 
> 3. Send ping with large payload and observe that it works.
> 
>    ping -M do -s 1954 <target>
> 
>    The reason for 1954 instead of 1982 is two fold:
> 
>    1. On Linux (different on Mac IIRC) the ICMP/ping implementation
>       doesn’t encapsulate the 28 byte ICMP (8) + IP (20).
>    2. The driver internally reserve 4 bytes of transmission buffer for
>       an optional VLAN header (4). And since no VLAN is used in this
>       setup the additional 4 bytes can carry data.
> 
> 4. For extra verification the packet flow is inspected using tcpdump to
>    verify that there is no packet fragmentation.
> 
> * Changes since v1
> - Fix spelling mistake in comment, thanks Sergei!
> - Add Acked-by from Sergei.
> 
>  drivers/net/ethernet/renesas/sh_eth.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
> index f68c4db656eda846..9c6e4025bfc9f5c5 100644
> --- a/drivers/net/ethernet/renesas/sh_eth.c
> +++ b/drivers/net/ethernet/renesas/sh_eth.c
> @@ -2558,6 +2558,17 @@ static int sh_eth_do_ioctl(struct net_device *ndev, struct ifreq *rq, int cmd)
>  	return phy_mii_ioctl(phydev, rq, cmd);
>  }
>  
> +static int sh_eth_change_mtu(struct net_device *dev, int new_mtu)
> +{
> +	if (netif_running(dev))
> +		return -EBUSY;
> +
> +	dev->mtu = new_mtu;
> +	netdev_update_features(dev);
> +
> +	return 0;
> +}
> +
>  /* For TSU_POSTn. Please refer to the manual about this (strange) bitfields */
>  static void *sh_eth_tsu_get_post_reg_offset(struct sh_eth_private *mdp,
>  					    int entry)
> @@ -3029,6 +3040,7 @@ static const struct net_device_ops sh_eth_netdev_ops = {
>  	.ndo_set_rx_mode	= sh_eth_set_rx_mode,
>  	.ndo_tx_timeout		= sh_eth_tx_timeout,
>  	.ndo_do_ioctl		= sh_eth_do_ioctl,
> +	.ndo_change_mtu		= sh_eth_change_mtu,
>  	.ndo_validate_addr	= eth_validate_addr,
>  	.ndo_set_mac_address	= eth_mac_addr,
>  };
> @@ -3043,6 +3055,7 @@ static const struct net_device_ops sh_eth_netdev_ops_tsu = {
>  	.ndo_vlan_rx_kill_vid	= sh_eth_vlan_rx_kill_vid,
>  	.ndo_tx_timeout		= sh_eth_tx_timeout,
>  	.ndo_do_ioctl		= sh_eth_do_ioctl,
> +	.ndo_change_mtu		= sh_eth_change_mtu,
>  	.ndo_validate_addr	= eth_validate_addr,
>  	.ndo_set_mac_address	= eth_mac_addr,
>  };
> @@ -3171,6 +3184,13 @@ static int sh_eth_drv_probe(struct platform_device *pdev)
>  	}
>  	sh_eth_set_default_cpu_data(mdp->cd);
>  
> +	/* User's manua states max MTU should be 2048 but due to the

s/manua/manual/

Do I need to resend or can this be fixed up when applying? Sorry for 
this.

> +	 * alignment calculations in sh_eth_ring_init() the practical
> +	 * MTU is a bit less. Maybe this can be optimized some more.
> +	 */
> +	ndev->max_mtu = 2000 - (ETH_HLEN + VLAN_HLEN + ETH_FCS_LEN);
> +	ndev->min_mtu = ETH_MIN_MTU;
> +
>  	/* set function */
>  	if (mdp->cd->tsu)
>  		ndev->netdev_ops = &sh_eth_netdev_ops_tsu;
> -- 
> 2.13.1
> 

-- 
Regards,
Niklas Söderlund