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[linux-rt-nao.git] / drivers / net / sfc / tx.c

/****************************************************************************
 * Driver for Solarflare Solarstorm network controllers and boards
 * Copyright 2005-2006 Fen Systems Ltd.
 * Copyright 2005-2008 Solarflare Communications Inc.
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 as published
 * by the Free Software Foundation, incorporated herein by reference.
 */

#include <linux/pci.h>
#include <linux/tcp.h>
#include <linux/ip.h>
#include <linux/in.h>
#include <linux/if_ether.h>
#include <linux/highmem.h>
#include "net_driver.h"
#include "tx.h"
#include "efx.h"
#include "falcon.h"
#include "workarounds.h"

/*
 * TX descriptor ring full threshold
 *
 * The tx_queue descriptor ring fill-level must fall below this value
 * before we restart the netif queue
 */
#define EFX_NETDEV_TX_THRESHOLD(_tx_queue)      \
        (_tx_queue->efx->type->txd_ring_mask / 2u)

/* We want to be able to nest calls to netif_stop_queue(), since each
 * channel can have an individual stop on the queue.
 */
void efx_stop_queue(struct efx_nic *efx)
{
        spin_lock_bh(&efx->netif_stop_lock);
        EFX_TRACE(efx, "stop TX queue\n");

        atomic_inc(&efx->netif_stop_count);
        netif_stop_queue(efx->net_dev);

        spin_unlock_bh(&efx->netif_stop_lock);
}

/* Wake netif's TX queue
 * We want to be able to nest calls to netif_stop_queue(), since each
 * channel can have an individual stop on the queue.
 */
void efx_wake_queue(struct efx_nic *efx)
{
        local_bh_disable();
        if (atomic_dec_and_lock(&efx->netif_stop_count,
                                &efx->netif_stop_lock)) {
                EFX_TRACE(efx, "waking TX queue\n");
                netif_wake_queue(efx->net_dev);
                spin_unlock(&efx->netif_stop_lock);
        }
        local_bh_enable();
}

static void efx_dequeue_buffer(struct efx_tx_queue *tx_queue,
                               struct efx_tx_buffer *buffer)
{
        if (buffer->unmap_len) {
                struct pci_dev *pci_dev = tx_queue->efx->pci_dev;
                dma_addr_t unmap_addr = (buffer->dma_addr + buffer->len -
                                         buffer->unmap_len);
                if (buffer->unmap_single)
                        pci_unmap_single(pci_dev, unmap_addr, buffer->unmap_len,
                                         PCI_DMA_TODEVICE);
                else
                        pci_unmap_page(pci_dev, unmap_addr, buffer->unmap_len,
                                       PCI_DMA_TODEVICE);
                buffer->unmap_len = 0;
                buffer->unmap_single = false;
        }

        if (buffer->skb) {
                dev_kfree_skb_any((struct sk_buff *) buffer->skb);
                buffer->skb = NULL;
                EFX_TRACE(tx_queue->efx, "TX queue %d transmission id %x "
                          "complete\n", tx_queue->queue, read_ptr);
        }
}

/**
 * struct efx_tso_header - a DMA mapped buffer for packet headers
 * @next: Linked list of free ones.
 *      The list is protected by the TX queue lock.
 * @dma_unmap_len: Length to unmap for an oversize buffer, or 0.
 * @dma_addr: The DMA address of the header below.
 *
 * This controls the memory used for a TSO header.  Use TSOH_DATA()
 * to find the packet header data.  Use TSOH_SIZE() to calculate the
 * total size required for a given packet header length.  TSO headers
 * in the free list are exactly %TSOH_STD_SIZE bytes in size.
 */
struct efx_tso_header {
        union {
                struct efx_tso_header *next;
                size_t unmap_len;
        };
        dma_addr_t dma_addr;
};

static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
                               struct sk_buff *skb);
static void efx_fini_tso(struct efx_tx_queue *tx_queue);
static void efx_tsoh_heap_free(struct efx_tx_queue *tx_queue,
                               struct efx_tso_header *tsoh);

static void efx_tsoh_free(struct efx_tx_queue *tx_queue,
                          struct efx_tx_buffer *buffer)
{
        if (buffer->tsoh) {
                if (likely(!buffer->tsoh->unmap_len)) {
                        buffer->tsoh->next = tx_queue->tso_headers_free;
                        tx_queue->tso_headers_free = buffer->tsoh;
                } else {
                        efx_tsoh_heap_free(tx_queue, buffer->tsoh);
                }
                buffer->tsoh = NULL;
        }
}


/*
 * Add a socket buffer to a TX queue
 *
 * This maps all fragments of a socket buffer for DMA and adds them to
 * the TX queue.  The queue's insert pointer will be incremented by
 * the number of fragments in the socket buffer.
 *
 * If any DMA mapping fails, any mapped fragments will be unmapped,
 * the queue's insert pointer will be restored to its original value.
 *
 * Returns NETDEV_TX_OK or NETDEV_TX_BUSY
 * You must hold netif_tx_lock() to call this function.
 */
static int efx_enqueue_skb(struct efx_tx_queue *tx_queue,
                           struct sk_buff *skb)
{
        struct efx_nic *efx = tx_queue->efx;
        struct pci_dev *pci_dev = efx->pci_dev;
        struct efx_tx_buffer *buffer;
        skb_frag_t *fragment;
        struct page *page;
        int page_offset;
        unsigned int len, unmap_len = 0, fill_level, insert_ptr, misalign;
        dma_addr_t dma_addr, unmap_addr = 0;
        unsigned int dma_len;
        bool unmap_single;
        int q_space, i = 0;
        int rc = NETDEV_TX_OK;

        EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);

        if (skb_shinfo((struct sk_buff *)skb)->gso_size)
                return efx_enqueue_skb_tso(tx_queue, skb);

        /* Get size of the initial fragment */
        len = skb_headlen(skb);

        fill_level = tx_queue->insert_count - tx_queue->old_read_count;
        q_space = efx->type->txd_ring_mask - 1 - fill_level;

        /* Map for DMA.  Use pci_map_single rather than pci_map_page
         * since this is more efficient on machines with sparse
         * memory.
         */
        unmap_single = true;
        dma_addr = pci_map_single(pci_dev, skb->data, len, PCI_DMA_TODEVICE);

        /* Process all fragments */
        while (1) {
                if (unlikely(pci_dma_mapping_error(pci_dev, dma_addr)))
                        goto pci_err;

                /* Store fields for marking in the per-fragment final
                 * descriptor */
                unmap_len = len;
                unmap_addr = dma_addr;

                /* Add to TX queue, splitting across DMA boundaries */
                do {
                        if (unlikely(q_space-- <= 0)) {
                                /* It might be that completions have
                                 * happened since the xmit path last
                                 * checked.  Update the xmit path's
                                 * copy of read_count.
                                 */
                                ++tx_queue->stopped;
                                /* This memory barrier protects the
                                 * change of stopped from the access
                                 * of read_count. */
                                smp_mb();
                                tx_queue->old_read_count =
                                        *(volatile unsigned *)
                                        &tx_queue->read_count;
                                fill_level = (tx_queue->insert_count
                                              - tx_queue->old_read_count);
                                q_space = (efx->type->txd_ring_mask - 1 -
                                           fill_level);
                                if (unlikely(q_space-- <= 0))
                                        goto stop;
                                smp_mb();
                                --tx_queue->stopped;
                        }

                        insert_ptr = (tx_queue->insert_count &
                                      efx->type->txd_ring_mask);
                        buffer = &tx_queue->buffer[insert_ptr];
                        efx_tsoh_free(tx_queue, buffer);
                        EFX_BUG_ON_PARANOID(buffer->tsoh);
                        EFX_BUG_ON_PARANOID(buffer->skb);
                        EFX_BUG_ON_PARANOID(buffer->len);
                        EFX_BUG_ON_PARANOID(!buffer->continuation);
                        EFX_BUG_ON_PARANOID(buffer->unmap_len);

                        dma_len = (((~dma_addr) & efx->type->tx_dma_mask) + 1);
                        if (likely(dma_len > len))
                                dma_len = len;

                        misalign = (unsigned)dma_addr & efx->type->bug5391_mask;
                        if (misalign && dma_len + misalign > 512)
                                dma_len = 512 - misalign;

                        /* Fill out per descriptor fields */
                        buffer->len = dma_len;
                        buffer->dma_addr = dma_addr;
                        len -= dma_len;
                        dma_addr += dma_len;
                        ++tx_queue->insert_count;
                } while (len);

                /* Transfer ownership of the unmapping to the final buffer */
                buffer->unmap_single = unmap_single;
                buffer->unmap_len = unmap_len;
                unmap_len = 0;

                /* Get address and size of next fragment */
                if (i >= skb_shinfo(skb)->nr_frags)
                        break;
                fragment = &skb_shinfo(skb)->frags[i];
                len = fragment->size;
                page = fragment->page;
                page_offset = fragment->page_offset;
                i++;
                /* Map for DMA */
                unmap_single = false;
                dma_addr = pci_map_page(pci_dev, page, page_offset, len,
                                        PCI_DMA_TODEVICE);
        }

        /* Transfer ownership of the skb to the final buffer */
        buffer->skb = skb;
        buffer->continuation = false;

        /* Pass off to hardware */
        falcon_push_buffers(tx_queue);

        return NETDEV_TX_OK;

 pci_err:
        EFX_ERR_RL(efx, " TX queue %d could not map skb with %d bytes %d "
                   "fragments for DMA\n", tx_queue->queue, skb->len,
                   skb_shinfo(skb)->nr_frags + 1);

        /* Mark the packet as transmitted, and free the SKB ourselves */
        dev_kfree_skb_any((struct sk_buff *)skb);
        goto unwind;

 stop:
        rc = NETDEV_TX_BUSY;

        if (tx_queue->stopped == 1)
                efx_stop_queue(efx);

 unwind:
        /* Work backwards until we hit the original insert pointer value */
        while (tx_queue->insert_count != tx_queue->write_count) {
                --tx_queue->insert_count;
                insert_ptr = tx_queue->insert_count & efx->type->txd_ring_mask;
                buffer = &tx_queue->buffer[insert_ptr];
                efx_dequeue_buffer(tx_queue, buffer);
                buffer->len = 0;
        }

        /* Free the fragment we were mid-way through pushing */
        if (unmap_len) {
                if (unmap_single)
                        pci_unmap_single(pci_dev, unmap_addr, unmap_len,
                                         PCI_DMA_TODEVICE);
                else
                        pci_unmap_page(pci_dev, unmap_addr, unmap_len,
                                       PCI_DMA_TODEVICE);
        }

        return rc;
}

/* Remove packets from the TX queue
 *
 * This removes packets from the TX queue, up to and including the
 * specified index.
 */
static void efx_dequeue_buffers(struct efx_tx_queue *tx_queue,
                                unsigned int index)
{
        struct efx_nic *efx = tx_queue->efx;
        unsigned int stop_index, read_ptr;
        unsigned int mask = tx_queue->efx->type->txd_ring_mask;

        stop_index = (index + 1) & mask;
        read_ptr = tx_queue->read_count & mask;

        while (read_ptr != stop_index) {
                struct efx_tx_buffer *buffer = &tx_queue->buffer[read_ptr];
                if (unlikely(buffer->len == 0)) {
                        EFX_ERR(tx_queue->efx, "TX queue %d spurious TX "
                                "completion id %x\n", tx_queue->queue,
                                read_ptr);
                        efx_schedule_reset(efx, RESET_TYPE_TX_SKIP);
                        return;
                }

                efx_dequeue_buffer(tx_queue, buffer);
                buffer->continuation = true;
                buffer->len = 0;

                ++tx_queue->read_count;
                read_ptr = tx_queue->read_count & mask;
        }
}

/* Initiate a packet transmission on the specified TX queue.
 * Note that returning anything other than NETDEV_TX_OK will cause the
 * OS to free the skb.
 *
 * This function is split out from efx_hard_start_xmit to allow the
 * loopback test to direct packets via specific TX queues.  It is
 * therefore a non-static inline, so as not to penalise performance
 * for non-loopback transmissions.
 *
 * Context: netif_tx_lock held
 */
inline int efx_xmit(struct efx_nic *efx,
                    struct efx_tx_queue *tx_queue, struct sk_buff *skb)
{
        int rc;

        /* Map fragments for DMA and add to TX queue */
        rc = efx_enqueue_skb(tx_queue, skb);
        if (unlikely(rc != NETDEV_TX_OK))
                goto out;

        /* Update last TX timer */
        efx->net_dev->trans_start = jiffies;

 out:
        return rc;
}

/* Initiate a packet transmission.  We use one channel per CPU
 * (sharing when we have more CPUs than channels).  On Falcon, the TX
 * completion events will be directed back to the CPU that transmitted
 * the packet, which should be cache-efficient.
 *
 * Context: non-blocking.
 * Note that returning anything other than NETDEV_TX_OK will cause the
 * OS to free the skb.
 */
int efx_hard_start_xmit(struct sk_buff *skb, struct net_device *net_dev)
{
        struct efx_nic *efx = netdev_priv(net_dev);
        struct efx_tx_queue *tx_queue;

        if (likely(skb->ip_summed == CHECKSUM_PARTIAL))
                tx_queue = &efx->tx_queue[EFX_TX_QUEUE_OFFLOAD_CSUM];
        else
                tx_queue = &efx->tx_queue[EFX_TX_QUEUE_NO_CSUM];

        return efx_xmit(efx, tx_queue, skb);
}

void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index)
{
        unsigned fill_level;
        struct efx_nic *efx = tx_queue->efx;

        EFX_BUG_ON_PARANOID(index > efx->type->txd_ring_mask);

        efx_dequeue_buffers(tx_queue, index);

        /* See if we need to restart the netif queue.  This barrier
         * separates the update of read_count from the test of
         * stopped. */
        smp_mb();
        if (unlikely(tx_queue->stopped)) {
                fill_level = tx_queue->insert_count - tx_queue->read_count;
                if (fill_level < EFX_NETDEV_TX_THRESHOLD(tx_queue)) {
                        EFX_BUG_ON_PARANOID(!efx_dev_registered(efx));

                        /* Do this under netif_tx_lock(), to avoid racing
                         * with efx_xmit(). */
                        netif_tx_lock(efx->net_dev);
                        if (tx_queue->stopped) {
                                tx_queue->stopped = 0;
                                efx_wake_queue(efx);
                        }
                        netif_tx_unlock(efx->net_dev);
                }
        }
}

int efx_probe_tx_queue(struct efx_tx_queue *tx_queue)
{
        struct efx_nic *efx = tx_queue->efx;
        unsigned int txq_size;
        int i, rc;

        EFX_LOG(efx, "creating TX queue %d\n", tx_queue->queue);

        /* Allocate software ring */
        txq_size = (efx->type->txd_ring_mask + 1) * sizeof(*tx_queue->buffer);
        tx_queue->buffer = kzalloc(txq_size, GFP_KERNEL);
        if (!tx_queue->buffer)
                return -ENOMEM;
        for (i = 0; i <= efx->type->txd_ring_mask; ++i)
                tx_queue->buffer[i].continuation = true;

        /* Allocate hardware ring */
        rc = falcon_probe_tx(tx_queue);
        if (rc)
                goto fail;

        return 0;

 fail:
        kfree(tx_queue->buffer);
        tx_queue->buffer = NULL;
        return rc;
}

void efx_init_tx_queue(struct efx_tx_queue *tx_queue)
{
        EFX_LOG(tx_queue->efx, "initialising TX queue %d\n", tx_queue->queue);

        tx_queue->insert_count = 0;
        tx_queue->write_count = 0;
        tx_queue->read_count = 0;
        tx_queue->old_read_count = 0;
        BUG_ON(tx_queue->stopped);

        /* Set up TX descriptor ring */
        falcon_init_tx(tx_queue);
}

void efx_release_tx_buffers(struct efx_tx_queue *tx_queue)
{
        struct efx_tx_buffer *buffer;

        if (!tx_queue->buffer)
                return;

        /* Free any buffers left in the ring */
        while (tx_queue->read_count != tx_queue->write_count) {
                buffer = &tx_queue->buffer[tx_queue->read_count &
                                           tx_queue->efx->type->txd_ring_mask];
                efx_dequeue_buffer(tx_queue, buffer);
                buffer->continuation = true;
                buffer->len = 0;

                ++tx_queue->read_count;
        }
}

void efx_fini_tx_queue(struct efx_tx_queue *tx_queue)
{
        EFX_LOG(tx_queue->efx, "shutting down TX queue %d\n", tx_queue->queue);

        /* Flush TX queue, remove descriptor ring */
        falcon_fini_tx(tx_queue);

        efx_release_tx_buffers(tx_queue);

        /* Free up TSO header cache */
        efx_fini_tso(tx_queue);

        /* Release queue's stop on port, if any */
        if (tx_queue->stopped) {
                tx_queue->stopped = 0;
                efx_wake_queue(tx_queue->efx);
        }
}

void efx_remove_tx_queue(struct efx_tx_queue *tx_queue)
{
        EFX_LOG(tx_queue->efx, "destroying TX queue %d\n", tx_queue->queue);
        falcon_remove_tx(tx_queue);

        kfree(tx_queue->buffer);
        tx_queue->buffer = NULL;
}


/* Efx TCP segmentation acceleration.
 *
 * Why?  Because by doing it here in the driver we can go significantly
 * faster than the GSO.
 *
 * Requires TX checksum offload support.
 */

/* Number of bytes inserted at the start of a TSO header buffer,
 * similar to NET_IP_ALIGN.
 */
#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
#define TSOH_OFFSET     0
#else
#define TSOH_OFFSET     NET_IP_ALIGN
#endif

#define TSOH_BUFFER(tsoh)       ((u8 *)(tsoh + 1) + TSOH_OFFSET)

/* Total size of struct efx_tso_header, buffer and padding */
#define TSOH_SIZE(hdr_len)                                      \
        (sizeof(struct efx_tso_header) + TSOH_OFFSET + hdr_len)

/* Size of blocks on free list.  Larger blocks must be allocated from
 * the heap.
 */
#define TSOH_STD_SIZE           128

#define PTR_DIFF(p1, p2)  ((u8 *)(p1) - (u8 *)(p2))
#define ETH_HDR_LEN(skb)  (skb_network_header(skb) - (skb)->data)
#define SKB_TCP_OFF(skb)  PTR_DIFF(tcp_hdr(skb), (skb)->data)
#define SKB_IPV4_OFF(skb) PTR_DIFF(ip_hdr(skb), (skb)->data)

/**
 * struct tso_state - TSO state for an SKB
 * @out_len: Remaining length in current segment
 * @seqnum: Current sequence number
 * @ipv4_id: Current IPv4 ID, host endian
 * @packet_space: Remaining space in current packet
 * @dma_addr: DMA address of current position
 * @in_len: Remaining length in current SKB fragment
 * @unmap_len: Length of SKB fragment
 * @unmap_addr: DMA address of SKB fragment
 * @unmap_single: DMA single vs page mapping flag
 * @header_len: Number of bytes of header
 * @full_packet_size: Number of bytes to put in each outgoing segment
 *
 * The state used during segmentation.  It is put into this data structure
 * just to make it easy to pass into inline functions.
 */
struct tso_state {
        /* Output position */
        unsigned out_len;
        unsigned seqnum;
        unsigned ipv4_id;
        unsigned packet_space;

        /* Input position */
        dma_addr_t dma_addr;
        unsigned in_len;
        unsigned unmap_len;
        dma_addr_t unmap_addr;
        bool unmap_single;

        unsigned header_len;
        int full_packet_size;
};


/*
 * Verify that our various assumptions about sk_buffs and the conditions
 * under which TSO will be attempted hold true.
 */
static void efx_tso_check_safe(struct sk_buff *skb)
{
        __be16 protocol = skb->protocol;

        EFX_BUG_ON_PARANOID(((struct ethhdr *)skb->data)->h_proto !=
                            protocol);
        if (protocol == htons(ETH_P_8021Q)) {
                /* Find the encapsulated protocol; reset network header
                 * and transport header based on that. */
                struct vlan_ethhdr *veh = (struct vlan_ethhdr *)skb->data;
                protocol = veh->h_vlan_encapsulated_proto;
                skb_set_network_header(skb, sizeof(*veh));
                if (protocol == htons(ETH_P_IP))
                        skb_set_transport_header(skb, sizeof(*veh) +
                                                 4 * ip_hdr(skb)->ihl);
        }

        EFX_BUG_ON_PARANOID(protocol != htons(ETH_P_IP));
        EFX_BUG_ON_PARANOID(ip_hdr(skb)->protocol != IPPROTO_TCP);
        EFX_BUG_ON_PARANOID((PTR_DIFF(tcp_hdr(skb), skb->data)
                             + (tcp_hdr(skb)->doff << 2u)) >
                            skb_headlen(skb));
}


/*
 * Allocate a page worth of efx_tso_header structures, and string them
 * into the tx_queue->tso_headers_free linked list. Return 0 or -ENOMEM.
 */
static int efx_tsoh_block_alloc(struct efx_tx_queue *tx_queue)
{

        struct pci_dev *pci_dev = tx_queue->efx->pci_dev;
        struct efx_tso_header *tsoh;
        dma_addr_t dma_addr;
        u8 *base_kva, *kva;

        base_kva = pci_alloc_consistent(pci_dev, PAGE_SIZE, &dma_addr);
        if (base_kva == NULL) {
                EFX_ERR(tx_queue->efx, "Unable to allocate page for TSO"
                        " headers\n");
                return -ENOMEM;
        }

        /* pci_alloc_consistent() allocates pages. */
        EFX_BUG_ON_PARANOID(dma_addr & (PAGE_SIZE - 1u));

        for (kva = base_kva; kva < base_kva + PAGE_SIZE; kva += TSOH_STD_SIZE) {
                tsoh = (struct efx_tso_header *)kva;
                tsoh->dma_addr = dma_addr + (TSOH_BUFFER(tsoh) - base_kva);
                tsoh->next = tx_queue->tso_headers_free;
                tx_queue->tso_headers_free = tsoh;
        }

        return 0;
}


/* Free up a TSO header, and all others in the same page. */
static void efx_tsoh_block_free(struct efx_tx_queue *tx_queue,
                                struct efx_tso_header *tsoh,
                                struct pci_dev *pci_dev)
{
        struct efx_tso_header **p;
        unsigned long base_kva;
        dma_addr_t base_dma;

        base_kva = (unsigned long)tsoh & PAGE_MASK;
        base_dma = tsoh->dma_addr & PAGE_MASK;

        p = &tx_queue->tso_headers_free;
        while (*p != NULL) {
                if (((unsigned long)*p & PAGE_MASK) == base_kva)
                        *p = (*p)->next;
                else
                        p = &(*p)->next;
        }

        pci_free_consistent(pci_dev, PAGE_SIZE, (void *)base_kva, base_dma);
}

static struct efx_tso_header *
efx_tsoh_heap_alloc(struct efx_tx_queue *tx_queue, size_t header_len)
{
        struct efx_tso_header *tsoh;

        tsoh = kmalloc(TSOH_SIZE(header_len), GFP_ATOMIC | GFP_DMA);
        if (unlikely(!tsoh))
                return NULL;

        tsoh->dma_addr = pci_map_single(tx_queue->efx->pci_dev,
                                        TSOH_BUFFER(tsoh), header_len,
                                        PCI_DMA_TODEVICE);
        if (unlikely(pci_dma_mapping_error(tx_queue->efx->pci_dev,
                                           tsoh->dma_addr))) {
                kfree(tsoh);
                return NULL;
        }

        tsoh->unmap_len = header_len;
        return tsoh;
}

static void
efx_tsoh_heap_free(struct efx_tx_queue *tx_queue, struct efx_tso_header *tsoh)
{
        pci_unmap_single(tx_queue->efx->pci_dev,
                         tsoh->dma_addr, tsoh->unmap_len,
                         PCI_DMA_TODEVICE);
        kfree(tsoh);
}

/**
 * efx_tx_queue_insert - push descriptors onto the TX queue
 * @tx_queue:           Efx TX queue
 * @dma_addr:           DMA address of fragment
 * @len:                Length of fragment
 * @final_buffer:       The final buffer inserted into the queue
 *
 * Push descriptors onto the TX queue.  Return 0 on success or 1 if
 * @tx_queue full.
 */
static int efx_tx_queue_insert(struct efx_tx_queue *tx_queue,
                               dma_addr_t dma_addr, unsigned len,
                               struct efx_tx_buffer **final_buffer)
{
        struct efx_tx_buffer *buffer;
        struct efx_nic *efx = tx_queue->efx;
        unsigned dma_len, fill_level, insert_ptr, misalign;
        int q_space;

        EFX_BUG_ON_PARANOID(len <= 0);

        fill_level = tx_queue->insert_count - tx_queue->old_read_count;
        /* -1 as there is no way to represent all descriptors used */
        q_space = efx->type->txd_ring_mask - 1 - fill_level;

        while (1) {
                if (unlikely(q_space-- <= 0)) {
                        /* It might be that completions have happened
                         * since the xmit path last checked.  Update
                         * the xmit path's copy of read_count.
                         */
                        ++tx_queue->stopped;
                        /* This memory barrier protects the change of
                         * stopped from the access of read_count. */
                        smp_mb();
                        tx_queue->old_read_count =
                                *(volatile unsigned *)&tx_queue->read_count;
                        fill_level = (tx_queue->insert_count
                                      - tx_queue->old_read_count);
                        q_space = efx->type->txd_ring_mask - 1 - fill_level;
                        if (unlikely(q_space-- <= 0)) {
                                *final_buffer = NULL;
                                return 1;
                        }
                        smp_mb();
                        --tx_queue->stopped;
                }

                insert_ptr = tx_queue->insert_count & efx->type->txd_ring_mask;
                buffer = &tx_queue->buffer[insert_ptr];
                ++tx_queue->insert_count;

                EFX_BUG_ON_PARANOID(tx_queue->insert_count -
                                    tx_queue->read_count >
                                    efx->type->txd_ring_mask);

                efx_tsoh_free(tx_queue, buffer);
                EFX_BUG_ON_PARANOID(buffer->len);
                EFX_BUG_ON_PARANOID(buffer->unmap_len);
                EFX_BUG_ON_PARANOID(buffer->skb);
                EFX_BUG_ON_PARANOID(!buffer->continuation);
                EFX_BUG_ON_PARANOID(buffer->tsoh);

                buffer->dma_addr = dma_addr;

                /* Ensure we do not cross a boundary unsupported by H/W */
                dma_len = (~dma_addr & efx->type->tx_dma_mask) + 1;

                misalign = (unsigned)dma_addr & efx->type->bug5391_mask;
                if (misalign && dma_len + misalign > 512)
                        dma_len = 512 - misalign;

                /* If there is enough space to send then do so */
                if (dma_len >= len)
                        break;

                buffer->len = dma_len; /* Don't set the other members */
                dma_addr += dma_len;
                len -= dma_len;
        }

        EFX_BUG_ON_PARANOID(!len);
        buffer->len = len;
        *final_buffer = buffer;
        return 0;
}


/*
 * Put a TSO header into the TX queue.
 *
 * This is special-cased because we know that it is small enough to fit in
 * a single fragment, and we know it doesn't cross a page boundary.  It
 * also allows us to not worry about end-of-packet etc.
 */
static void efx_tso_put_header(struct efx_tx_queue *tx_queue,
                               struct efx_tso_header *tsoh, unsigned len)
{
        struct efx_tx_buffer *buffer;

        buffer = &tx_queue->buffer[tx_queue->insert_count &
                                   tx_queue->efx->type->txd_ring_mask];
        efx_tsoh_free(tx_queue, buffer);
        EFX_BUG_ON_PARANOID(buffer->len);
        EFX_BUG_ON_PARANOID(buffer->unmap_len);
        EFX_BUG_ON_PARANOID(buffer->skb);
        EFX_BUG_ON_PARANOID(!buffer->continuation);
        EFX_BUG_ON_PARANOID(buffer->tsoh);
        buffer->len = len;
        buffer->dma_addr = tsoh->dma_addr;
        buffer->tsoh = tsoh;

        ++tx_queue->insert_count;
}


/* Remove descriptors put into a tx_queue. */
static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue)
{
        struct efx_tx_buffer *buffer;
        dma_addr_t unmap_addr;

        /* Work backwards until we hit the original insert pointer value */
        while (tx_queue->insert_count != tx_queue->write_count) {
                --tx_queue->insert_count;
                buffer = &tx_queue->buffer[tx_queue->insert_count &
                                           tx_queue->efx->type->txd_ring_mask];
                efx_tsoh_free(tx_queue, buffer);
                EFX_BUG_ON_PARANOID(buffer->skb);
                buffer->len = 0;
                buffer->continuation = true;
                if (buffer->unmap_len) {
                        unmap_addr = (buffer->dma_addr + buffer->len -
                                      buffer->unmap_len);
                        if (buffer->unmap_single)
                                pci_unmap_single(tx_queue->efx->pci_dev,
                                                 unmap_addr, buffer->unmap_len,
                                                 PCI_DMA_TODEVICE);
                        else
                                pci_unmap_page(tx_queue->efx->pci_dev,
                                               unmap_addr, buffer->unmap_len,
                                               PCI_DMA_TODEVICE);
                        buffer->unmap_len = 0;
                }
        }
}


/* Parse the SKB header and initialise state. */
static void tso_start(struct tso_state *st, const struct sk_buff *skb)
{
        /* All ethernet/IP/TCP headers combined size is TCP header size
         * plus offset of TCP header relative to start of packet.
         */
        st->header_len = ((tcp_hdr(skb)->doff << 2u)
                          + PTR_DIFF(tcp_hdr(skb), skb->data));
        st->full_packet_size = st->header_len + skb_shinfo(skb)->gso_size;

        st->ipv4_id = ntohs(ip_hdr(skb)->id);
        st->seqnum = ntohl(tcp_hdr(skb)->seq);

        EFX_BUG_ON_PARANOID(tcp_hdr(skb)->urg);
        EFX_BUG_ON_PARANOID(tcp_hdr(skb)->syn);
        EFX_BUG_ON_PARANOID(tcp_hdr(skb)->rst);

        st->packet_space = st->full_packet_size;
        st->out_len = skb->len - st->header_len;
        st->unmap_len = 0;
        st->unmap_single = false;
}

static int tso_get_fragment(struct tso_state *st, struct efx_nic *efx,
                            skb_frag_t *frag)
{
        st->unmap_addr = pci_map_page(efx->pci_dev, frag->page,
                                      frag->page_offset, frag->size,
                                      PCI_DMA_TODEVICE);
        if (likely(!pci_dma_mapping_error(efx->pci_dev, st->unmap_addr))) {
                st->unmap_single = false;
                st->unmap_len = frag->size;
                st->in_len = frag->size;
                st->dma_addr = st->unmap_addr;
                return 0;
        }
        return -ENOMEM;
}

static int tso_get_head_fragment(struct tso_state *st, struct efx_nic *efx,
                                 const struct sk_buff *skb)
{
        int hl = st->header_len;
        int len = skb_headlen(skb) - hl;

        st->unmap_addr = pci_map_single(efx->pci_dev, skb->data + hl,
                                        len, PCI_DMA_TODEVICE);
        if (likely(!pci_dma_mapping_error(efx->pci_dev, st->unmap_addr))) {
                st->unmap_single = true;
                st->unmap_len = len;
                st->in_len = len;
                st->dma_addr = st->unmap_addr;
                return 0;
        }
        return -ENOMEM;
}


/**
 * tso_fill_packet_with_fragment - form descriptors for the current fragment
 * @tx_queue:           Efx TX queue
 * @skb:                Socket buffer
 * @st:                 TSO state
 *
 * Form descriptors for the current fragment, until we reach the end
 * of fragment or end-of-packet.  Return 0 on success, 1 if not enough
 * space in @tx_queue.
 */
static int tso_fill_packet_with_fragment(struct efx_tx_queue *tx_queue,
                                         const struct sk_buff *skb,
                                         struct tso_state *st)
{
        struct efx_tx_buffer *buffer;
        int n, end_of_packet, rc;

        if (st->in_len == 0)
                return 0;
        if (st->packet_space == 0)
                return 0;

        EFX_BUG_ON_PARANOID(st->in_len <= 0);
        EFX_BUG_ON_PARANOID(st->packet_space <= 0);

        n = min(st->in_len, st->packet_space);

        st->packet_space -= n;
        st->out_len -= n;
        st->in_len -= n;

        rc = efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);
        if (likely(rc == 0)) {
                if (st->out_len == 0)
                        /* Transfer ownership of the skb */
                        buffer->skb = skb;

                end_of_packet = st->out_len == 0 || st->packet_space == 0;
                buffer->continuation = !end_of_packet;

                if (st->in_len == 0) {
                        /* Transfer ownership of the pci mapping */
                        buffer->unmap_len = st->unmap_len;
                        buffer->unmap_single = st->unmap_single;
                        st->unmap_len = 0;
                }
        }

        st->dma_addr += n;
        return rc;
}


/**
 * tso_start_new_packet - generate a new header and prepare for the new packet
 * @tx_queue:           Efx TX queue
 * @skb:                Socket buffer
 * @st:                 TSO state
 *
 * Generate a new header and prepare for the new packet.  Return 0 on
 * success, or -1 if failed to alloc header.
 */
static int tso_start_new_packet(struct efx_tx_queue *tx_queue,
                                const struct sk_buff *skb,
                                struct tso_state *st)
{
        struct efx_tso_header *tsoh;
        struct iphdr *tsoh_iph;
        struct tcphdr *tsoh_th;
        unsigned ip_length;
        u8 *header;

        /* Allocate a DMA-mapped header buffer. */
        if (likely(TSOH_SIZE(st->header_len) <= TSOH_STD_SIZE)) {
                if (tx_queue->tso_headers_free == NULL) {
                        if (efx_tsoh_block_alloc(tx_queue))
                                return -1;
                }
                EFX_BUG_ON_PARANOID(!tx_queue->tso_headers_free);
                tsoh = tx_queue->tso_headers_free;
                tx_queue->tso_headers_free = tsoh->next;
                tsoh->unmap_len = 0;
        } else {
                tx_queue->tso_long_headers++;
                tsoh = efx_tsoh_heap_alloc(tx_queue, st->header_len);
                if (unlikely(!tsoh))
                        return -1;
        }

        header = TSOH_BUFFER(tsoh);
        tsoh_th = (struct tcphdr *)(header + SKB_TCP_OFF(skb));
        tsoh_iph = (struct iphdr *)(header + SKB_IPV4_OFF(skb));

        /* Copy and update the headers. */
        memcpy(header, skb->data, st->header_len);

        tsoh_th->seq = htonl(st->seqnum);
        st->seqnum += skb_shinfo(skb)->gso_size;
        if (st->out_len > skb_shinfo(skb)->gso_size) {
                /* This packet will not finish the TSO burst. */
                ip_length = st->full_packet_size - ETH_HDR_LEN(skb);
                tsoh_th->fin = 0;
                tsoh_th->psh = 0;
        } else {
                /* This packet will be the last in the TSO burst. */
                ip_length = st->header_len - ETH_HDR_LEN(skb) + st->out_len;
                tsoh_th->fin = tcp_hdr(skb)->fin;
                tsoh_th->psh = tcp_hdr(skb)->psh;
        }
        tsoh_iph->tot_len = htons(ip_length);

        /* Linux leaves suitable gaps in the IP ID space for us to fill. */
        tsoh_iph->id = htons(st->ipv4_id);
        st->ipv4_id++;

        st->packet_space = skb_shinfo(skb)->gso_size;
        ++tx_queue->tso_packets;

        /* Form a descriptor for this header. */
        efx_tso_put_header(tx_queue, tsoh, st->header_len);

        return 0;
}


/**
 * efx_enqueue_skb_tso - segment and transmit a TSO socket buffer
 * @tx_queue:           Efx TX queue
 * @skb:                Socket buffer
 *
 * Context: You must hold netif_tx_lock() to call this function.
 *
 * Add socket buffer @skb to @tx_queue, doing TSO or return != 0 if
 * @skb was not enqueued.  In all cases @skb is consumed.  Return
 * %NETDEV_TX_OK or %NETDEV_TX_BUSY.
 */
static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
                               struct sk_buff *skb)
{
        struct efx_nic *efx = tx_queue->efx;
        int frag_i, rc, rc2 = NETDEV_TX_OK;
        struct tso_state state;

        /* Verify TSO is safe - these checks should never fail. */
        efx_tso_check_safe(skb);

        EFX_BUG_ON_PARANOID(tx_queue->write_count != tx_queue->insert_count);

        tso_start(&state, skb);

        /* Assume that skb header area contains exactly the headers, and
         * all payload is in the frag list.
         */
        if (skb_headlen(skb) == state.header_len) {
                /* Grab the first payload fragment. */
                EFX_BUG_ON_PARANOID(skb_shinfo(skb)->nr_frags < 1);
                frag_i = 0;
                rc = tso_get_fragment(&state, efx,
                                      skb_shinfo(skb)->frags + frag_i);
                if (rc)
                        goto mem_err;
        } else {
                rc = tso_get_head_fragment(&state, efx, skb);
                if (rc)
                        goto mem_err;
                frag_i = -1;
        }

        if (tso_start_new_packet(tx_queue, skb, &state) < 0)
                goto mem_err;

        while (1) {
                rc = tso_fill_packet_with_fragment(tx_queue, skb, &state);
                if (unlikely(rc))
                        goto stop;

                /* Move onto the next fragment? */
                if (state.in_len == 0) {
                        if (++frag_i >= skb_shinfo(skb)->nr_frags)
                                /* End of payload reached. */
                                break;
                        rc = tso_get_fragment(&state, efx,
                                              skb_shinfo(skb)->frags + frag_i);
                        if (rc)
                                goto mem_err;
                }

                /* Start at new packet? */
                if (state.packet_space == 0 &&
                    tso_start_new_packet(tx_queue, skb, &state) < 0)
                        goto mem_err;
        }

        /* Pass off to hardware */
        falcon_push_buffers(tx_queue);

        tx_queue->tso_bursts++;
        return NETDEV_TX_OK;

 mem_err:
        EFX_ERR(efx, "Out of memory for TSO headers, or PCI mapping error\n");
        dev_kfree_skb_any((struct sk_buff *)skb);
        goto unwind;

 stop:
        rc2 = NETDEV_TX_BUSY;

        /* Stop the queue if it wasn't stopped before. */
        if (tx_queue->stopped == 1)
                efx_stop_queue(efx);

 unwind:
        /* Free the DMA mapping we were in the process of writing out */
        if (state.unmap_len) {
                if (state.unmap_single)
                        pci_unmap_single(efx->pci_dev, state.unmap_addr,
                                         state.unmap_len, PCI_DMA_TODEVICE);
                else
                        pci_unmap_page(efx->pci_dev, state.unmap_addr,
                                       state.unmap_len, PCI_DMA_TODEVICE);
        }

        efx_enqueue_unwind(tx_queue);
        return rc2;
}


/*
 * Free up all TSO datastructures associated with tx_queue. This
 * routine should be called only once the tx_queue is both empty and
 * will no longer be used.
 */
static void efx_fini_tso(struct efx_tx_queue *tx_queue)
{
        unsigned i;

        if (tx_queue->buffer) {
                for (i = 0; i <= tx_queue->efx->type->txd_ring_mask; ++i)
                        efx_tsoh_free(tx_queue, &tx_queue->buffer[i]);
        }

        while (tx_queue->tso_headers_free != NULL)
                efx_tsoh_block_free(tx_queue, tx_queue->tso_headers_free,
                                    tx_queue->efx->pci_dev);
}