tilegx.c

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/*
 * Copyright 2012 Tilera Corporation. All Rights Reserved.
 *
 *   This program is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU General Public License
 *   as published by the Free Software Foundation, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/kernel.h>      /* printk() */
#include <linux/slab.h>        /* kmalloc() */
#include <linux/errno.h>       /* error codes */
#include <linux/types.h>       /* size_t */
#include <linux/interrupt.h>
#include <linux/in.h>
#include <linux/irq.h>
#include <linux/netdevice.h>   /* struct device, and other headers */
#include <linux/etherdevice.h> /* eth_type_trans */
#include <linux/skbuff.h>
#include <linux/ioctl.h>
#include <linux/cdev.h>
#include <linux/hugetlb.h>
#include <linux/in6.h>
#include <linux/timer.h>
#include <linux/hrtimer.h>
#include <linux/ktime.h>
#include <linux/io.h>
#include <linux/ctype.h>
#include <linux/ip.h>
#include <linux/tcp.h>

#include <asm/checksum.h>
#include <asm/homecache.h>
#include <gxio/mpipe.h>
#include <arch/sim.h>

/* Default transmit lockup timeout period, in jiffies. */
#define TILE_NET_TIMEOUT (5 * HZ)

/* The maximum number of distinct channels (idesc.channel is 5 bits). */
#define TILE_NET_CHANNELS 32

/* Maximum number of idescs to handle per "poll". */
#define TILE_NET_BATCH 128

/* Maximum number of packets to handle per "poll". */
#define TILE_NET_WEIGHT 64

/* Number of entries in each iqueue. */
#define IQUEUE_ENTRIES 512

/* Number of entries in each equeue. */
#define EQUEUE_ENTRIES 2048

/* Total header bytes per equeue slot.  Must be big enough for 2 bytes
 * of NET_IP_ALIGN alignment, plus 14 bytes (?) of L2 header, plus up to
 * 60 bytes of actual TCP header.  We round up to align to cache lines.
 */
#define HEADER_BYTES 128

/* Maximum completions per cpu per device (must be a power of two).
 * ISSUE: What is the right number here?  If this is too small, then
 * egress might block waiting for free space in a completions array.
 * ISSUE: At the least, allocate these only for initialized echannels.
 */
#define TILE_NET_MAX_COMPS 64

#define MAX_FRAGS (MAX_SKB_FRAGS + 1)

/* Size of completions data to allocate.
 * ISSUE: Probably more than needed since we don't use all the channels.
 */
#define COMPS_SIZE (TILE_NET_CHANNELS * sizeof(struct tile_net_comps))

/* Size of NotifRing data to allocate. */
#define NOTIF_RING_SIZE (IQUEUE_ENTRIES * sizeof(gxio_mpipe_idesc_t))

/* Timeout to wake the per-device TX timer after we stop the queue.
 * We don't want the timeout too short (adds overhead, and might end
 * up causing stop/wake/stop/wake cycles) or too long (affects performance).
 * For the 10 Gb NIC, 30 usec means roughly 30+ 1500-byte packets.
 */
#define TX_TIMER_DELAY_USEC 30

/* Timeout to wake the per-cpu egress timer to free completions. */
#define EGRESS_TIMER_DELAY_USEC 1000

MODULE_AUTHOR("Tilera Corporation");
MODULE_LICENSE("GPL");

/* A "packet fragment" (a chunk of memory). */
struct frag {
    void *buf;
    size_t length;
};

/* A single completion. */
struct tile_net_comp {
    /* The "complete_count" when the completion will be complete. */
    s64 when;
    /* The buffer to be freed when the completion is complete. */
    struct sk_buff *skb;
};

/* The completions for a given cpu and echannel. */
struct tile_net_comps {
    /* The completions. */
    struct tile_net_comp comp_queue[TILE_NET_MAX_COMPS];
    /* The number of completions used. */
    unsigned long comp_next;
    /* The number of completions freed. */
    unsigned long comp_last;
};

/* The transmit wake timer for a given cpu and echannel. */
struct tile_net_tx_wake {
    int tx_queue_idx;
    struct hrtimer timer;
    struct net_device *dev;
};

/* Info for a specific cpu. */
struct tile_net_info {
    /* The NAPI struct. */
    struct napi_struct napi;
    /* Packet queue. */
    gxio_mpipe_iqueue_t iqueue;
    /* Our cpu. */
    int my_cpu;
    /* True if iqueue is valid. */
    bool has_iqueue;
    /* NAPI flags. */
    bool napi_added;
    bool napi_enabled;
    /* Number of small sk_buffs which must still be provided. */
    unsigned int num_needed_small_buffers;
    /* Number of large sk_buffs which must still be provided. */
    unsigned int num_needed_large_buffers;
    /* A timer for handling egress completions. */
    struct hrtimer egress_timer;
    /* True if "egress_timer" is scheduled. */
    bool egress_timer_scheduled;
    /* Comps for each egress channel. */
    struct tile_net_comps *comps_for_echannel[TILE_NET_CHANNELS];
    /* Transmit wake timer for each egress channel. */
    struct tile_net_tx_wake tx_wake[TILE_NET_CHANNELS];
};

/* Info for egress on a particular egress channel. */
struct tile_net_egress {
    /* The "equeue". */
    gxio_mpipe_equeue_t *equeue;
    /* The headers for TSO. */
    unsigned char *headers;
};

/* Info for a specific device. */
struct tile_net_priv {
    /* Our network device. */
    struct net_device *dev;
    /* The primary link. */
    gxio_mpipe_link_t link;
    /* The primary channel, if open, else -1. */
    int channel;
    /* The "loopify" egress link, if needed. */
    gxio_mpipe_link_t loopify_link;
    /* The "loopify" egress channel, if open, else -1. */
    int loopify_channel;
    /* The egress channel (channel or loopify_channel). */
    int echannel;
    /* Total stats. */
    struct net_device_stats stats;
};

/* Egress info, indexed by "priv->echannel" (lazily created as needed). */
static struct tile_net_egress egress_for_echannel[TILE_NET_CHANNELS];

/* Devices currently associated with each channel.
 * NOTE: The array entry can become NULL after ifconfig down, but
 * we do not free the underlying net_device structures, so it is
 * safe to use a pointer after reading it from this array.
 */
static struct net_device *tile_net_devs_for_channel[TILE_NET_CHANNELS];

/* A mutex for "tile_net_devs_for_channel". */
static DEFINE_MUTEX(tile_net_devs_for_channel_mutex);

/* The per-cpu info. */
static DEFINE_PER_CPU(struct tile_net_info, per_cpu_info);

/* The "context" for all devices. */
static gxio_mpipe_context_t context;

/* Buffer sizes and mpipe enum codes for buffer stacks.
 * See arch/tile/include/gxio/mpipe.h for the set of possible values.
 */
#define BUFFER_SIZE_SMALL_ENUM GXIO_MPIPE_BUFFER_SIZE_128
#define BUFFER_SIZE_SMALL 128
#define BUFFER_SIZE_LARGE_ENUM GXIO_MPIPE_BUFFER_SIZE_1664
#define BUFFER_SIZE_LARGE 1664

/* The small/large "buffer stacks". */
static int small_buffer_stack = -1;
static int large_buffer_stack = -1;

/* Amount of memory allocated for each buffer stack. */
static size_t buffer_stack_size;

/* The actual memory allocated for the buffer stacks. */
static void *small_buffer_stack_va;
static void *large_buffer_stack_va;

/* The buckets. */
static int first_bucket = -1;
static int num_buckets = 1;

/* The ingress irq. */
static int ingress_irq = -1;

/* Text value of tile_net.cpus if passed as a module parameter. */
static char *network_cpus_string;

/* The actual cpus in "network_cpus". */
static struct cpumask network_cpus_map;

/* If "loopify=LINK" was specified, this is "LINK". */
static char *loopify_link_name;

/* If "tile_net.custom" was specified, this is non-NULL. */
static char *custom_str;

/* The "tile_net.cpus" argument specifies the cpus that are dedicated
 * to handle ingress packets.
 *
 * The parameter should be in the form "tile_net.cpus=m-n[,x-y]", where
 * m, n, x, y are integer numbers that represent the cpus that can be
 * neither a dedicated cpu nor a dataplane cpu.
 */
static bool network_cpus_init(void)
{
    char buf[1024];
    int rc;

    if (network_cpus_string == NULL)
        return false;

    rc = cpulist_parse_crop(network_cpus_string, &network_cpus_map);
    if (rc != 0) {
        pr_warn("tile_net.cpus=%s: malformed cpu list\n",
            network_cpus_string);
        return false;
    }

    /* Remove dedicated cpus. */
    cpumask_and(&network_cpus_map, &network_cpus_map, cpu_possible_mask);

    if (cpumask_empty(&network_cpus_map)) {
        pr_warn("Ignoring empty tile_net.cpus='%s'.\n",
            network_cpus_string);
        return false;
    }

    cpulist_scnprintf(buf, sizeof(buf), &network_cpus_map);
    pr_info("Linux network CPUs: %s\n", buf);
    return true;
}

module_param_named(cpus, network_cpus_string, charp, 0444);
MODULE_PARM_DESC(cpus, "cpulist of cores that handle network interrupts");

/* The "tile_net.loopify=LINK" argument causes the named device to
 * actually use "loop0" for ingress, and "loop1" for egress.  This
 * allows an app to sit between the actual link and linux, passing
 * (some) packets along to linux, and forwarding (some) packets sent
 * out by linux.
 */
module_param_named(loopify, loopify_link_name, charp, 0444);
MODULE_PARM_DESC(loopify, "name the device to use loop0/1 for ingress/egress");

/* The "tile_net.custom" argument causes us to ignore the "conventional"
 * classifier metadata, in particular, the "l2_offset".
 */
module_param_named(custom, custom_str, charp, 0444);
MODULE_PARM_DESC(custom, "indicates a (heavily) customized classifier");

/* Atomically update a statistics field.
 * Note that on TILE-Gx, this operation is fire-and-forget on the
 * issuing core (single-cycle dispatch) and takes only a few cycles
 * longer than a regular store when the request reaches the home cache.
 * No expensive bus management overhead is required.
 */
static void tile_net_stats_add(unsigned long value, unsigned long *field)
{
    BUILD_BUG_ON(sizeof(atomic_long_t) != sizeof(unsigned long));
    atomic_long_add(value, (atomic_long_t *)field);
}

/* Allocate and push a buffer. */
static bool tile_net_provide_buffer(bool small)
{
    int stack = small ? small_buffer_stack : large_buffer_stack;
    const unsigned long buffer_alignment = 128;
    struct sk_buff *skb;
    int len;

    len = sizeof(struct sk_buff **) + buffer_alignment;
    len += (small ? BUFFER_SIZE_SMALL : BUFFER_SIZE_LARGE);
    skb = dev_alloc_skb(len);
    if (skb == NULL)
        return false;

    /* Make room for a back-pointer to 'skb' and guarantee alignment. */
    skb_reserve(skb, sizeof(struct sk_buff **));
    skb_reserve(skb, -(long)skb->data & (buffer_alignment - 1));

    /* Save a back-pointer to 'skb'. */
    *(struct sk_buff **)(skb->data - sizeof(struct sk_buff **)) = skb;

    /* Make sure "skb" and the back-pointer have been flushed. */
    wmb();

    gxio_mpipe_push_buffer(&context, stack,
                   (void *)va_to_tile_io_addr(skb->data));

    return true;
}

/* Convert a raw mpipe buffer to its matching skb pointer. */
static struct sk_buff *mpipe_buf_to_skb(void *va)
{
    /* Acquire the associated "skb". */
    struct sk_buff **skb_ptr = va - sizeof(*skb_ptr);
    struct sk_buff *skb = *skb_ptr;

    /* Paranoia. */
    if (skb->data != va) {
        /* Panic here since there's a reasonable chance
         * that corrupt buffers means generic memory
         * corruption, with unpredictable system effects.
         */
        panic("Corrupt linux buffer! va=%p, skb=%p, skb->data=%p",
              va, skb, skb->data);
    }

    return skb;
}

static void tile_net_pop_all_buffers(int stack)
{
    for (;;) {
        tile_io_addr_t addr =
            (tile_io_addr_t)gxio_mpipe_pop_buffer(&context, stack);
        if (addr == 0)
            break;
        dev_kfree_skb_irq(mpipe_buf_to_skb(tile_io_addr_to_va(addr)));
    }
}

/* Provide linux buffers to mPIPE. */
static void tile_net_provide_needed_buffers(void)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);

    while (info->num_needed_small_buffers != 0) {
        if (!tile_net_provide_buffer(true))
            goto oops;
        info->num_needed_small_buffers--;
    }

    while (info->num_needed_large_buffers != 0) {
        if (!tile_net_provide_buffer(false))
            goto oops;
        info->num_needed_large_buffers--;
    }

    return;

oops:
    /* Add a description to the page allocation failure dump. */
    pr_notice("Tile %d still needs some buffers\n", info->my_cpu);
}

static inline bool filter_packet(struct net_device *dev, void *buf)
{
    /* Filter packets received before we're up. */
    if (dev == NULL || !(dev->flags & IFF_UP))
        return true;

    /* Filter out packets that aren't for us. */
    if (!(dev->flags & IFF_PROMISC) &&
        !is_multicast_ether_addr(buf) &&
        compare_ether_addr(dev->dev_addr, buf) != 0)
        return true;

    return false;
}

static void tile_net_receive_skb(struct net_device *dev, struct sk_buff *skb,
                 gxio_mpipe_idesc_t *idesc, unsigned long len)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    struct tile_net_priv *priv = netdev_priv(dev);

    /* Encode the actual packet length. */
    skb_put(skb, len);

    skb->protocol = eth_type_trans(skb, dev);

    /* Acknowledge "good" hardware checksums. */
    if (idesc->cs && idesc->csum_seed_val == 0xFFFF)
        skb->ip_summed = CHECKSUM_UNNECESSARY;

    netif_receive_skb(skb);

    /* Update stats. */
    tile_net_stats_add(1, &priv->stats.rx_packets);
    tile_net_stats_add(len, &priv->stats.rx_bytes);

    /* Need a new buffer. */
    if (idesc->size == BUFFER_SIZE_SMALL_ENUM)
        info->num_needed_small_buffers++;
    else
        info->num_needed_large_buffers++;
}

/* Handle a packet.  Return true if "processed", false if "filtered". */
static bool tile_net_handle_packet(gxio_mpipe_idesc_t *idesc)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    struct net_device *dev = tile_net_devs_for_channel[idesc->channel];
    uint8_t l2_offset;
    void *va;
    void *buf;
    unsigned long len;
    bool filter;

    /* Drop packets for which no buffer was available.
     * NOTE: This happens under heavy load.
     */
    if (idesc->be) {
        struct tile_net_priv *priv = netdev_priv(dev);
        tile_net_stats_add(1, &priv->stats.rx_dropped);
        gxio_mpipe_iqueue_consume(&info->iqueue, idesc);
        if (net_ratelimit())
            pr_info("Dropping packet (insufficient buffers).\n");
        return false;
    }

    /* Get the "l2_offset", if allowed. */
    l2_offset = custom_str ? 0 : gxio_mpipe_idesc_get_l2_offset(idesc);

    /* Get the raw buffer VA (includes "headroom"). */
    va = tile_io_addr_to_va((unsigned long)(long)idesc->va);

    /* Get the actual packet start/length. */
    buf = va + l2_offset;
    len = idesc->l2_size - l2_offset;

    /* Point "va" at the raw buffer. */
    va -= NET_IP_ALIGN;

    filter = filter_packet(dev, buf);
    if (filter) {
        gxio_mpipe_iqueue_drop(&info->iqueue, idesc);
    } else {
        struct sk_buff *skb = mpipe_buf_to_skb(va);

        /* Skip headroom, and any custom header. */
        skb_reserve(skb, NET_IP_ALIGN + l2_offset);

        tile_net_receive_skb(dev, skb, idesc, len);
    }

    gxio_mpipe_iqueue_consume(&info->iqueue, idesc);
    return !filter;
}

/* Handle some packets for the current CPU.
 *
 * This function handles up to TILE_NET_BATCH idescs per call.
 *
 * ISSUE: Since we do not provide new buffers until this function is
 * complete, we must initially provide enough buffers for each network
 * cpu to fill its iqueue and also its batched idescs.
 *
 * ISSUE: The "rotting packet" race condition occurs if a packet
 * arrives after the queue appears to be empty, and before the
 * hypervisor interrupt is re-enabled.
 */
static int tile_net_poll(struct napi_struct *napi, int budget)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    unsigned int work = 0;
    gxio_mpipe_idesc_t *idesc;
    int i, n;

    /* Process packets. */
    while ((n = gxio_mpipe_iqueue_try_peek(&info->iqueue, &idesc)) > 0) {
        for (i = 0; i < n; i++) {
            if (i == TILE_NET_BATCH)
                goto done;
            if (tile_net_handle_packet(idesc + i)) {
                if (++work >= budget)
                    goto done;
            }
        }
    }

    /* There are no packets left. */
    napi_complete(&info->napi);

    /* Re-enable hypervisor interrupts. */
    gxio_mpipe_enable_notif_ring_interrupt(&context, info->iqueue.ring);

    /* HACK: Avoid the "rotting packet" problem. */
    if (gxio_mpipe_iqueue_try_peek(&info->iqueue, &idesc) > 0)
        napi_schedule(&info->napi);

    /* ISSUE: Handle completions? */

done:
    tile_net_provide_needed_buffers();

    return work;
}

/* Handle an ingress interrupt on the current cpu. */
static irqreturn_t tile_net_handle_ingress_irq(int irq, void *unused)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    napi_schedule(&info->napi);
    return IRQ_HANDLED;
}

/* Free some completions.  This must be called with interrupts blocked. */
static int tile_net_free_comps(gxio_mpipe_equeue_t *equeue,
                struct tile_net_comps *comps,
                int limit, bool force_update)
{
    int n = 0;
    while (comps->comp_last < comps->comp_next) {
        unsigned int cid = comps->comp_last % TILE_NET_MAX_COMPS;
        struct tile_net_comp *comp = &comps->comp_queue[cid];
        if (!gxio_mpipe_equeue_is_complete(equeue, comp->when,
                           force_update || n == 0))
            break;
        dev_kfree_skb_irq(comp->skb);
        comps->comp_last++;
        if (++n == limit)
            break;
    }
    return n;
}

/* Add a completion.  This must be called with interrupts blocked.
 * tile_net_equeue_try_reserve() will have ensured a free completion entry.
 */
static void add_comp(gxio_mpipe_equeue_t *equeue,
             struct tile_net_comps *comps,
             uint64_t when, struct sk_buff *skb)
{
    int cid = comps->comp_next % TILE_NET_MAX_COMPS;
    comps->comp_queue[cid].when = when;
    comps->comp_queue[cid].skb = skb;
    comps->comp_next++;
}

static void tile_net_schedule_tx_wake_timer(struct net_device *dev,
                                            int tx_queue_idx)
{
    struct tile_net_info *info = &per_cpu(per_cpu_info, tx_queue_idx);
    struct tile_net_priv *priv = netdev_priv(dev);
    struct tile_net_tx_wake *tx_wake = &info->tx_wake[priv->echannel];

    hrtimer_start(&tx_wake->timer,
              ktime_set(0, TX_TIMER_DELAY_USEC * 1000UL),
              HRTIMER_MODE_REL_PINNED);
}

static enum hrtimer_restart tile_net_handle_tx_wake_timer(struct hrtimer *t)
{
    struct tile_net_tx_wake *tx_wake =
        container_of(t, struct tile_net_tx_wake, timer);
    netif_wake_subqueue(tx_wake->dev, tx_wake->tx_queue_idx);
    return HRTIMER_NORESTART;
}

/* Make sure the egress timer is scheduled. */
static void tile_net_schedule_egress_timer(void)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);

    if (!info->egress_timer_scheduled) {
        hrtimer_start(&info->egress_timer,
                  ktime_set(0, EGRESS_TIMER_DELAY_USEC * 1000UL),
                  HRTIMER_MODE_REL_PINNED);
        info->egress_timer_scheduled = true;
    }
}

/* The "function" for "info->egress_timer".
 *
 * This timer will reschedule itself as long as there are any pending
 * completions expected for this tile.
 */
static enum hrtimer_restart tile_net_handle_egress_timer(struct hrtimer *t)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    unsigned long irqflags;
    bool pending = false;
    int i;

    local_irq_save(irqflags);

    /* The timer is no longer scheduled. */
    info->egress_timer_scheduled = false;

    /* Free all possible comps for this tile. */
    for (i = 0; i < TILE_NET_CHANNELS; i++) {
        struct tile_net_egress *egress = &egress_for_echannel[i];
        struct tile_net_comps *comps = info->comps_for_echannel[i];
        if (comps->comp_last >= comps->comp_next)
            continue;
        tile_net_free_comps(egress->equeue, comps, -1, true);
        pending = pending || (comps->comp_last < comps->comp_next);
    }

    /* Reschedule timer if needed. */
    if (pending)
        tile_net_schedule_egress_timer();

    local_irq_restore(irqflags);

    return HRTIMER_NORESTART;
}

/* Helper function for "tile_net_update()".
 * "dev" (i.e. arg) is the device being brought up or down,
 * or NULL if all devices are now down.
 */
static void tile_net_update_cpu(void *arg)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    struct net_device *dev = arg;

    if (!info->has_iqueue)
        return;

    if (dev != NULL) {
        if (!info->napi_added) {
            netif_napi_add(dev, &info->napi,
                       tile_net_poll, TILE_NET_WEIGHT);
            info->napi_added = true;
        }
        if (!info->napi_enabled) {
            napi_enable(&info->napi);
            info->napi_enabled = true;
        }
        enable_percpu_irq(ingress_irq, 0);
    } else {
        disable_percpu_irq(ingress_irq);
        if (info->napi_enabled) {
            napi_disable(&info->napi);
            info->napi_enabled = false;
        }
        /* FIXME: Drain the iqueue. */
    }
}

/* Helper function for tile_net_open() and tile_net_stop().
 * Always called under tile_net_devs_for_channel_mutex.
 */
static int tile_net_update(struct net_device *dev)
{
    static gxio_mpipe_rules_t rules;  /* too big to fit on the stack */
    bool saw_channel = false;
    int channel;
    int rc;
    int cpu;

    gxio_mpipe_rules_init(&rules, &context);

    for (channel = 0; channel < TILE_NET_CHANNELS; channel++) {
        if (tile_net_devs_for_channel[channel] == NULL)
            continue;
        if (!saw_channel) {
            saw_channel = true;
            gxio_mpipe_rules_begin(&rules, first_bucket,
                           num_buckets, NULL);
            gxio_mpipe_rules_set_headroom(&rules, NET_IP_ALIGN);
        }
        gxio_mpipe_rules_add_channel(&rules, channel);
    }

    /* NOTE: This can fail if there is no classifier.
     * ISSUE: Can anything else cause it to fail?
     */
    rc = gxio_mpipe_rules_commit(&rules);
    if (rc != 0) {
        netdev_warn(dev, "gxio_mpipe_rules_commit failed: %d\n", rc);
        return -EIO;
    }

    /* Update all cpus, sequentially (to protect "netif_napi_add()"). */
    for_each_online_cpu(cpu)
        smp_call_function_single(cpu, tile_net_update_cpu,
                     (saw_channel ? dev : NULL), 1);

    /* HACK: Allow packets to flow in the simulator. */
    if (saw_channel)
        sim_enable_mpipe_links(0, -1);

    return 0;
}

/* Allocate and initialize mpipe buffer stacks, and register them in
 * the mPIPE TLBs, for both small and large packet sizes.
 * This routine supports tile_net_init_mpipe(), below.
 */
static int init_buffer_stacks(struct net_device *dev, int num_buffers)
{
    pte_t hash_pte = pte_set_home((pte_t) { 0 }, PAGE_HOME_HASH);
    int rc;

    /* Compute stack bytes; we round up to 64KB and then use
     * alloc_pages() so we get the required 64KB alignment as well.
     */
    buffer_stack_size =
        ALIGN(gxio_mpipe_calc_buffer_stack_bytes(num_buffers),
              64 * 1024);

    /* Allocate two buffer stack indices. */
    rc = gxio_mpipe_alloc_buffer_stacks(&context, 2, 0, 0);
    if (rc < 0) {
        netdev_err(dev, "gxio_mpipe_alloc_buffer_stacks failed: %d\n",
               rc);
        return rc;
    }
    small_buffer_stack = rc;
    large_buffer_stack = rc + 1;

    /* Allocate the small memory stack. */
    small_buffer_stack_va =
        alloc_pages_exact(buffer_stack_size, GFP_KERNEL);
    if (small_buffer_stack_va == NULL) {
        netdev_err(dev,
               "Could not alloc %zd bytes for buffer stacks\n",
               buffer_stack_size);
        return -ENOMEM;
    }
    rc = gxio_mpipe_init_buffer_stack(&context, small_buffer_stack,
                      BUFFER_SIZE_SMALL_ENUM,
                      small_buffer_stack_va,
                      buffer_stack_size, 0);
    if (rc != 0) {
        netdev_err(dev, "gxio_mpipe_init_buffer_stack: %d\n", rc);
        return rc;
    }
    rc = gxio_mpipe_register_client_memory(&context, small_buffer_stack,
                           hash_pte, 0);
    if (rc != 0) {
        netdev_err(dev,
               "gxio_mpipe_register_buffer_memory failed: %d\n",
               rc);
        return rc;
    }

    /* Allocate the large buffer stack. */
    large_buffer_stack_va =
        alloc_pages_exact(buffer_stack_size, GFP_KERNEL);
    if (large_buffer_stack_va == NULL) {
        netdev_err(dev,
               "Could not alloc %zd bytes for buffer stacks\n",
               buffer_stack_size);
        return -ENOMEM;
    }
    rc = gxio_mpipe_init_buffer_stack(&context, large_buffer_stack,
                      BUFFER_SIZE_LARGE_ENUM,
                      large_buffer_stack_va,
                      buffer_stack_size, 0);
    if (rc != 0) {
        netdev_err(dev, "gxio_mpipe_init_buffer_stack failed: %d\n",
               rc);
        return rc;
    }
    rc = gxio_mpipe_register_client_memory(&context, large_buffer_stack,
                           hash_pte, 0);
    if (rc != 0) {
        netdev_err(dev,
               "gxio_mpipe_register_buffer_memory failed: %d\n",
               rc);
        return rc;
    }

    return 0;
}

/* Allocate per-cpu resources (memory for completions and idescs).
 * This routine supports tile_net_init_mpipe(), below.
 */
static int alloc_percpu_mpipe_resources(struct net_device *dev,
                    int cpu, int ring)
{
    struct tile_net_info *info = &per_cpu(per_cpu_info, cpu);
    int order, i, rc;
    struct page *page;
    void *addr;

    /* Allocate the "comps". */
    order = get_order(COMPS_SIZE);
    page = homecache_alloc_pages(GFP_KERNEL, order, cpu);
    if (page == NULL) {
        netdev_err(dev, "Failed to alloc %zd bytes comps memory\n",
               COMPS_SIZE);
        return -ENOMEM;
    }
    addr = pfn_to_kaddr(page_to_pfn(page));
    memset(addr, 0, COMPS_SIZE);
    for (i = 0; i < TILE_NET_CHANNELS; i++)
        info->comps_for_echannel[i] =
            addr + i * sizeof(struct tile_net_comps);

    /* If this is a network cpu, create an iqueue. */
    if (cpu_isset(cpu, network_cpus_map)) {
        order = get_order(NOTIF_RING_SIZE);
        page = homecache_alloc_pages(GFP_KERNEL, order, cpu);
        if (page == NULL) {
            netdev_err(dev,
                   "Failed to alloc %zd bytes iqueue memory\n",
                   NOTIF_RING_SIZE);
            return -ENOMEM;
        }
        addr = pfn_to_kaddr(page_to_pfn(page));
        rc = gxio_mpipe_iqueue_init(&info->iqueue, &context, ring++,
                        addr, NOTIF_RING_SIZE, 0);
        if (rc < 0) {
            netdev_err(dev,
                   "gxio_mpipe_iqueue_init failed: %d\n", rc);
            return rc;
        }
        info->has_iqueue = true;
    }

    return ring;
}

/* Initialize NotifGroup and buckets.
 * This routine supports tile_net_init_mpipe(), below.
 */
static int init_notif_group_and_buckets(struct net_device *dev,
                    int ring, int network_cpus_count)
{
    int group, rc;

    /* Allocate one NotifGroup. */
    rc = gxio_mpipe_alloc_notif_groups(&context, 1, 0, 0);
    if (rc < 0) {
        netdev_err(dev, "gxio_mpipe_alloc_notif_groups failed: %d\n",
               rc);
        return rc;
    }
    group = rc;

    /* Initialize global num_buckets value. */
    if (network_cpus_count > 4)
        num_buckets = 256;
    else if (network_cpus_count > 1)
        num_buckets = 16;

    /* Allocate some buckets, and set global first_bucket value. */
    rc = gxio_mpipe_alloc_buckets(&context, num_buckets, 0, 0);
    if (rc < 0) {
        netdev_err(dev, "gxio_mpipe_alloc_buckets failed: %d\n", rc);
        return rc;
    }
    first_bucket = rc;

    /* Init group and buckets. */
    rc = gxio_mpipe_init_notif_group_and_buckets(
        &context, group, ring, network_cpus_count,
        first_bucket, num_buckets,
        GXIO_MPIPE_BUCKET_STICKY_FLOW_LOCALITY);
    if (rc != 0) {
        netdev_err(
            dev,
            "gxio_mpipe_init_notif_group_and_buckets failed: %d\n",
            rc);
        return rc;
    }

    return 0;
}

/* Create an irq and register it, then activate the irq and request
 * interrupts on all cores.  Note that "ingress_irq" being initialized
 * is how we know not to call tile_net_init_mpipe() again.
 * This routine supports tile_net_init_mpipe(), below.
 */
static int tile_net_setup_interrupts(struct net_device *dev)
{
    int cpu, rc;

    rc = create_irq();
    if (rc < 0) {
        netdev_err(dev, "create_irq failed: %d\n", rc);
        return rc;
    }
    ingress_irq = rc;
    tile_irq_activate(ingress_irq, TILE_IRQ_PERCPU);
    rc = request_irq(ingress_irq, tile_net_handle_ingress_irq,
             0, "tile_net", NULL);
    if (rc != 0) {
        netdev_err(dev, "request_irq failed: %d\n", rc);
        destroy_irq(ingress_irq);
        ingress_irq = -1;
        return rc;
    }

    for_each_online_cpu(cpu) {
        struct tile_net_info *info = &per_cpu(per_cpu_info, cpu);
        if (info->has_iqueue) {
            gxio_mpipe_request_notif_ring_interrupt(
                &context, cpu_x(cpu), cpu_y(cpu),
                1, ingress_irq, info->iqueue.ring);
        }
    }

    return 0;
}

/* Undo any state set up partially by a failed call to tile_net_init_mpipe. */
static void tile_net_init_mpipe_fail(void)
{
    int cpu;

    /* Do cleanups that require the mpipe context first. */
    if (small_buffer_stack >= 0)
        tile_net_pop_all_buffers(small_buffer_stack);
    if (large_buffer_stack >= 0)
        tile_net_pop_all_buffers(large_buffer_stack);

    /* Destroy mpipe context so the hardware no longer owns any memory. */
    gxio_mpipe_destroy(&context);

    for_each_online_cpu(cpu) {
        struct tile_net_info *info = &per_cpu(per_cpu_info, cpu);
        free_pages((unsigned long)(info->comps_for_echannel[0]),
               get_order(COMPS_SIZE));
        info->comps_for_echannel[0] = NULL;
        free_pages((unsigned long)(info->iqueue.idescs),
               get_order(NOTIF_RING_SIZE));
        info->iqueue.idescs = NULL;
    }

    if (small_buffer_stack_va)
        free_pages_exact(small_buffer_stack_va, buffer_stack_size);
    if (large_buffer_stack_va)
        free_pages_exact(large_buffer_stack_va, buffer_stack_size);

    small_buffer_stack_va = NULL;
    large_buffer_stack_va = NULL;
    large_buffer_stack = -1;
    small_buffer_stack = -1;
    first_bucket = -1;
}

/* The first time any tilegx network device is opened, we initialize
 * the global mpipe state.  If this step fails, we fail to open the
 * device, but if it succeeds, we never need to do it again, and since
 * tile_net can't be unloaded, we never undo it.
 *
 * Note that some resources in this path (buffer stack indices,
 * bindings from init_buffer_stack, etc.) are hypervisor resources
 * that are freed implicitly by gxio_mpipe_destroy().
 */
static int tile_net_init_mpipe(struct net_device *dev)
{
    int i, num_buffers, rc;
    int cpu;
    int first_ring, ring;
    int network_cpus_count = cpus_weight(network_cpus_map);

    if (!hash_default) {
        netdev_err(dev, "Networking requires hash_default!\n");
        return -EIO;
    }

    rc = gxio_mpipe_init(&context, 0);
    if (rc != 0) {
        netdev_err(dev, "gxio_mpipe_init failed: %d\n", rc);
        return -EIO;
    }

    /* Set up the buffer stacks. */
    num_buffers =
        network_cpus_count * (IQUEUE_ENTRIES + TILE_NET_BATCH);
    rc = init_buffer_stacks(dev, num_buffers);
    if (rc != 0)
        goto fail;

    /* Provide initial buffers. */
    rc = -ENOMEM;
    for (i = 0; i < num_buffers; i++) {
        if (!tile_net_provide_buffer(true)) {
            netdev_err(dev, "Cannot allocate initial sk_bufs!\n");
            goto fail;
        }
    }
    for (i = 0; i < num_buffers; i++) {
        if (!tile_net_provide_buffer(false)) {
            netdev_err(dev, "Cannot allocate initial sk_bufs!\n");
            goto fail;
        }
    }

    /* Allocate one NotifRing for each network cpu. */
    rc = gxio_mpipe_alloc_notif_rings(&context, network_cpus_count, 0, 0);
    if (rc < 0) {
        netdev_err(dev, "gxio_mpipe_alloc_notif_rings failed %d\n",
               rc);
        goto fail;
    }

    /* Init NotifRings per-cpu. */
    first_ring = rc;
    ring = first_ring;
    for_each_online_cpu(cpu) {
        rc = alloc_percpu_mpipe_resources(dev, cpu, ring);
        if (rc < 0)
            goto fail;
        ring = rc;
    }

    /* Initialize NotifGroup and buckets. */
    rc = init_notif_group_and_buckets(dev, first_ring, network_cpus_count);
    if (rc != 0)
        goto fail;

    /* Create and enable interrupts. */
    rc = tile_net_setup_interrupts(dev);
    if (rc != 0)
        goto fail;

    return 0;

fail:
    tile_net_init_mpipe_fail();
    return rc;
}

/* Create persistent egress info for a given egress channel.
 * Note that this may be shared between, say, "gbe0" and "xgbe0".
 * ISSUE: Defer header allocation until TSO is actually needed?
 */
static int tile_net_init_egress(struct net_device *dev, int echannel)
{
    struct page *headers_page, *edescs_page, *equeue_page;
    gxio_mpipe_edesc_t *edescs;
    gxio_mpipe_equeue_t *equeue;
    unsigned char *headers;
    int headers_order, edescs_order, equeue_order;
    size_t edescs_size;
    int edma;
    int rc = -ENOMEM;

    /* Only initialize once. */
    if (egress_for_echannel[echannel].equeue != NULL)
        return 0;

    /* Allocate memory for the "headers". */
    headers_order = get_order(EQUEUE_ENTRIES * HEADER_BYTES);
    headers_page = alloc_pages(GFP_KERNEL, headers_order);
    if (headers_page == NULL) {
        netdev_warn(dev,
                "Could not alloc %zd bytes for TSO headers.\n",
                PAGE_SIZE << headers_order);
        goto fail;
    }
    headers = pfn_to_kaddr(page_to_pfn(headers_page));

    /* Allocate memory for the "edescs". */
    edescs_size = EQUEUE_ENTRIES * sizeof(*edescs);
    edescs_order = get_order(edescs_size);
    edescs_page = alloc_pages(GFP_KERNEL, edescs_order);
    if (edescs_page == NULL) {
        netdev_warn(dev,
                "Could not alloc %zd bytes for eDMA ring.\n",
                edescs_size);
        goto fail_headers;
    }
    edescs = pfn_to_kaddr(page_to_pfn(edescs_page));

    /* Allocate memory for the "equeue". */
    equeue_order = get_order(sizeof(*equeue));
    equeue_page = alloc_pages(GFP_KERNEL, equeue_order);
    if (equeue_page == NULL) {
        netdev_warn(dev,
                "Could not alloc %zd bytes for equeue info.\n",
                PAGE_SIZE << equeue_order);
        goto fail_edescs;
    }
    equeue = pfn_to_kaddr(page_to_pfn(equeue_page));

    /* Allocate an edma ring.  Note that in practice this can't
     * fail, which is good, because we will leak an edma ring if so.
     */
    rc = gxio_mpipe_alloc_edma_rings(&context, 1, 0, 0);
    if (rc < 0) {
        netdev_warn(dev, "gxio_mpipe_alloc_edma_rings failed: %d\n",
                rc);
        goto fail_equeue;
    }
    edma = rc;

    /* Initialize the equeue. */
    rc = gxio_mpipe_equeue_init(equeue, &context, edma, echannel,
                    edescs, edescs_size, 0);
    if (rc != 0) {
        netdev_err(dev, "gxio_mpipe_equeue_init failed: %d\n", rc);
        goto fail_equeue;
    }

    /* Done. */
    egress_for_echannel[echannel].equeue = equeue;
    egress_for_echannel[echannel].headers = headers;
    return 0;

fail_equeue:
    __free_pages(equeue_page, equeue_order);

fail_edescs:
    __free_pages(edescs_page, edescs_order);

fail_headers:
    __free_pages(headers_page, headers_order);

fail:
    return rc;
}

/* Return channel number for a newly-opened link. */
static int tile_net_link_open(struct net_device *dev, gxio_mpipe_link_t *link,
                  const char *link_name)
{
    int rc = gxio_mpipe_link_open(link, &context, link_name, 0);
    if (rc < 0) {
        netdev_err(dev, "Failed to open '%s'\n", link_name);
        return rc;
    }
    rc = gxio_mpipe_link_channel(link);
    if (rc < 0 || rc >= TILE_NET_CHANNELS) {
        netdev_err(dev, "gxio_mpipe_link_channel bad value: %d\n", rc);
        gxio_mpipe_link_close(link);
        return -EINVAL;
    }
    return rc;
}

/* Help the kernel activate the given network interface. */
static int tile_net_open(struct net_device *dev)
{
    struct tile_net_priv *priv = netdev_priv(dev);
    int cpu, rc;

    mutex_lock(&tile_net_devs_for_channel_mutex);

    /* Do one-time initialization the first time any device is opened. */
    if (ingress_irq < 0) {
        rc = tile_net_init_mpipe(dev);
        if (rc != 0)
            goto fail;
    }

    /* Determine if this is the "loopify" device. */
    if (unlikely((loopify_link_name != NULL) &&
             !strcmp(dev->name, loopify_link_name))) {
        rc = tile_net_link_open(dev, &priv->link, "loop0");
        if (rc < 0)
            goto fail;
        priv->channel = rc;
        rc = tile_net_link_open(dev, &priv->loopify_link, "loop1");
        if (rc < 0)
            goto fail;
        priv->loopify_channel = rc;
        priv->echannel = rc;
    } else {
        rc = tile_net_link_open(dev, &priv->link, dev->name);
        if (rc < 0)
            goto fail;
        priv->channel = rc;
        priv->echannel = rc;
    }

    /* Initialize egress info (if needed).  Once ever, per echannel. */
    rc = tile_net_init_egress(dev, priv->echannel);
    if (rc != 0)
        goto fail;

    tile_net_devs_for_channel[priv->channel] = dev;

    rc = tile_net_update(dev);
    if (rc != 0)
        goto fail;

    mutex_unlock(&tile_net_devs_for_channel_mutex);

    /* Initialize the transmit wake timer for this device for each cpu. */
    for_each_online_cpu(cpu) {
        struct tile_net_info *info = &per_cpu(per_cpu_info, cpu);
        struct tile_net_tx_wake *tx_wake =
            &info->tx_wake[priv->echannel];

        hrtimer_init(&tx_wake->timer, CLOCK_MONOTONIC,
                 HRTIMER_MODE_REL);
        tx_wake->tx_queue_idx = cpu;
        tx_wake->timer.function = tile_net_handle_tx_wake_timer;
        tx_wake->dev = dev;
    }

    for_each_online_cpu(cpu)
        netif_start_subqueue(dev, cpu);
    netif_carrier_on(dev);
    return 0;

fail:
    if (priv->loopify_channel >= 0) {
        if (gxio_mpipe_link_close(&priv->loopify_link) != 0)
            netdev_warn(dev, "Failed to close loopify link!\n");
        priv->loopify_channel = -1;
    }
    if (priv->channel >= 0) {
        if (gxio_mpipe_link_close(&priv->link) != 0)
            netdev_warn(dev, "Failed to close link!\n");
        priv->channel = -1;
    }
    priv->echannel = -1;
    tile_net_devs_for_channel[priv->channel] = NULL;
    mutex_unlock(&tile_net_devs_for_channel_mutex);

    /* Don't return raw gxio error codes to generic Linux. */
    return (rc > -512) ? rc : -EIO;
}

/* Help the kernel deactivate the given network interface. */
static int tile_net_stop(struct net_device *dev)
{
    struct tile_net_priv *priv = netdev_priv(dev);
    int cpu;

    for_each_online_cpu(cpu) {
        struct tile_net_info *info = &per_cpu(per_cpu_info, cpu);
        struct tile_net_tx_wake *tx_wake =
            &info->tx_wake[priv->echannel];

        hrtimer_cancel(&tx_wake->timer);
        netif_stop_subqueue(dev, cpu);
    }

    mutex_lock(&tile_net_devs_for_channel_mutex);
    tile_net_devs_for_channel[priv->channel] = NULL;
    (void)tile_net_update(dev);
    if (priv->loopify_channel >= 0) {
        if (gxio_mpipe_link_close(&priv->loopify_link) != 0)
            netdev_warn(dev, "Failed to close loopify link!\n");
        priv->loopify_channel = -1;
    }
    if (priv->channel >= 0) {
        if (gxio_mpipe_link_close(&priv->link) != 0)
            netdev_warn(dev, "Failed to close link!\n");
        priv->channel = -1;
    }
    priv->echannel = -1;
    mutex_unlock(&tile_net_devs_for_channel_mutex);

    return 0;
}

/* Determine the VA for a fragment. */
static inline void *tile_net_frag_buf(skb_frag_t *f)
{
    unsigned long pfn = page_to_pfn(skb_frag_page(f));
    return pfn_to_kaddr(pfn) + f->page_offset;
}

/* Acquire a completion entry and an egress slot, or if we can't,
 * stop the queue and schedule the tx_wake timer.
 */
static s64 tile_net_equeue_try_reserve(struct net_device *dev,
                       int tx_queue_idx,
                       struct tile_net_comps *comps,
                       gxio_mpipe_equeue_t *equeue,
                       int num_edescs)
{
    /* Try to acquire a completion entry. */
    if (comps->comp_next - comps->comp_last < TILE_NET_MAX_COMPS - 1 ||
        tile_net_free_comps(equeue, comps, 32, false) != 0) {

        /* Try to acquire an egress slot. */
        s64 slot = gxio_mpipe_equeue_try_reserve(equeue, num_edescs);
        if (slot >= 0)
            return slot;

        /* Freeing some completions gives the equeue time to drain. */
        tile_net_free_comps(equeue, comps, TILE_NET_MAX_COMPS, false);

        slot = gxio_mpipe_equeue_try_reserve(equeue, num_edescs);
        if (slot >= 0)
            return slot;
    }

    /* Still nothing; give up and stop the queue for a short while. */
    netif_stop_subqueue(dev, tx_queue_idx);
    tile_net_schedule_tx_wake_timer(dev, tx_queue_idx);
    return -1;
}

/* Determine how many edesc's are needed for TSO.
 *
 * Sometimes, if "sendfile()" requires copying, we will be called with
 * "data" containing the header and payload, with "frags" being empty.
 * Sometimes, for example when using NFS over TCP, a single segment can
 * span 3 fragments.  This requires special care.
 */
static int tso_count_edescs(struct sk_buff *skb)
{
    struct skb_shared_info *sh = skb_shinfo(skb);
    unsigned int sh_len = skb_transport_offset(skb) + tcp_hdrlen(skb);
    unsigned int data_len = skb->len - sh_len;
    unsigned int p_len = sh->gso_size;
    long f_id = -1;    /* id of the current fragment */
    long f_size = skb_headlen(skb) - sh_len;  /* current fragment size */
    long f_used = 0;  /* bytes used from the current fragment */
    long n;            /* size of the current piece of payload */
    int num_edescs = 0;
    int segment;

    for (segment = 0; segment < sh->gso_segs; segment++) {

        unsigned int p_used = 0;

        /* One edesc for header and for each piece of the payload. */
        for (num_edescs++; p_used < p_len; num_edescs++) {

            /* Advance as needed. */
            while (f_used >= f_size) {
                f_id++;
                f_size = skb_frag_size(&sh->frags[f_id]);
                f_used = 0;
            }

            /* Use bytes from the current fragment. */
            n = p_len - p_used;
            if (n > f_size - f_used)
                n = f_size - f_used;
            f_used += n;
            p_used += n;
        }

        /* The last segment may be less than gso_size. */
        data_len -= p_len;
        if (data_len < p_len)
            p_len = data_len;
    }

    return num_edescs;
}

/* Prepare modified copies of the skbuff headers.
 * FIXME: add support for IPv6.
 */
static void tso_headers_prepare(struct sk_buff *skb, unsigned char *headers,
                s64 slot)
{
    struct skb_shared_info *sh = skb_shinfo(skb);
    struct iphdr *ih;
    struct tcphdr *th;
    unsigned int sh_len = skb_transport_offset(skb) + tcp_hdrlen(skb);
    unsigned int data_len = skb->len - sh_len;
    unsigned char *data = skb->data;
    unsigned int ih_off, th_off, p_len;
    unsigned int isum_seed, tsum_seed, id, seq;
    long f_id = -1;    /* id of the current fragment */
    long f_size = skb_headlen(skb) - sh_len;  /* current fragment size */
    long f_used = 0;  /* bytes used from the current fragment */
    long n;            /* size of the current piece of payload */
    int segment;

    /* Locate original headers and compute various lengths. */
    ih = ip_hdr(skb);
    th = tcp_hdr(skb);
    ih_off = skb_network_offset(skb);
    th_off = skb_transport_offset(skb);
    p_len = sh->gso_size;

    /* Set up seed values for IP and TCP csum and initialize id and seq. */
    isum_seed = ((0xFFFF - ih->check) +
             (0xFFFF - ih->tot_len) +
             (0xFFFF - ih->id));
    tsum_seed = th->check + (0xFFFF ^ htons(skb->len));
    id = ntohs(ih->id);
    seq = ntohl(th->seq);

    /* Prepare all the headers. */
    for (segment = 0; segment < sh->gso_segs; segment++) {
        unsigned char *buf;
        unsigned int p_used = 0;

        /* Copy to the header memory for this segment. */
        buf = headers + (slot % EQUEUE_ENTRIES) * HEADER_BYTES +
            NET_IP_ALIGN;
        memcpy(buf, data, sh_len);

        /* Update copied ip header. */
        ih = (struct iphdr *)(buf + ih_off);
        ih->tot_len = htons(sh_len + p_len - ih_off);
        ih->id = htons(id);
        ih->check = csum_long(isum_seed + ih->tot_len +
                      ih->id) ^ 0xffff;

        /* Update copied tcp header. */
        th = (struct tcphdr *)(buf + th_off);
        th->seq = htonl(seq);
        th->check = csum_long(tsum_seed + htons(sh_len + p_len));
        if (segment != sh->gso_segs - 1) {
            th->fin = 0;
            th->psh = 0;
        }

        /* Skip past the header. */
        slot++;

        /* Skip past the payload. */
        while (p_used < p_len) {

            /* Advance as needed. */
            while (f_used >= f_size) {
                f_id++;
                f_size = skb_frag_size(&sh->frags[f_id]);
                f_used = 0;
            }

            /* Use bytes from the current fragment. */
            n = p_len - p_used;
            if (n > f_size - f_used)
                n = f_size - f_used;
            f_used += n;
            p_used += n;

            slot++;
        }

        id++;
        seq += p_len;

        /* The last segment may be less than gso_size. */
        data_len -= p_len;
        if (data_len < p_len)
            p_len = data_len;
    }

    /* Flush the headers so they are ready for hardware DMA. */
    wmb();
}

/* Pass all the data to mpipe for egress. */
static void tso_egress(struct net_device *dev, gxio_mpipe_equeue_t *equeue,
               struct sk_buff *skb, unsigned char *headers, s64 slot)
{
    struct tile_net_priv *priv = netdev_priv(dev);
    struct skb_shared_info *sh = skb_shinfo(skb);
    unsigned int sh_len = skb_transport_offset(skb) + tcp_hdrlen(skb);
    unsigned int data_len = skb->len - sh_len;
    unsigned int p_len = sh->gso_size;
    gxio_mpipe_edesc_t edesc_head = { { 0 } };
    gxio_mpipe_edesc_t edesc_body = { { 0 } };
    long f_id = -1;    /* id of the current fragment */
    long f_size = skb_headlen(skb) - sh_len;  /* current fragment size */
    long f_used = 0;  /* bytes used from the current fragment */
    void *f_data = skb->data + sh_len;
    long n;            /* size of the current piece of payload */
    unsigned long tx_packets = 0, tx_bytes = 0;
    unsigned int csum_start;
    int segment;

    /* Prepare to egress the headers: set up header edesc. */
    csum_start = skb_checksum_start_offset(skb);
    edesc_head.csum = 1;
    edesc_head.csum_start = csum_start;
    edesc_head.csum_dest = csum_start + skb->csum_offset;
    edesc_head.xfer_size = sh_len;

    /* This is only used to specify the TLB. */
    edesc_head.stack_idx = large_buffer_stack;
    edesc_body.stack_idx = large_buffer_stack;

    /* Egress all the edescs. */
    for (segment = 0; segment < sh->gso_segs; segment++) {
        unsigned char *buf;
        unsigned int p_used = 0;

        /* Egress the header. */
        buf = headers + (slot % EQUEUE_ENTRIES) * HEADER_BYTES +
            NET_IP_ALIGN;
        edesc_head.va = va_to_tile_io_addr(buf);
        gxio_mpipe_equeue_put_at(equeue, edesc_head, slot);
        slot++;

        /* Egress the payload. */
        while (p_used < p_len) {
            void *va;

            /* Advance as needed. */
            while (f_used >= f_size) {
                f_id++;
                f_size = skb_frag_size(&sh->frags[f_id]);
                f_data = tile_net_frag_buf(&sh->frags[f_id]);
                f_used = 0;
            }

            va = f_data + f_used;

            /* Use bytes from the current fragment. */
            n = p_len - p_used;
            if (n > f_size - f_used)
                n = f_size - f_used;
            f_used += n;
            p_used += n;

            /* Egress a piece of the payload. */
            edesc_body.va = va_to_tile_io_addr(va);
            edesc_body.xfer_size = n;
            edesc_body.bound = !(p_used < p_len);
            gxio_mpipe_equeue_put_at(equeue, edesc_body, slot);
            slot++;
        }

        tx_packets++;
        tx_bytes += sh_len + p_len;

        /* The last segment may be less than gso_size. */
        data_len -= p_len;
        if (data_len < p_len)
            p_len = data_len;
    }

    /* Update stats. */
    tile_net_stats_add(tx_packets, &priv->stats.tx_packets);
    tile_net_stats_add(tx_bytes, &priv->stats.tx_bytes);
}

/* Do "TSO" handling for egress.
 *
 * Normally drivers set NETIF_F_TSO only to support hardware TSO;
 * otherwise the stack uses scatter-gather to implement GSO in software.
 * On our testing, enabling GSO support (via NETIF_F_SG) drops network
 * performance down to around 7.5 Gbps on the 10G interfaces, although
 * also dropping cpu utilization way down, to under 8%.  But
 * implementing "TSO" in the driver brings performance back up to line
 * rate, while dropping cpu usage even further, to less than 4%.  In
 * practice, profiling of GSO shows that skb_segment() is what causes
 * the performance overheads; we benefit in the driver from using
 * preallocated memory to duplicate the TCP/IP headers.
 */
static int tile_net_tx_tso(struct sk_buff *skb, struct net_device *dev)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    struct tile_net_priv *priv = netdev_priv(dev);
    int channel = priv->echannel;
    struct tile_net_egress *egress = &egress_for_echannel[channel];
    struct tile_net_comps *comps = info->comps_for_echannel[channel];
    gxio_mpipe_equeue_t *equeue = egress->equeue;
    unsigned long irqflags;
    int num_edescs;
    s64 slot;

    /* Determine how many mpipe edesc's are needed. */
    num_edescs = tso_count_edescs(skb);

    local_irq_save(irqflags);

    /* Try to acquire a completion entry and an egress slot. */
    slot = tile_net_equeue_try_reserve(dev, skb->queue_mapping, comps,
                       equeue, num_edescs);
    if (slot < 0) {
        local_irq_restore(irqflags);
        return NETDEV_TX_BUSY;
    }

    /* Set up copies of header data properly. */
    tso_headers_prepare(skb, egress->headers, slot);

    /* Actually pass the data to the network hardware. */
    tso_egress(dev, equeue, skb, egress->headers, slot);

    /* Add a completion record. */
    add_comp(equeue, comps, slot + num_edescs - 1, skb);

    local_irq_restore(irqflags);

    /* Make sure the egress timer is scheduled. */
    tile_net_schedule_egress_timer();

    return NETDEV_TX_OK;
}

/* Analyze the body and frags for a transmit request. */
static unsigned int tile_net_tx_frags(struct frag *frags,
                       struct sk_buff *skb,
                       void *b_data, unsigned int b_len)
{
    unsigned int i, n = 0;

    struct skb_shared_info *sh = skb_shinfo(skb);

    if (b_len != 0) {
        frags[n].buf = b_data;
        frags[n++].length = b_len;
    }

    for (i = 0; i < sh->nr_frags; i++) {
        skb_frag_t *f = &sh->frags[i];
        frags[n].buf = tile_net_frag_buf(f);
        frags[n++].length = skb_frag_size(f);
    }

    return n;
}

/* Help the kernel transmit a packet. */
static int tile_net_tx(struct sk_buff *skb, struct net_device *dev)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    struct tile_net_priv *priv = netdev_priv(dev);
    struct tile_net_egress *egress = &egress_for_echannel[priv->echannel];
    gxio_mpipe_equeue_t *equeue = egress->equeue;
    struct tile_net_comps *comps =
        info->comps_for_echannel[priv->echannel];
    unsigned int len = skb->len;
    unsigned char *data = skb->data;
    unsigned int num_edescs;
    struct frag frags[MAX_FRAGS];
    gxio_mpipe_edesc_t edescs[MAX_FRAGS];
    unsigned long irqflags;
    gxio_mpipe_edesc_t edesc = { { 0 } };
    unsigned int i;
    s64 slot;

    if (skb_is_gso(skb))
        return tile_net_tx_tso(skb, dev);

    num_edescs = tile_net_tx_frags(frags, skb, data, skb_headlen(skb));

    /* This is only used to specify the TLB. */
    edesc.stack_idx = large_buffer_stack;

    /* Prepare the edescs. */
    for (i = 0; i < num_edescs; i++) {
        edesc.xfer_size = frags[i].length;
        edesc.va = va_to_tile_io_addr(frags[i].buf);
        edescs[i] = edesc;
    }

    /* Mark the final edesc. */
    edescs[num_edescs - 1].bound = 1;

    /* Add checksum info to the initial edesc, if needed. */
    if (skb->ip_summed == CHECKSUM_PARTIAL) {
        unsigned int csum_start = skb_checksum_start_offset(skb);
        edescs[0].csum = 1;
        edescs[0].csum_start = csum_start;
        edescs[0].csum_dest = csum_start + skb->csum_offset;
    }

    local_irq_save(irqflags);

    /* Try to acquire a completion entry and an egress slot. */
    slot = tile_net_equeue_try_reserve(dev, skb->queue_mapping, comps,
                       equeue, num_edescs);
    if (slot < 0) {
        local_irq_restore(irqflags);
        return NETDEV_TX_BUSY;
    }

    for (i = 0; i < num_edescs; i++)
        gxio_mpipe_equeue_put_at(equeue, edescs[i], slot++);

    /* Add a completion record. */
    add_comp(equeue, comps, slot - 1, skb);

    /* NOTE: Use ETH_ZLEN for short packets (e.g. 42 < 60). */
    tile_net_stats_add(1, &priv->stats.tx_packets);
    tile_net_stats_add(max_t(unsigned int, len, ETH_ZLEN),
               &priv->stats.tx_bytes);

    local_irq_restore(irqflags);

    /* Make sure the egress timer is scheduled. */
    tile_net_schedule_egress_timer();

    return NETDEV_TX_OK;
}

/* Return subqueue id on this core (one per core). */
static u16 tile_net_select_queue(struct net_device *dev, struct sk_buff *skb)
{
    return smp_processor_id();
}

/* Deal with a transmit timeout. */
static void tile_net_tx_timeout(struct net_device *dev)
{
    int cpu;

    for_each_online_cpu(cpu)
        netif_wake_subqueue(dev, cpu);
}

/* Ioctl commands. */
static int tile_net_ioctl(struct net_device *dev, struct ifreq *rq, int cmd)
{
    return -EOPNOTSUPP;
}

/* Get system network statistics for device. */
static struct net_device_stats *tile_net_get_stats(struct net_device *dev)
{
    struct tile_net_priv *priv = netdev_priv(dev);
    return &priv->stats;
}

/* Change the MTU. */
static int tile_net_change_mtu(struct net_device *dev, int new_mtu)
{
    if ((new_mtu < 68) || (new_mtu > 1500))
        return -EINVAL;
    dev->mtu = new_mtu;
    return 0;
}

/* Change the Ethernet address of the NIC.
 *
 * The hypervisor driver does not support changing MAC address.  However,
 * the hardware does not do anything with the MAC address, so the address
 * which gets used on outgoing packets, and which is accepted on incoming
 * packets, is completely up to us.
 *
 * Returns 0 on success, negative on failure.
 */
static int tile_net_set_mac_address(struct net_device *dev, void *p)
{
    struct sockaddr *addr = p;

    if (!is_valid_ether_addr(addr->sa_data))
        return -EINVAL;
    memcpy(dev->dev_addr, addr->sa_data, dev->addr_len);
    return 0;
}

#ifdef CONFIG_NET_POLL_CONTROLLER
/* Polling 'interrupt' - used by things like netconsole to send skbs
 * without having to re-enable interrupts. It's not called while
 * the interrupt routine is executing.
 */
static void tile_net_netpoll(struct net_device *dev)
{
    disable_percpu_irq(ingress_irq);
    tile_net_handle_ingress_irq(ingress_irq, NULL);
    enable_percpu_irq(ingress_irq, 0);
}
#endif

static const struct net_device_ops tile_net_ops = {
    .ndo_open = tile_net_open,
    .ndo_stop = tile_net_stop,
    .ndo_start_xmit = tile_net_tx,
    .ndo_select_queue = tile_net_select_queue,
    .ndo_do_ioctl = tile_net_ioctl,
    .ndo_get_stats = tile_net_get_stats,
    .ndo_change_mtu = tile_net_change_mtu,
    .ndo_tx_timeout = tile_net_tx_timeout,
    .ndo_set_mac_address = tile_net_set_mac_address,
#ifdef CONFIG_NET_POLL_CONTROLLER
    .ndo_poll_controller = tile_net_netpoll,
#endif
};

/* The setup function.
 *
 * This uses ether_setup() to assign various fields in dev, including
 * setting IFF_BROADCAST and IFF_MULTICAST, then sets some extra fields.
 */
static void tile_net_setup(struct net_device *dev)
{
    ether_setup(dev);
    dev->netdev_ops = &tile_net_ops;
    dev->watchdog_timeo = TILE_NET_TIMEOUT;
    dev->features |= NETIF_F_LLTX;
    dev->features |= NETIF_F_HW_CSUM;
    dev->features |= NETIF_F_SG;
    dev->features |= NETIF_F_TSO;
    dev->mtu = 1500;
}

/* Allocate the device structure, register the device, and obtain the
 * MAC address from the hypervisor.
 */
static void tile_net_dev_init(const char *name, const uint8_t *mac)
{
    int ret;
    int i;
    int nz_addr = 0;
    struct net_device *dev;
    struct tile_net_priv *priv;

    /* HACK: Ignore "loop" links. */
    if (strncmp(name, "loop", 4) == 0)
        return;

    /* Allocate the device structure.  Normally, "name" is a
     * template, instantiated by register_netdev(), but not for us.
     */
    dev = alloc_netdev_mqs(sizeof(*priv), name, tile_net_setup,
                   NR_CPUS, 1);
    if (!dev) {
        pr_err("alloc_netdev_mqs(%s) failed\n", name);
        return;
    }

    /* Initialize "priv". */
    priv = netdev_priv(dev);
    memset(priv, 0, sizeof(*priv));
    priv->dev = dev;
    priv->channel = -1;
    priv->loopify_channel = -1;
    priv->echannel = -1;

    /* Get the MAC address and set it in the device struct; this must
     * be done before the device is opened.  If the MAC is all zeroes,
     * we use a random address, since we're probably on the simulator.
     */
    for (i = 0; i < 6; i++)
        nz_addr |= mac[i];

    if (nz_addr) {
        memcpy(dev->dev_addr, mac, 6);
        dev->addr_len = 6;
    } else {
        eth_hw_addr_random(dev);
    }

    /* Register the network device. */
    ret = register_netdev(dev);
    if (ret) {
        netdev_err(dev, "register_netdev failed %d\n", ret);
        free_netdev(dev);
        return;
    }
}

/* Per-cpu module initialization. */
static void tile_net_init_module_percpu(void *unused)
{
    struct tile_net_info *info = &__get_cpu_var(per_cpu_info);
    int my_cpu = smp_processor_id();

    info->has_iqueue = false;

    info->my_cpu = my_cpu;

    /* Initialize the egress timer. */
    hrtimer_init(&info->egress_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
    info->egress_timer.function = tile_net_handle_egress_timer;
}

/* Module initialization. */
static int __init tile_net_init_module(void)
{
    int i;
    char name[GXIO_MPIPE_LINK_NAME_LEN];
    uint8_t mac[6];

    pr_info("Tilera Network Driver\n");

    mutex_init(&tile_net_devs_for_channel_mutex);

    /* Initialize each CPU. */
    on_each_cpu(tile_net_init_module_percpu, NULL, 1);

    /* Find out what devices we have, and initialize them. */
    for (i = 0; gxio_mpipe_link_enumerate_mac(i, name, mac) >= 0; i++)
        tile_net_dev_init(name, mac);

    if (!network_cpus_init())
        network_cpus_map = *cpu_online_mask;

    return 0;
}

module_init(tile_net_init_module);