linux-kernel - Re: [PATCH net-next] net: hns3: Add support to change MTU in hardware & netdev

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Date:   Fri, 18 Aug 2017 18:01:57 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Salil Mehta <salil.mehta@...wei.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "Zhuangyuzeng (Yisen)" <yisen.zhuang@...wei.com>,
        "lipeng (Y)" <lipeng321@...wei.com>,
        "mehta.salil.lnk@...il.com" <mehta.salil.lnk@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH net-next] net: hns3: Add support to change MTU in
 hardware & netdev

> for example,
> file: drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
> static int init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>  
>  		netdev->priv_flags |= IFF_UNICAST_FLT;
>  
> +		/* MTU range: 81 - 9600 */
> +		netdev->min_mtu = 81; 
> +		netdev->max_mtu = MAX_MTU;

In this cause, the driver is not using the default values. So it sets
them.

Anyway, try it. After your alloc_etherdev_mqs(), print the value of
min_mtu. It should already be set to MIN_ETH_MTU.

> I see. IMHO HNS3 is currently limited by maximum buffer per descriptor
> which is 64k. I am sure such frames would get dropped in the hardware
> itself and which I guess should be more preferable than dropping in
> driver since it saves you some precious cpu cycles?

If you hardware handles this, then you don't need to do anything.

   Andrew