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SubjectRe: [PATCH net-next] net: hns3: Add support to change MTU in hardware & netdev
On Fri, Aug 18, 2017 at 12:35:58PM +0100, Salil Mehta wrote:
> This patch adds the following support to the HNS3 driver:
> 1. Support to change the Maximum Transmission Unit of a
> netdevice and of a port in hardware .
> 2. Initializes the supported MTU range for the netdevice.
>
> Signed-off-by: lipeng <lipeng321@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
> .../net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c | 46 ++++++++++++++++++++++
> .../net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.h | 1 +
> 2 files changed, 47 insertions(+)
>
> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c
> index e731f87..8e3711e 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.c
> @@ -1278,11 +1278,53 @@ static int hns3_ndo_set_vf_vlan(struct net_device *netdev, int vf, u16 vlan,
> return ret;
> }
>
> +static int hns3_nic_change_mtu(struct net_device *netdev, int new_mtu)
> +{
> + struct hns3_nic_priv *priv = netdev_priv(netdev);
> + struct hnae3_handle *h = priv->ae_handle;
> + bool if_running = netif_running(netdev);
> + int ret;
> +
> + /* no change in MTU */
> + if (new_mtu == netdev->mtu)
> + return 0;

Hi Salil

It is worth reading the core code:

http://elixir.free-electrons.com/linux/latest/source/net/core/dev.c#L6713

+
> + if (!h->ae_algo->ops->set_mtu)
> + return -ENOTSUPP;
> +
> + /* if this was called with netdev up then bring netdevice down */
> + if (if_running) {
> + (void)hns3_nic_net_stop(netdev);
> + msleep(100);
> + }
> +
> + ret = h->ae_algo->ops->set_mtu(h, new_mtu);
> + if (ret) {
> + netdev_err(netdev, "failed to change MTU in hardware %d\n",
> + ret);
> + return ret;
> + }
> +
> + /* assign newly changed mtu to netdevice as well */
> + netdev->mtu = new_mtu;

http://elixir.free-electrons.com/linux/latest/source/net/core/dev.c#L6698

> +
> + /* if the netdev was running earlier, bring it up again */
> + if (if_running) {
> + if (hns3_nic_net_open(netdev)) {
> + netdev_err(netdev, "MTU, couldnt up netdev again\n");
> + ret = -EINVAL;
> + }
> + }
> +
> + return ret;
> +}
> +
> static const struct net_device_ops hns3_nic_netdev_ops = {
> .ndo_open = hns3_nic_net_open,
> .ndo_stop = hns3_nic_net_stop,
> .ndo_start_xmit = hns3_nic_net_xmit,
> .ndo_set_mac_address = hns3_nic_net_set_mac_address,
> + .ndo_change_mtu = hns3_nic_change_mtu,
> .ndo_set_features = hns3_nic_set_features,
> .ndo_get_stats64 = hns3_nic_get_stats64,
> .ndo_setup_tc = hns3_nic_setup_tc,
> @@ -2752,6 +2794,10 @@ static int hns3_client_init(struct hnae3_handle *handle)
> goto out_reg_netdev_fail;
> }
>
> + /* MTU range: 68 - 9706 */
> + netdev->min_mtu = ETH_MIN_MTU;

http://elixir.free-electrons.com/linux/latest/source/net/ethernet/eth.c#L361

> + netdev->max_mtu = HNS3_MAX_MTU - (ETH_HLEN + ETH_FCS_LEN + VLAN_HLEN);
> +
> return ret;
>
> out_reg_netdev_fail:
> diff --git a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.h b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.h
> index a6e8f15..7e87461 100644
> --- a/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.h
> +++ b/drivers/net/ethernet/hisilicon/hns3/hns3pf/hns3_enet.h
> @@ -76,6 +76,7 @@ enum hns3_nic_state {
> #define HNS3_RING_NAME_LEN 16
> #define HNS3_BUFFER_SIZE_2048 2048
> #define HNS3_RING_MAX_PENDING 32768
> +#define HNS3_MAX_MTU 9728

It seems odd that it does not already exists somewhere. The core does
not enforce the MTU. You could be passed a frame which is bigger. So
you should check before trying to pass something to the hardware which
the hardware cannot handle.

Andrew

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