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Date:   Thu, 15 Oct 2020 12:33:42 +0200
From:   Loic Poulain <loic.poulain@...aro.org>
To:     davem@...emloft.net, Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Hemant Kumar <hemantk@...eaurora.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v4 1/2] net: Add mhi-net driver

Please ignore this one, the title is wrong (it's not patch 1/2).


On Thu, 15 Oct 2020 at 12:25, Loic Poulain <loic.poulain@...aro.org> 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>
> ---
>   v2: - rebase on net-next
>       - remove useless skb_linearize
>       - check error type on mhi_queue return
>       - rate limited errors
>       - Schedule RX refill only on 'low' buf level
>       - SET_NETDEV_DEV in probe
>       - reorder device remove sequence
>   v3: - Stop channels on net_register error
>       - Remove useles parentheses
>       - Add driver .owner
>   v4: - prevent potential cpu hog in rx-refill loop
>       - Access mtu via READ_ONCE
>
>  drivers/net/Kconfig   |   7 ++
>  drivers/net/Makefile  |   1 +
>  drivers/net/mhi_net.c | 289 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 297 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..fe605a4
> --- /dev/null
> +++ b/drivers/net/mhi_net.c
> @@ -0,0 +1,289 @@
> +// 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;
> +       u32 rx_queue_sz;
> +};
> +
> +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;
> +
> +       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 == -ENOMEM) {
> +               netif_stop_queue(ndev);
> +               return NETDEV_TX_BUSY;
> +       } else if (unlikely(err)) {
> +               net_err_ratelimited("%s: Failed to queue TX buf (%d)\n",
> +                                   ndev->name, err);
> +               mhi_netdev->stats.tx_dropped++;
> +               kfree_skb(skb);
> +       }
> +
> +       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_POINTOPOINT | IFF_NOARP;
> +       ndev->netdev_ops = &mhi_netdev_ops;
> +       ndev->mtu = DEFAULT_MTU;
> +       ndev->min_mtu = MIN_MTU;
> +       ndev->max_mtu = MAX_MTU;
> +       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;
> +       int remaining;
> +
> +       remaining = atomic_dec_return(&mhi_netdev->stats.rx_queued);
> +
> +       if (unlikely(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);
> +       }
> +
> +       /* Refill if RX buffers queue becomes low */
> +       if (remaining <= mhi_netdev->rx_queue_sz / 2)
> +               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;
> +       int size = READ_ONCE(ndev->mtu);
> +       struct sk_buff *skb;
> +       int err;
> +
> +       do {
> +               skb = netdev_alloc_skb(ndev, size);
> +               if (unlikely(!skb))
> +                       break;
> +
> +               err = mhi_queue_skb(mdev, DMA_FROM_DEVICE, skb, size, MHI_EOT);
> +               if (err) {
> +                       if (unlikely(err != -ENOMEM))
> +                               net_err_ratelimited("%s: Failed to queue RX buf (%d)\n",
> +                                                   ndev->name, err);
> +                       kfree_skb(skb);
> +                       break;
> +               }
> +
> +               atomic_inc(&mhi_netdev->stats.rx_queued);
> +
> +               /* Do not hog the CPU if rx buffers are completed faster than
> +                * queued (unlikely).
> +                */
> +               cond_resched();
> +       } while (1);
> +
> +       /* If we're still starved of rx buffers, reschedule latter */
> +       if (unlikely(!atomic_read(&mhi_netdev->stats.rx_queued)))
> +               schedule_delayed_work(&mhi_netdev->rx_refill, HZ / 2);
> +}
> +
> +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)
> +               return -ENOMEM;
> +
> +       mhi_netdev = netdev_priv(ndev);
> +       dev_set_drvdata(dev, mhi_netdev);
> +       mhi_netdev->ndev = ndev;
> +       mhi_netdev->mdev = mhi_dev;
> +       SET_NETDEV_DEV(ndev, &mhi_dev->dev);
> +
> +       /* All MHI net channels have 128 ring elements (at least for now) */
> +       mhi_netdev->rx_queue_sz = 128;
> +
> +       INIT_DELAYED_WORK(&mhi_netdev->rx_refill, mhi_net_rx_refill_work);
> +
> +       /* Start MHI channels */
> +       err = mhi_prepare_for_transfer(mhi_dev);
> +       if (err)
> +               goto out_err;
> +
> +       err = register_netdev(ndev);
> +       if (err) {
> +               mhi_unprepare_from_transfer(mhi_dev);
> +               goto out_err;
> +       }
> +
> +       return 0;
> +
> +out_err:
> +       free_netdev(ndev);
> +       return err;
> +}
> +
> +static void mhi_net_remove(struct mhi_device *mhi_dev)
> +{
> +       struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev->dev);
> +
> +       unregister_netdev(mhi_netdev->ndev);
> +
> +       mhi_unprepare_from_transfer(mhi_netdev->mdev);
> +
> +       free_netdev(mhi_netdev->ndev);
> +}
> +
> +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",
> +               .owner = THIS_MODULE,
> +       },
> +};
> +
> +module_mhi_driver(mhi_net_driver);
> +
> +MODULE_AUTHOR("Loic Poulain <loic.poulain@...aro.org>");
> +MODULE_DESCRIPTION("Network over MHI");
> +MODULE_LICENSE("GPL v2");
> --
> 2.7.4
>

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