text: /*
   * 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);
  