Re: [PATCH for-next 4/4] RDMA/erdma: Support dynamic mtu

[Leon Romanovsky <leon@kernel.org>]

On Fri, Sep 09, 2022 at 05:38:22PM +0800, Cheng Xu wrote:
> Hardware now support jumbo frame for RDMA. So we introduce a new CMDQ
> message to support mtu change notification.
> 
> Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
> ---
>  drivers/infiniband/hw/erdma/erdma.h       |  1 +
>  drivers/infiniband/hw/erdma/erdma_hw.h    |  6 ++++++
>  drivers/infiniband/hw/erdma/erdma_main.c  |  8 +++++++-
>  drivers/infiniband/hw/erdma/erdma_verbs.c | 11 +++++++++++
>  drivers/infiniband/hw/erdma/erdma_verbs.h |  1 +
>  5 files changed, 26 insertions(+), 1 deletion(-)

<...>

> --- a/drivers/infiniband/hw/erdma/erdma_main.c
> +++ b/drivers/infiniband/hw/erdma/erdma_main.c
> @@ -34,10 +34,15 @@ static int erdma_netdev_event(struct notifier_block *nb, unsigned long event,
>  		dev->state = IB_PORT_DOWN;
>  		erdma_port_event(dev, IB_EVENT_PORT_ERR);
>  		break;
> +	case NETDEV_CHANGEMTU:
> +		if (dev->mtu != netdev->mtu) {
> +			erdma_set_mtu(dev, netdev->mtu);
> +			dev->mtu = netdev->mtu;
> +		}
> +		break;
>  	case NETDEV_REGISTER:
>  	case NETDEV_UNREGISTER:
>  	case NETDEV_CHANGEADDR:
> -	case NETDEV_CHANGEMTU:
>  	case NETDEV_GOING_DOWN:
>  	case NETDEV_CHANGE:
>  	default:
> @@ -95,6 +100,7 @@ static int erdma_device_register(struct erdma_dev *dev)
>  	if (ret)
>  		return ret;
>  
> +	dev->mtu = dev->netdev->mtu;
>  	addrconf_addr_eui48((u8 *)&ibdev->node_guid, dev->netdev->dev_addr);
>  
>  	ret = ib_register_device(ibdev, "erdma_%d", &dev->pdev->dev);
> diff --git a/drivers/infiniband/hw/erdma/erdma_verbs.c b/drivers/infiniband/hw/erdma/erdma_verbs.c
> index aea93d08af95..62be98e2b941 100644
> --- a/drivers/infiniband/hw/erdma/erdma_verbs.c
> +++ b/drivers/infiniband/hw/erdma/erdma_verbs.c
> @@ -1436,6 +1436,17 @@ int erdma_create_cq(struct ib_cq *ibcq, const struct ib_cq_init_attr *attr,
>  	return ret;
>  }
>  
> +void erdma_set_mtu(struct erdma_dev *dev, u32 mtu)
> +{
> +	struct erdma_cmdq_config_mtu_req req;
> +
> +	erdma_cmdq_build_reqhdr(&req.hdr, CMDQ_SUBMOD_COMMON,
> +				CMDQ_OPCODE_CONF_MTU);
> +	req.mtu = mtu;
> +
> +	erdma_post_cmd_wait(&dev->cmdq, &req, sizeof(req), NULL, NULL);
> +}

I don't see any backward compatibility here. How can you make sure that
new code that supports MTU change works correctly on old FW/device?

Thanks