net: tilegx driver bugfix (be explicit about percpu queue number)

[GitHub/LineageOS/android_kernel_samsung_universal7580.git] / drivers / net / ethernet / tile / tilegx.c

/*
 * 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, NULL, 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 data_len = skb->data_len;
        unsigned int p_len = sh->gso_size;
        long f_id = -1;    /* id of the current fragment */
        long f_size = -1;  /* size of the current fragment */
        long f_used = -1;  /* 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 = sh->frags[f_id].size;
                                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 data_len = skb->data_len;
        unsigned char *data = skb->data;
        unsigned int ih_off, th_off, sh_len, p_len;
        unsigned int isum_seed, tsum_seed, id, seq;
        long f_id = -1;    /* id of the current fragment */
        long f_size = -1;  /* size of the current fragment */
        long f_used = -1;  /* 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);
        sh_len = th_off + tcp_hdrlen(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 = sh->frags[f_id].size;
                                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 data_len = skb->data_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 = -1;  /* size of the current fragment */
        long f_used = -1;  /* bytes used from the current fragment */
        long n;            /* size of the current piece of payload */
        unsigned long tx_packets = 0, tx_bytes = 0;
        unsigned int csum_start, sh_len;
        int segment;

        /* Prepare to egress the headers: set up header edesc. */
        csum_start = skb_checksum_start_offset(skb);
        sh_len = skb_transport_offset(skb) + tcp_hdrlen(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++) {
                void *va;
                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) {

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

                        va = tile_net_frag_buf(&sh->frags[f_id]) + 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_random_addr(dev->dev_addr);
        }

        /* 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);