Date:   Mon, 12 Oct 2020 09:34:20 -0500
From:   Dan Williams <dcbw@...hat.com>
To:     Loic Poulain <loic.poulain@...aro.org>, davem@...emloft.net,
        hemantk@...eaurora.org
Cc:     netdev@...r.kernel.org, manivannan.sadhasivam@...aro.org
Subject: Re: [PATCH] net: Add mhi-net driver

On Fri, 2020-10-09 at 22:33 +0200, Loic Poulain wrote:
> This patch adds a new network driver implementing MHI transport for
> network packets. Packets can be in any format, though QMAP (rmnet)
> is the usual protocol (flow control + PDN mux).
> 
> It support two MHI devices, IP_HW0 which is, the path to the IPA
> (IP accelerator) on qcom modem, And IP_SW0 which is the software
> driven IP path (to modem CPU).
> 
> Signed-off-by: Loic Poulain <loic.poulain@...aro.org>
> ---
>  drivers/net/Kconfig   |   7 ++
>  drivers/net/Makefile  |   1 +
>  drivers/net/mhi_net.c | 281
> ++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 289 insertions(+)
>  create mode 100644 drivers/net/mhi_net.c
> 
> diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
> index 1368d1d..11a6357 100644
> --- a/drivers/net/Kconfig
> +++ b/drivers/net/Kconfig
> @@ -426,6 +426,13 @@ config VSOCKMON
>  	  mostly intended for developers or support to debug vsock
> issues. If
>  	  unsure, say N.
>  
> +config MHI_NET
> +	tristate "MHI network driver"
> +	depends on MHI_BUS
> +	help
> +	  This is the network driver for MHI.  It can be used with
> +	  QCOM based WWAN modems (like SDX55).  Say Y or M.
> +
>  endif # NET_CORE
>  
>  config SUNGEM_PHY
> diff --git a/drivers/net/Makefile b/drivers/net/Makefile
> index 94b6080..8312037 100644
> --- a/drivers/net/Makefile
> +++ b/drivers/net/Makefile
> @@ -34,6 +34,7 @@ obj-$(CONFIG_GTP) += gtp.o
>  obj-$(CONFIG_NLMON) += nlmon.o
>  obj-$(CONFIG_NET_VRF) += vrf.o
>  obj-$(CONFIG_VSOCKMON) += vsockmon.o
> +obj-$(CONFIG_MHI_NET) += mhi_net.o
>  
>  #
>  # Networking Drivers
> diff --git a/drivers/net/mhi_net.c b/drivers/net/mhi_net.c
> new file mode 100644
> index 0000000..f66248e
> --- /dev/null
> +++ b/drivers/net/mhi_net.c
> @@ -0,0 +1,281 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/* MHI Network driver - Network over MHI
> + *
> + * Copyright (C) 2020 Linaro Ltd <loic.poulain@...aro.org>
> + */
> +
> +#include <linux/if_arp.h>
> +#include <linux/mhi.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/netdevice.h>
> +#include <linux/skbuff.h>
> +
> +#define MIN_MTU		ETH_MIN_MTU
> +#define MAX_MTU		0xffff
> +#define DEFAULT_MTU	8192
> +
> +struct mhi_net_stats {
> +	u64 rx_packets;
> +	u64 rx_bytes;
> +	u64 rx_errors;
> +	u64 rx_dropped;
> +	u64 tx_packets;
> +	u64 tx_bytes;
> +	u64 tx_errors;
> +	u64 tx_dropped;
> +	atomic_t rx_queued;
> +};
> +
> +struct mhi_net_dev {
> +	struct mhi_device *mdev;
> +	struct net_device *ndev;
> +	struct delayed_work rx_refill;
> +	struct mhi_net_stats stats;
> +};
> +
> +static int mhi_ndo_open(struct net_device *ndev)
> +{
> +	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
> +
> +	/* Feed the rx buffer pool */
> +	schedule_delayed_work(&mhi_netdev->rx_refill, 0);
> +
> +	/* Carrier is established via out-of-band channel (e.g. qmi) */
> +	netif_carrier_on(ndev);
> +
> +	netif_start_queue(ndev);
> +
> +	return 0;
> +}
> +
> +static int mhi_ndo_stop(struct net_device *ndev)
> +{
> +	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
> +
> +	netif_stop_queue(ndev);
> +	netif_carrier_off(ndev);
> +	cancel_delayed_work_sync(&mhi_netdev->rx_refill);
> +
> +	return 0;
> +}
> +
> +static int mhi_ndo_xmit(struct sk_buff *skb, struct net_device
> *ndev)
> +{
> +	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
> +	struct mhi_device *mdev = mhi_netdev->mdev;
> +	int err;
> +
> +	/* Only support for single buffer transfer for now */
> +	err = skb_linearize(skb);
> +	if (unlikely(err)) {
> +		kfree_skb(skb);
> +		mhi_netdev->stats.tx_dropped++;
> +		return NETDEV_TX_OK;
> +	}
> +
> +	skb_tx_timestamp(skb);
> +
> +	/* mhi_queue_skb is not thread-safe, but xmit is serialized by
> the
> +	 * network core. Once MHI core will be thread save, migrate to
> +	 * NETIF_F_LLTX support.
> +	 */
> +	err = mhi_queue_skb(mdev, DMA_TO_DEVICE, skb, skb->len,
> MHI_EOT);
> +	if (err) {
> +		netdev_err(ndev, "mhi_queue_skb err %d\n", err);
> +		netif_stop_queue(ndev);
> +		return (err == -ENOMEM) ? NETDEV_TX_BUSY : err;
> +	}
> +
> +	return NETDEV_TX_OK;
> +}
> +
> +static void mhi_ndo_get_stats64(struct net_device *ndev,
> +				struct rtnl_link_stats64 *stats)
> +{
> +	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
> +
> +	stats->rx_packets = mhi_netdev->stats.rx_packets;
> +	stats->rx_bytes = mhi_netdev->stats.rx_bytes;
> +	stats->rx_errors = mhi_netdev->stats.rx_errors;
> +	stats->rx_dropped = mhi_netdev->stats.rx_dropped;
> +	stats->tx_packets = mhi_netdev->stats.tx_packets;
> +	stats->tx_bytes = mhi_netdev->stats.tx_bytes;
> +	stats->tx_errors = mhi_netdev->stats.tx_errors;
> +	stats->tx_dropped = mhi_netdev->stats.tx_dropped;
> +}
> +
> +static const struct net_device_ops mhi_netdev_ops = {
> +	.ndo_open               = mhi_ndo_open,
> +	.ndo_stop               = mhi_ndo_stop,
> +	.ndo_start_xmit         = mhi_ndo_xmit,
> +	.ndo_get_stats64	= mhi_ndo_get_stats64,
> +};
> +
> +static void mhi_net_setup(struct net_device *ndev)
> +{
> +	ndev->header_ops = NULL;  /* No header */
> +	ndev->type = ARPHRD_NONE; /* QMAP... */
> +	ndev->hard_header_len = 0;
> +	ndev->addr_len = 0;
> +	ndev->flags &= ~(IFF_BROADCAST | IFF_MULTICAST);
> +	ndev->netdev_ops = &mhi_netdev_ops;
> +	ndev->mtu = DEFAULT_MTU;
> +	ndev->min_mtu = MIN_MTU;
> +	ndev->max_mtu = MAX_MTU;
> +	ndev->needs_free_netdev = true;
> +	ndev->tx_queue_len = 1000;
> +}
> +
> +static void mhi_net_dl_callback(struct mhi_device *mhi_dev,
> +				struct mhi_result *mhi_res)
> +{
> +	struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev-
> >dev);
> +	struct sk_buff *skb = mhi_res->buf_addr;
> +
> +	atomic_dec(&mhi_netdev->stats.rx_queued);
> +
> +	if (mhi_res->transaction_status) {
> +		mhi_netdev->stats.rx_errors++;
> +		kfree_skb(skb);
> +	} else {
> +		mhi_netdev->stats.rx_packets++;
> +		mhi_netdev->stats.rx_bytes += mhi_res->bytes_xferd;
> +
> +		skb->protocol = htons(ETH_P_MAP);
> +		skb_put(skb, mhi_res->bytes_xferd);
> +		netif_rx(skb);
> +	}
> +
> +	schedule_delayed_work(&mhi_netdev->rx_refill, 0);
> +}
> +
> +static void mhi_net_ul_callback(struct mhi_device *mhi_dev,
> +				struct mhi_result *mhi_res)
> +{
> +	struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev-
> >dev);
> +	struct net_device *ndev = mhi_netdev->ndev;
> +	struct sk_buff *skb = mhi_res->buf_addr;
> +
> +	/* Hardware has consumed the buffer, so free the skb (which is
> not
> +	 * freed by the MHI stack) and perform accounting.
> +	 */
> +	consume_skb(skb);
> +
> +	if (unlikely(mhi_res->transaction_status)) {
> +		mhi_netdev->stats.tx_errors++;
> +	} else {
> +		mhi_netdev->stats.tx_packets++;
> +		mhi_netdev->stats.tx_bytes += mhi_res->bytes_xferd;
> +	}
> +
> +	if (netif_queue_stopped(ndev))
> +		netif_wake_queue(ndev);
> +}
> +
> +static void mhi_net_rx_refill_work(struct work_struct *work)
> +{
> +	struct mhi_net_dev *mhi_netdev = container_of(work, struct
> mhi_net_dev,
> +						      rx_refill.work);
> +	struct net_device *ndev = mhi_netdev->ndev;
> +	struct mhi_device *mdev = mhi_netdev->mdev;
> +	struct sk_buff *skb;
> +	int err;
> +
> +	if (!netif_running(ndev))
> +		return;
> +
> +	do {
> +		skb = netdev_alloc_skb(ndev, READ_ONCE(ndev->mtu));
> +		if (unlikely(!skb)) {
> +			/* If we are starved of RX buffers, retry later
> */
> +			if (!atomic_read(&mhi_netdev->stats.rx_queued))
> +				schedule_delayed_work(&mhi_netdev-
> >rx_refill, HZ / 2);
> +			break;
> +		}
> +
> +		err = mhi_queue_skb(mdev, DMA_FROM_DEVICE, skb, ndev-
> >mtu,
> +				    MHI_EOT);
> +		if (err) {
> +			atomic_dec(&mhi_netdev->stats.rx_queued);
> +			kfree_skb(skb);
> +			break;
> +		}
> +
> +		atomic_inc(&mhi_netdev->stats.rx_queued);
> +
> +	} while (1);
> +}
> +
> +static int mhi_net_probe(struct mhi_device *mhi_dev,
> +			 const struct mhi_device_id *id)
> +{
> +	const char *netname = (char *)id->driver_data;
> +	struct mhi_net_dev *mhi_netdev;
> +	struct net_device *ndev;
> +	struct device *dev = &mhi_dev->dev;
> +	int err;
> +
> +	ndev = alloc_netdev(sizeof(*mhi_netdev), netname,
> NET_NAME_PREDICTABLE,
> +			    mhi_net_setup);
> +	if (!ndev) {
> +		err = -ENOMEM;
> +		return err;
> +	}
> +
> +	mhi_netdev = netdev_priv(ndev);
> +	dev_set_drvdata(dev, mhi_netdev);
> +	mhi_netdev->ndev = ndev;
> +	mhi_netdev->mdev = mhi_dev;

SET_NETDEV_DEV(netdev, &mhi_dev->dev); ?

Let's at least set the sysfs links up right...

> +
> +	INIT_DELAYED_WORK(&mhi_netdev->rx_refill,
> mhi_net_rx_refill_work);
> +
> +	/* Start MHI channels */
> +	err = mhi_prepare_for_transfer(mhi_dev, 0);
> +	if (err) {
> +		free_netdev(ndev);
> +		return err;
> +	}
> +
> +	err = register_netdev(ndev);
> +	if (err) {
> +		dev_err(dev, "mhi_net: registering device failed\n");
> +		free_netdev(ndev);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static void mhi_net_remove(struct mhi_device *mhi_dev)
> +{
> +	struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev-
> >dev);
> +
> +	mhi_unprepare_from_transfer(mhi_netdev->mdev);
> +	unregister_netdev(mhi_netdev->ndev);
> +	/* netdev released from unregister */
> +}
> +
> +static const struct mhi_device_id mhi_net_id_table[] = {
> +	{ .chan = "IP_HW0", .driver_data = (kernel_ulong_t)"mhi_hwip%d"
> },
> +	{ .chan = "IP_SW0", .driver_data = (kernel_ulong_t)"mhi_swip%d"
> },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(mhi, mhi_net_id_table);
> +
> +static struct mhi_driver mhi_net_driver = {
> +	.probe = mhi_net_probe,
> +	.remove = mhi_net_remove,
> +	.dl_xfer_cb = mhi_net_dl_callback,
> +	.ul_xfer_cb = mhi_net_ul_callback,
> +	.id_table = mhi_net_id_table,
> +	.driver = {
> +		.name = "mhi_net",
> +	},
> +};
> +
> +module_mhi_driver(mhi_net_driver);
> +
> +MODULE_AUTHOR("Loic Poulain <loic.poulain@...aro.org>");
> +MODULE_DESCRIPTION("Network over MHI");
> +MODULE_LICENSE("GPL v2");

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