netdev - Re: [PATCH net-next v4 09/13] net: wwan: t7xx: Add WWAN network interface

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Date:   Thu, 10 Feb 2022 12:45:04 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Ricardo Martinez <ricardo.martinez@...ux.intel.com>
cc:     Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        m.chetan.kumar@...el.com, chandrashekar.devegowda@...el.com,
        linuxwwan@...el.com, chiranjeevi.rapolu@...ux.intel.com,
        haijun.liu@...iatek.com, amir.hanania@...el.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        dinesh.sharma@...el.com, eliot.lee@...el.com,
        moises.veleta@...el.com, pierre-louis.bossart@...el.com,
        muralidharan.sethuraman@...el.com, Soumya.Prakash.Mishra@...el.com,
        sreehari.kancharla@...el.com
Subject: Re: [PATCH net-next v4 09/13] net: wwan: t7xx: Add WWAN network
 interface

On Thu, 13 Jan 2022, Ricardo Martinez wrote:

> From: Haijun Liu <haijun.liu@...iatek.com>
> 
> Creates the Cross Core Modem Network Interface (CCMNI) which implements
> the wwan_ops for registration with the WWAN framework, CCMNI also
> implements the net_device_ops functions used by the network device.
> Network device operations include open, close, start transmission, TX
> timeout, change MTU, and select queue.
> 
> Signed-off-by: Haijun Liu <haijun.liu@...iatek.com>
> Co-developed-by: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
> Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
> Co-developed-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> Signed-off-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> ---

> +static int t7xx_ccmni_open(struct net_device *dev)
> +{
> +	struct t7xx_ccmni *ccmni = wwan_netdev_drvpriv(dev);
> +
> +	netif_carrier_on(dev);
> +	netif_tx_start_all_queues(dev);
> +	atomic_inc(&ccmni->usage);
> +	return 0;
> +}
> +
> +static int t7xx_ccmni_close(struct net_device *dev)
> +{
> +	struct t7xx_ccmni *ccmni = wwan_netdev_drvpriv(dev);
> +
> +	if (atomic_dec_return(&ccmni->usage) < 0)
> +		return -EINVAL;

I'm certainly way out of my expertize here in knowing how/when these open 
and close can be called. That kept in mind, I wonder if there's need to do 
rollback for the atomic dec.

> +static void t7xx_ccmni_wwan_setup(struct net_device *dev)
> +{
> +	dev->header_ops = NULL;
> +	dev->hard_header_len += sizeof(struct ccci_header);
> +
> +	dev->mtu = ETH_DATA_LEN;
> +	dev->max_mtu = CCMNI_MTU_MAX;
> +	dev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
> +	dev->watchdog_timeo = CCMNI_NETDEV_WDT_TO;
> +	/* CCMNI is a pure IP device */
> +	dev->flags = IFF_POINTOPOINT | IFF_NOARP;
> +
> +	/* Not supporting VLAN */
> +	dev->features = NETIF_F_VLAN_CHALLENGED;
> +
> +	dev->features |= NETIF_F_SG;
> +	dev->hw_features |= NETIF_F_SG;
> +
> +	/* Uplink checksum offload */
> +	dev->features |= NETIF_F_HW_CSUM;
> +	dev->hw_features |= NETIF_F_HW_CSUM;
> +
> +	/* Downlink checksum offload */
> +	dev->features |= NETIF_F_RXCSUM;
> +	dev->hw_features |= NETIF_F_RXCSUM;
> +
> +	/* Use kernel default free_netdev() function */
> +	dev->needs_free_netdev = true;
> +
> +	/* No need to free again because of free_netdev() */
> +	dev->priv_destructor = NULL;

Isn't the struct zeroed for you?

Maybe some of those comments are not that useful?


> +	ctlb->capability = NIC_CAP_TXBUSY_STOP | NIC_CAP_SGIO |
> +			   NIC_CAP_DATA_ACK_DVD | NIC_CAP_CCMNI_MQ;

Is capability going to remain constant? And some of these are
not used at all.

Related to this, e.g., the NETIF_F_SG setting above doesn't seem to care 
about what is in capability (assuming SGIO means what I think it does),
should it?

> +	/* WWAN core will create a netdev for the default IP MUX channel */
> +	ret = wwan_register_ops(dev, &ccmni_wwan_ops, ctlb, IP_MUX_SESSION_DEFAULT);
> +	if (ret)
> +		goto err_unregister_ops;
> +
> +	init_md_status_notifier(t7xx_dev);
> +
> +	return 0;
> +
> +err_unregister_ops:
> +	wwan_unregister_ops(dev);

If wwan_register_ops fails, why is wwan_unregister_ops needed?

> +/* Must be less than DPMAIF_HW_MTU_SIZE (3*1024 + 8) */

This could be enforced with BUILD_BUG_ON if you want.


-- 
 i.