Merge tag 'vmwgfx-fixes-3.14-2014-02-18' of git://people.freedesktop.org/~thomash...

[mirror_ubuntu-artful-kernel.git] / drivers / net / ethernet / sfc / tx.c

/****************************************************************************
 * Driver for Solarflare network controllers and boards
 * Copyright 2005-2006 Fen Systems Ltd.
 * Copyright 2005-2013 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/ipv6.h>
#include <linux/slab.h>
#include <net/ipv6.h>
#include <linux/if_ether.h>
#include <linux/highmem.h>
#include <linux/cache.h>
#include "net_driver.h"
#include "efx.h"
#include "io.h"
#include "nic.h"
#include "workarounds.h"
#include "ef10_regs.h"

#ifdef EFX_USE_PIO

#define EFX_PIOBUF_SIZE_MAX ER_DZ_TX_PIOBUF_SIZE
#define EFX_PIOBUF_SIZE_DEF ALIGN(256, L1_CACHE_BYTES)
unsigned int efx_piobuf_size __read_mostly = EFX_PIOBUF_SIZE_DEF;

#endif /* EFX_USE_PIO */

static inline unsigned int
efx_tx_queue_get_insert_index(const struct efx_tx_queue *tx_queue)
{
        return tx_queue->insert_count & tx_queue->ptr_mask;
}

static inline struct efx_tx_buffer *
__efx_tx_queue_get_insert_buffer(const struct efx_tx_queue *tx_queue)
{
        return &tx_queue->buffer[efx_tx_queue_get_insert_index(tx_queue)];
}

static inline struct efx_tx_buffer *
efx_tx_queue_get_insert_buffer(const struct efx_tx_queue *tx_queue)
{
        struct efx_tx_buffer *buffer =
                __efx_tx_queue_get_insert_buffer(tx_queue);

        EFX_BUG_ON_PARANOID(buffer->len);
        EFX_BUG_ON_PARANOID(buffer->flags);
        EFX_BUG_ON_PARANOID(buffer->unmap_len);

        return buffer;
}

static void efx_dequeue_buffer(struct efx_tx_queue *tx_queue,
                               struct efx_tx_buffer *buffer,
                               unsigned int *pkts_compl,
                               unsigned int *bytes_compl)
{
        if (buffer->unmap_len) {
                struct device *dma_dev = &tx_queue->efx->pci_dev->dev;
                dma_addr_t unmap_addr = buffer->dma_addr - buffer->dma_offset;
                if (buffer->flags & EFX_TX_BUF_MAP_SINGLE)
                        dma_unmap_single(dma_dev, unmap_addr, buffer->unmap_len,
                                         DMA_TO_DEVICE);
                else
                        dma_unmap_page(dma_dev, unmap_addr, buffer->unmap_len,
                                       DMA_TO_DEVICE);
                buffer->unmap_len = 0;
        }

        if (buffer->flags & EFX_TX_BUF_SKB) {
                (*pkts_compl)++;
                (*bytes_compl) += buffer->skb->len;
                dev_kfree_skb_any((struct sk_buff *) buffer->skb);
                netif_vdbg(tx_queue->efx, tx_done, tx_queue->efx->net_dev,
                           "TX queue %d transmission id %x complete\n",
                           tx_queue->queue, tx_queue->read_count);
        } else if (buffer->flags & EFX_TX_BUF_HEAP) {
                kfree(buffer->heap_buf);
        }

        buffer->len = 0;
        buffer->flags = 0;
}

static int efx_enqueue_skb_tso(struct efx_tx_queue *tx_queue,
                               struct sk_buff *skb);

static inline unsigned
efx_max_tx_len(struct efx_nic *efx, dma_addr_t dma_addr)
{
        /* Depending on the NIC revision, we can use descriptor
         * lengths up to 8K or 8K-1.  However, since PCI Express
         * devices must split read requests at 4K boundaries, there is
         * little benefit from using descriptors that cross those
         * boundaries and we keep things simple by not doing so.
         */
        unsigned len = (~dma_addr & (EFX_PAGE_SIZE - 1)) + 1;

        /* Work around hardware bug for unaligned buffers. */
        if (EFX_WORKAROUND_5391(efx) && (dma_addr & 0xf))
                len = min_t(unsigned, len, 512 - (dma_addr & 0xf));

        return len;
}

unsigned int efx_tx_max_skb_descs(struct efx_nic *efx)
{
        /* Header and payload descriptor for each output segment, plus
         * one for every input fragment boundary within a segment
         */
        unsigned int max_descs = EFX_TSO_MAX_SEGS * 2 + MAX_SKB_FRAGS;

        /* Possibly one more per segment for the alignment workaround,
         * or for option descriptors
         */
        if (EFX_WORKAROUND_5391(efx) || efx_nic_rev(efx) >= EFX_REV_HUNT_A0)
                max_descs += EFX_TSO_MAX_SEGS;

        /* Possibly more for PCIe page boundaries within input fragments */
        if (PAGE_SIZE > EFX_PAGE_SIZE)
                max_descs += max_t(unsigned int, MAX_SKB_FRAGS,
                                   DIV_ROUND_UP(GSO_MAX_SIZE, EFX_PAGE_SIZE));

        return max_descs;
}

/* Get partner of a TX queue, seen as part of the same net core queue */
static struct efx_tx_queue *efx_tx_queue_partner(struct efx_tx_queue *tx_queue)
{
        if (tx_queue->queue & EFX_TXQ_TYPE_OFFLOAD)
                return tx_queue - EFX_TXQ_TYPE_OFFLOAD;
        else
                return tx_queue + EFX_TXQ_TYPE_OFFLOAD;
}

static void efx_tx_maybe_stop_queue(struct efx_tx_queue *txq1)
{
        /* We need to consider both queues that the net core sees as one */
        struct efx_tx_queue *txq2 = efx_tx_queue_partner(txq1);
        struct efx_nic *efx = txq1->efx;
        unsigned int fill_level;

        fill_level = max(txq1->insert_count - txq1->old_read_count,
                         txq2->insert_count - txq2->old_read_count);
        if (likely(fill_level < efx->txq_stop_thresh))
                return;

        /* We used the stale old_read_count above, which gives us a
         * pessimistic estimate of the fill level (which may even
         * validly be >= efx->txq_entries).  Now try again using
         * read_count (more likely to be a cache miss).
         *
         * If we read read_count and then conditionally stop the
         * queue, it is possible for the completion path to race with
         * us and complete all outstanding descriptors in the middle,
         * after which there will be no more completions to wake it.
         * Therefore we stop the queue first, then read read_count
         * (with a memory barrier to ensure the ordering), then
         * restart the queue if the fill level turns out to be low
         * enough.
         */
        netif_tx_stop_queue(txq1->core_txq);
        smp_mb();
        txq1->old_read_count = ACCESS_ONCE(txq1->read_count);
        txq2->old_read_count = ACCESS_ONCE(txq2->read_count);

        fill_level = max(txq1->insert_count - txq1->old_read_count,
                         txq2->insert_count - txq2->old_read_count);
        EFX_BUG_ON_PARANOID(fill_level >= efx->txq_entries);
        if (likely(fill_level < efx->txq_stop_thresh)) {
                smp_mb();
                if (likely(!efx->loopback_selftest))
                        netif_tx_start_queue(txq1->core_txq);
        }
}

#ifdef EFX_USE_PIO

struct efx_short_copy_buffer {
        int used;
        u8 buf[L1_CACHE_BYTES];
};

/* Copy to PIO, respecting that writes to PIO buffers must be dword aligned.
 * Advances piobuf pointer. Leaves additional data in the copy buffer.
 */
static void efx_memcpy_toio_aligned(struct efx_nic *efx, u8 __iomem **piobuf,
                                    u8 *data, int len,
                                    struct efx_short_copy_buffer *copy_buf)
{
        int block_len = len & ~(sizeof(copy_buf->buf) - 1);

        memcpy_toio(*piobuf, data, block_len);
        *piobuf += block_len;
        len -= block_len;

        if (len) {
                data += block_len;
                BUG_ON(copy_buf->used);
                BUG_ON(len > sizeof(copy_buf->buf));
                memcpy(copy_buf->buf, data, len);
                copy_buf->used = len;
        }
}

/* Copy to PIO, respecting dword alignment, popping data from copy buffer first.
 * Advances piobuf pointer. Leaves additional data in the copy buffer.
 */
static void efx_memcpy_toio_aligned_cb(struct efx_nic *efx, u8 __iomem **piobuf,
                                       u8 *data, int len,
                                       struct efx_short_copy_buffer *copy_buf)
{
        if (copy_buf->used) {
                /* if the copy buffer is partially full, fill it up and write */
                int copy_to_buf =
                        min_t(int, sizeof(copy_buf->buf) - copy_buf->used, len);

                memcpy(copy_buf->buf + copy_buf->used, data, copy_to_buf);
                copy_buf->used += copy_to_buf;

                /* if we didn't fill it up then we're done for now */
                if (copy_buf->used < sizeof(copy_buf->buf))
                        return;

                memcpy_toio(*piobuf, copy_buf->buf, sizeof(copy_buf->buf));
                *piobuf += sizeof(copy_buf->buf);
                data += copy_to_buf;
                len -= copy_to_buf;
                copy_buf->used = 0;
        }

        efx_memcpy_toio_aligned(efx, piobuf, data, len, copy_buf);
}

static void efx_flush_copy_buffer(struct efx_nic *efx, u8 __iomem *piobuf,
                                  struct efx_short_copy_buffer *copy_buf)
{
        /* if there's anything in it, write the whole buffer, including junk */
        if (copy_buf->used)
                memcpy_toio(piobuf, copy_buf->buf, sizeof(copy_buf->buf));
}

/* Traverse skb structure and copy fragments in to PIO buffer.
 * Advances piobuf pointer.
 */
static void efx_skb_copy_bits_to_pio(struct efx_nic *efx, struct sk_buff *skb,
                                     u8 __iomem **piobuf,
                                     struct efx_short_copy_buffer *copy_buf)
{
        int i;

        efx_memcpy_toio_aligned(efx, piobuf, skb->data, skb_headlen(skb),
                                copy_buf);

        for (i = 0; i < skb_shinfo(skb)->nr_frags; ++i) {
                skb_frag_t *f = &skb_shinfo(skb)->frags[i];
                u8 *vaddr;

                vaddr = kmap_atomic(skb_frag_page(f));

                efx_memcpy_toio_aligned_cb(efx, piobuf, vaddr + f->page_offset,
                                           skb_frag_size(f), copy_buf);
                kunmap_atomic(vaddr);
        }

        EFX_BUG_ON_PARANOID(skb_shinfo(skb)->frag_list);
}

static struct efx_tx_buffer *
efx_enqueue_skb_pio(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
{
        struct efx_tx_buffer *buffer =
                efx_tx_queue_get_insert_buffer(tx_queue);
        u8 __iomem *piobuf = tx_queue->piobuf;

        /* Copy to PIO buffer. Ensure the writes are padded to the end
         * of a cache line, as this is required for write-combining to be
         * effective on at least x86.
         */

        if (skb_shinfo(skb)->nr_frags) {
                /* The size of the copy buffer will ensure all writes
                 * are the size of a cache line.
                 */
                struct efx_short_copy_buffer copy_buf;

                copy_buf.used = 0;

                efx_skb_copy_bits_to_pio(tx_queue->efx, skb,
                                         &piobuf, &copy_buf);
                efx_flush_copy_buffer(tx_queue->efx, piobuf, &copy_buf);
        } else {
                /* Pad the write to the size of a cache line.
                 * We can do this because we know the skb_shared_info sruct is
                 * after the source, and the destination buffer is big enough.
                 */
                BUILD_BUG_ON(L1_CACHE_BYTES >
                             SKB_DATA_ALIGN(sizeof(struct skb_shared_info)));
                memcpy_toio(tx_queue->piobuf, skb->data,
                            ALIGN(skb->len, L1_CACHE_BYTES));
        }

        EFX_POPULATE_QWORD_5(buffer->option,
                             ESF_DZ_TX_DESC_IS_OPT, 1,
                             ESF_DZ_TX_OPTION_TYPE, ESE_DZ_TX_OPTION_DESC_PIO,
                             ESF_DZ_TX_PIO_CONT, 0,
                             ESF_DZ_TX_PIO_BYTE_CNT, skb->len,
                             ESF_DZ_TX_PIO_BUF_ADDR,
                             tx_queue->piobuf_offset);
        ++tx_queue->pio_packets;
        ++tx_queue->insert_count;
        return buffer;
}
#endif /* EFX_USE_PIO */

/*
 * 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.
 *
 * This function is split out from efx_hard_start_xmit to allow the
 * loopback test to direct packets via specific TX queues.
 *
 * Returns NETDEV_TX_OK.
 * You must hold netif_tx_lock() to call this function.
 */
netdev_tx_t efx_enqueue_skb(struct efx_tx_queue *tx_queue, struct sk_buff *skb)
{
        struct efx_nic *efx = tx_queue->efx;
        struct device *dma_dev = &efx->pci_dev->dev;
        struct efx_tx_buffer *buffer;
        skb_frag_t *fragment;
        unsigned int len, unmap_len = 0;
        dma_addr_t dma_addr, unmap_addr = 0;
        unsigned int dma_len;
        unsigned short dma_flags;
        int i = 0;

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

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

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

        /* Pad if necessary */
        if (EFX_WORKAROUND_15592(efx) && skb->len <= 32) {
                EFX_BUG_ON_PARANOID(skb->data_len);
                len = 32 + 1;
                if (skb_pad(skb, len - skb->len))
                        return NETDEV_TX_OK;
        }

        /* Consider using PIO for short packets */
#ifdef EFX_USE_PIO
        if (skb->len <= efx_piobuf_size && tx_queue->piobuf &&
            efx_nic_tx_is_empty(tx_queue) &&
            efx_nic_tx_is_empty(efx_tx_queue_partner(tx_queue))) {
                buffer = efx_enqueue_skb_pio(tx_queue, skb);
                dma_flags = EFX_TX_BUF_OPTION;
                goto finish_packet;
        }
#endif

        /* Map for DMA.  Use dma_map_single rather than dma_map_page
         * since this is more efficient on machines with sparse
         * memory.
         */
        dma_flags = EFX_TX_BUF_MAP_SINGLE;
        dma_addr = dma_map_single(dma_dev, skb->data, len, PCI_DMA_TODEVICE);

        /* Process all fragments */
        while (1) {
                if (unlikely(dma_mapping_error(dma_dev, dma_addr)))
                        goto dma_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 {
                        buffer = efx_tx_queue_get_insert_buffer(tx_queue);

                        dma_len = efx_max_tx_len(efx, dma_addr);
                        if (likely(dma_len >= len))
                                dma_len = len;

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

                /* Transfer ownership of the unmapping to the final buffer */
                buffer->flags = EFX_TX_BUF_CONT | dma_flags;
                buffer->unmap_len = unmap_len;
                buffer->dma_offset = buffer->dma_addr - unmap_addr;
                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 = skb_frag_size(fragment);
                i++;
                /* Map for DMA */
                dma_flags = 0;
                dma_addr = skb_frag_dma_map(dma_dev, fragment, 0, len,
                                            DMA_TO_DEVICE);
        }

        /* Transfer ownership of the skb to the final buffer */
#ifdef EFX_USE_PIO
finish_packet:
#endif
        buffer->skb = skb;
        buffer->flags = EFX_TX_BUF_SKB | dma_flags;

        netdev_tx_sent_queue(tx_queue->core_txq, skb->len);

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

        efx_tx_maybe_stop_queue(tx_queue);

        return NETDEV_TX_OK;

 dma_err:
        netif_err(efx, tx_err, efx->net_dev,
                  " 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(skb);

        /* Work backwards until we hit the original insert pointer value */
        while (tx_queue->insert_count != tx_queue->write_count) {
                unsigned int pkts_compl = 0, bytes_compl = 0;
                --tx_queue->insert_count;
                buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
                efx_dequeue_buffer(tx_queue, buffer, &pkts_compl, &bytes_compl);
        }

        /* Free the fragment we were mid-way through pushing */
        if (unmap_len) {
                if (dma_flags & EFX_TX_BUF_MAP_SINGLE)
                        dma_unmap_single(dma_dev, unmap_addr, unmap_len,
                                         DMA_TO_DEVICE);
                else
                        dma_unmap_page(dma_dev, unmap_addr, unmap_len,
                                       DMA_TO_DEVICE);
        }

        return NETDEV_TX_OK;
}

/* 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,
                                unsigned int *pkts_compl,
                                unsigned int *bytes_compl)
{
        struct efx_nic *efx = tx_queue->efx;
        unsigned int stop_index, read_ptr;

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

        while (read_ptr != stop_index) {
                struct efx_tx_buffer *buffer = &tx_queue->buffer[read_ptr];

                if (!(buffer->flags & EFX_TX_BUF_OPTION) &&
                    unlikely(buffer->len == 0)) {
                        netif_err(efx, tx_err, efx->net_dev,
                                  "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, pkts_compl, bytes_compl);

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

/* 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.
 */
netdev_tx_t 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;
        unsigned index, type;

        EFX_WARN_ON_PARANOID(!netif_device_present(net_dev));

        /* PTP "event" packet */
        if (unlikely(efx_xmit_with_hwtstamp(skb)) &&
            unlikely(efx_ptp_is_ptp_tx(efx, skb))) {
                return efx_ptp_tx(efx, skb);
        }

        index = skb_get_queue_mapping(skb);
        type = skb->ip_summed == CHECKSUM_PARTIAL ? EFX_TXQ_TYPE_OFFLOAD : 0;
        if (index >= efx->n_tx_channels) {
                index -= efx->n_tx_channels;
                type |= EFX_TXQ_TYPE_HIGHPRI;
        }
        tx_queue = efx_get_tx_queue(efx, index, type);

        return efx_enqueue_skb(tx_queue, skb);
}

void efx_init_tx_queue_core_txq(struct efx_tx_queue *tx_queue)
{
        struct efx_nic *efx = tx_queue->efx;

        /* Must be inverse of queue lookup in efx_hard_start_xmit() */
        tx_queue->core_txq =
                netdev_get_tx_queue(efx->net_dev,
                                    tx_queue->queue / EFX_TXQ_TYPES +
                                    ((tx_queue->queue & EFX_TXQ_TYPE_HIGHPRI) ?
                                     efx->n_tx_channels : 0));
}

int efx_setup_tc(struct net_device *net_dev, u8 num_tc)
{
        struct efx_nic *efx = netdev_priv(net_dev);
        struct efx_channel *channel;
        struct efx_tx_queue *tx_queue;
        unsigned tc;
        int rc;

        if (efx_nic_rev(efx) < EFX_REV_FALCON_B0 || num_tc > EFX_MAX_TX_TC)
                return -EINVAL;

        if (num_tc == net_dev->num_tc)
                return 0;

        for (tc = 0; tc < num_tc; tc++) {
                net_dev->tc_to_txq[tc].offset = tc * efx->n_tx_channels;
                net_dev->tc_to_txq[tc].count = efx->n_tx_channels;
        }

        if (num_tc > net_dev->num_tc) {
                /* Initialise high-priority queues as necessary */
                efx_for_each_channel(channel, efx) {
                        efx_for_each_possible_channel_tx_queue(tx_queue,
                                                               channel) {
                                if (!(tx_queue->queue & EFX_TXQ_TYPE_HIGHPRI))
                                        continue;
                                if (!tx_queue->buffer) {
                                        rc = efx_probe_tx_queue(tx_queue);
                                        if (rc)
                                                return rc;
                                }
                                if (!tx_queue->initialised)
                                        efx_init_tx_queue(tx_queue);
                                efx_init_tx_queue_core_txq(tx_queue);
                        }
                }
        } else {
                /* Reduce number of classes before number of queues */
                net_dev->num_tc = num_tc;
        }

        rc = netif_set_real_num_tx_queues(net_dev,
                                          max_t(int, num_tc, 1) *
                                          efx->n_tx_channels);
        if (rc)
                return rc;

        /* Do not destroy high-priority queues when they become
         * unused.  We would have to flush them first, and it is
         * fairly difficult to flush a subset of TX queues.  Leave
         * it to efx_fini_channels().
         */

        net_dev->num_tc = num_tc;
        return 0;
}

void efx_xmit_done(struct efx_tx_queue *tx_queue, unsigned int index)
{
        unsigned fill_level;
        struct efx_nic *efx = tx_queue->efx;
        struct efx_tx_queue *txq2;
        unsigned int pkts_compl = 0, bytes_compl = 0;

        EFX_BUG_ON_PARANOID(index > tx_queue->ptr_mask);

        efx_dequeue_buffers(tx_queue, index, &pkts_compl, &bytes_compl);
        netdev_tx_completed_queue(tx_queue->core_txq, pkts_compl, bytes_compl);

        if (pkts_compl > 1)
                ++tx_queue->merge_events;

        /* See if we need to restart the netif queue.  This memory
         * barrier ensures that we write read_count (inside
         * efx_dequeue_buffers()) before reading the queue status.
         */
        smp_mb();
        if (unlikely(netif_tx_queue_stopped(tx_queue->core_txq)) &&
            likely(efx->port_enabled) &&
            likely(netif_device_present(efx->net_dev))) {
                txq2 = efx_tx_queue_partner(tx_queue);
                fill_level = max(tx_queue->insert_count - tx_queue->read_count,
                                 txq2->insert_count - txq2->read_count);
                if (fill_level <= efx->txq_wake_thresh)
                        netif_tx_wake_queue(tx_queue->core_txq);
        }

        /* Check whether the hardware queue is now empty */
        if ((int)(tx_queue->read_count - tx_queue->old_write_count) >= 0) {
                tx_queue->old_write_count = ACCESS_ONCE(tx_queue->write_count);
                if (tx_queue->read_count == tx_queue->old_write_count) {
                        smp_mb();
                        tx_queue->empty_read_count =
                                tx_queue->read_count | EFX_EMPTY_COUNT_VALID;
                }
        }
}

/* Size of page-based TSO header buffers.  Larger blocks must be
 * allocated from the heap.
 */
#define TSOH_STD_SIZE   128
#define TSOH_PER_PAGE   (PAGE_SIZE / TSOH_STD_SIZE)

/* At most half the descriptors in the queue at any time will refer to
 * a TSO header buffer, since they must always be followed by a
 * payload descriptor referring to an skb.
 */
static unsigned int efx_tsoh_page_count(struct efx_tx_queue *tx_queue)
{
        return DIV_ROUND_UP(tx_queue->ptr_mask + 1, 2 * TSOH_PER_PAGE);
}

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

        /* Create the smallest power-of-two aligned ring */
        entries = max(roundup_pow_of_two(efx->txq_entries), EFX_MIN_DMAQ_SIZE);
        EFX_BUG_ON_PARANOID(entries > EFX_MAX_DMAQ_SIZE);
        tx_queue->ptr_mask = entries - 1;

        netif_dbg(efx, probe, efx->net_dev,
                  "creating TX queue %d size %#x mask %#x\n",
                  tx_queue->queue, efx->txq_entries, tx_queue->ptr_mask);

        /* Allocate software ring */
        tx_queue->buffer = kcalloc(entries, sizeof(*tx_queue->buffer),
                                   GFP_KERNEL);
        if (!tx_queue->buffer)
                return -ENOMEM;

        if (tx_queue->queue & EFX_TXQ_TYPE_OFFLOAD) {
                tx_queue->tsoh_page =
                        kcalloc(efx_tsoh_page_count(tx_queue),
                                sizeof(tx_queue->tsoh_page[0]), GFP_KERNEL);
                if (!tx_queue->tsoh_page) {
                        rc = -ENOMEM;
                        goto fail1;
                }
        }

        /* Allocate hardware ring */
        rc = efx_nic_probe_tx(tx_queue);
        if (rc)
                goto fail2;

        return 0;

fail2:
        kfree(tx_queue->tsoh_page);
        tx_queue->tsoh_page = NULL;
fail1:
        kfree(tx_queue->buffer);
        tx_queue->buffer = NULL;
        return rc;
}

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

        tx_queue->insert_count = 0;
        tx_queue->write_count = 0;
        tx_queue->old_write_count = 0;
        tx_queue->read_count = 0;
        tx_queue->old_read_count = 0;
        tx_queue->empty_read_count = 0 | EFX_EMPTY_COUNT_VALID;

        /* Set up TX descriptor ring */
        efx_nic_init_tx(tx_queue);

        tx_queue->initialised = true;
}

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

        netif_dbg(tx_queue->efx, drv, tx_queue->efx->net_dev,
                  "shutting down TX queue %d\n", tx_queue->queue);

        if (!tx_queue->buffer)
                return;

        /* Free any buffers left in the ring */
        while (tx_queue->read_count != tx_queue->write_count) {
                unsigned int pkts_compl = 0, bytes_compl = 0;
                buffer = &tx_queue->buffer[tx_queue->read_count & tx_queue->ptr_mask];
                efx_dequeue_buffer(tx_queue, buffer, &pkts_compl, &bytes_compl);

                ++tx_queue->read_count;
        }
        netdev_tx_reset_queue(tx_queue->core_txq);
}

void efx_remove_tx_queue(struct efx_tx_queue *tx_queue)
{
        int i;

        if (!tx_queue->buffer)
                return;

        netif_dbg(tx_queue->efx, drv, tx_queue->efx->net_dev,
                  "destroying TX queue %d\n", tx_queue->queue);
        efx_nic_remove_tx(tx_queue);

        if (tx_queue->tsoh_page) {
                for (i = 0; i < efx_tsoh_page_count(tx_queue); i++)
                        efx_nic_free_buffer(tx_queue->efx,
                                            &tx_queue->tsoh_page[i]);
                kfree(tx_queue->tsoh_page);
                tx_queue->tsoh_page = NULL;
        }

        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 PTR_DIFF(p1, p2)  ((u8 *)(p1) - (u8 *)(p2))

/**
 * 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
 * @dma_flags: TX buffer flags for DMA mapping - %EFX_TX_BUF_MAP_SINGLE or 0
 * @protocol: Network protocol (after any VLAN header)
 * @ip_off: Offset of IP header
 * @tcp_off: Offset of TCP header
 * @header_len: Number of bytes of header
 * @ip_base_len: IPv4 tot_len or IPv6 payload_len, before TCP payload
 * @header_dma_addr: Header DMA address, when using option descriptors
 * @header_unmap_len: Header DMA mapped length, or 0 if not using option
 *      descriptors
 *
 * 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;
        u16 ipv4_id;
        unsigned packet_space;

        /* Input position */
        dma_addr_t dma_addr;
        unsigned in_len;
        unsigned unmap_len;
        dma_addr_t unmap_addr;
        unsigned short dma_flags;

        __be16 protocol;
        unsigned int ip_off;
        unsigned int tcp_off;
        unsigned header_len;
        unsigned int ip_base_len;
        dma_addr_t header_dma_addr;
        unsigned int header_unmap_len;
};


/*
 * Verify that our various assumptions about sk_buffs and the conditions
 * under which TSO will be attempted hold true.  Return the protocol number.
 */
static __be16 efx_tso_check_protocol(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)) {
                struct vlan_ethhdr *veh = (struct vlan_ethhdr *)skb->data;
                protocol = veh->h_vlan_encapsulated_proto;
        }

        if (protocol == htons(ETH_P_IP)) {
                EFX_BUG_ON_PARANOID(ip_hdr(skb)->protocol != IPPROTO_TCP);
        } else {
                EFX_BUG_ON_PARANOID(protocol != htons(ETH_P_IPV6));
                EFX_BUG_ON_PARANOID(ipv6_hdr(skb)->nexthdr != NEXTHDR_TCP);
        }
        EFX_BUG_ON_PARANOID((PTR_DIFF(tcp_hdr(skb), skb->data)
                             + (tcp_hdr(skb)->doff << 2u)) >
                            skb_headlen(skb));

        return protocol;
}

static u8 *efx_tsoh_get_buffer(struct efx_tx_queue *tx_queue,
                               struct efx_tx_buffer *buffer, unsigned int len)
{
        u8 *result;

        EFX_BUG_ON_PARANOID(buffer->len);
        EFX_BUG_ON_PARANOID(buffer->flags);
        EFX_BUG_ON_PARANOID(buffer->unmap_len);

        if (likely(len <= TSOH_STD_SIZE - TSOH_OFFSET)) {
                unsigned index =
                        (tx_queue->insert_count & tx_queue->ptr_mask) / 2;
                struct efx_buffer *page_buf =
                        &tx_queue->tsoh_page[index / TSOH_PER_PAGE];
                unsigned offset =
                        TSOH_STD_SIZE * (index % TSOH_PER_PAGE) + TSOH_OFFSET;

                if (unlikely(!page_buf->addr) &&
                    efx_nic_alloc_buffer(tx_queue->efx, page_buf, PAGE_SIZE,
                                         GFP_ATOMIC))
                        return NULL;

                result = (u8 *)page_buf->addr + offset;
                buffer->dma_addr = page_buf->dma_addr + offset;
                buffer->flags = EFX_TX_BUF_CONT;
        } else {
                tx_queue->tso_long_headers++;

                buffer->heap_buf = kmalloc(TSOH_OFFSET + len, GFP_ATOMIC);
                if (unlikely(!buffer->heap_buf))
                        return NULL;
                result = (u8 *)buffer->heap_buf + TSOH_OFFSET;
                buffer->flags = EFX_TX_BUF_CONT | EFX_TX_BUF_HEAP;
        }

        buffer->len = len;

        return result;
}

/**
 * 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.
 */
static void 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;

        EFX_BUG_ON_PARANOID(len <= 0);

        while (1) {
                buffer = efx_tx_queue_get_insert_buffer(tx_queue);
                ++tx_queue->insert_count;

                EFX_BUG_ON_PARANOID(tx_queue->insert_count -
                                    tx_queue->read_count >=
                                    efx->txq_entries);

                buffer->dma_addr = dma_addr;

                dma_len = efx_max_tx_len(efx, dma_addr);

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

                buffer->len = dma_len;
                buffer->flags = EFX_TX_BUF_CONT;
                dma_addr += dma_len;
                len -= dma_len;
        }

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


/*
 * 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 int efx_tso_put_header(struct efx_tx_queue *tx_queue,
                              struct efx_tx_buffer *buffer, u8 *header)
{
        if (unlikely(buffer->flags & EFX_TX_BUF_HEAP)) {
                buffer->dma_addr = dma_map_single(&tx_queue->efx->pci_dev->dev,
                                                  header, buffer->len,
                                                  DMA_TO_DEVICE);
                if (unlikely(dma_mapping_error(&tx_queue->efx->pci_dev->dev,
                                               buffer->dma_addr))) {
                        kfree(buffer->heap_buf);
                        buffer->len = 0;
                        buffer->flags = 0;
                        return -ENOMEM;
                }
                buffer->unmap_len = buffer->len;
                buffer->dma_offset = 0;
                buffer->flags |= EFX_TX_BUF_MAP_SINGLE;
        }

        ++tx_queue->insert_count;
        return 0;
}


/* Remove buffers put into a tx_queue.  None of the buffers must have
 * an skb attached.
 */
static void efx_enqueue_unwind(struct efx_tx_queue *tx_queue)
{
        struct efx_tx_buffer *buffer;

        /* Work backwards until we hit the original insert pointer value */
        while (tx_queue->insert_count != tx_queue->write_count) {
                --tx_queue->insert_count;
                buffer = __efx_tx_queue_get_insert_buffer(tx_queue);
                efx_dequeue_buffer(tx_queue, buffer, NULL, NULL);
        }
}


/* Parse the SKB header and initialise state. */
static int tso_start(struct tso_state *st, struct efx_nic *efx,
                     const struct sk_buff *skb)
{
        bool use_options = efx_nic_rev(efx) >= EFX_REV_HUNT_A0;
        struct device *dma_dev = &efx->pci_dev->dev;
        unsigned int header_len, in_len;
        dma_addr_t dma_addr;

        st->ip_off = skb_network_header(skb) - skb->data;
        st->tcp_off = skb_transport_header(skb) - skb->data;
        header_len = st->tcp_off + (tcp_hdr(skb)->doff << 2u);
        in_len = skb_headlen(skb) - header_len;
        st->header_len = header_len;
        st->in_len = in_len;
        if (st->protocol == htons(ETH_P_IP)) {
                st->ip_base_len = st->header_len - st->ip_off;
                st->ipv4_id = ntohs(ip_hdr(skb)->id);
        } else {
                st->ip_base_len = st->header_len - st->tcp_off;
                st->ipv4_id = 0;
        }
        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->out_len = skb->len - header_len;

        if (!use_options) {
                st->header_unmap_len = 0;

                if (likely(in_len == 0)) {
                        st->dma_flags = 0;
                        st->unmap_len = 0;
                        return 0;
                }

                dma_addr = dma_map_single(dma_dev, skb->data + header_len,
                                          in_len, DMA_TO_DEVICE);
                st->dma_flags = EFX_TX_BUF_MAP_SINGLE;
                st->dma_addr = dma_addr;
                st->unmap_addr = dma_addr;
                st->unmap_len = in_len;
        } else {
                dma_addr = dma_map_single(dma_dev, skb->data,
                                          skb_headlen(skb), DMA_TO_DEVICE);
                st->header_dma_addr = dma_addr;
                st->header_unmap_len = skb_headlen(skb);
                st->dma_flags = 0;
                st->dma_addr = dma_addr + header_len;
                st->unmap_len = 0;
        }

        return unlikely(dma_mapping_error(dma_dev, dma_addr)) ? -ENOMEM : 0;
}

static int tso_get_fragment(struct tso_state *st, struct efx_nic *efx,
                            skb_frag_t *frag)
{
        st->unmap_addr = skb_frag_dma_map(&efx->pci_dev->dev, frag, 0,
                                          skb_frag_size(frag), DMA_TO_DEVICE);
        if (likely(!dma_mapping_error(&efx->pci_dev->dev, st->unmap_addr))) {
                st->dma_flags = 0;
                st->unmap_len = skb_frag_size(frag);
                st->in_len = skb_frag_size(frag);
                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.
 */
static void 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;

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

        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;

        efx_tx_queue_insert(tx_queue, st->dma_addr, n, &buffer);

        if (st->out_len == 0) {
                /* Transfer ownership of the skb */
                buffer->skb = skb;
                buffer->flags = EFX_TX_BUF_SKB;
        } else if (st->packet_space != 0) {
                buffer->flags = EFX_TX_BUF_CONT;
        }

        if (st->in_len == 0) {
                /* Transfer ownership of the DMA mapping */
                buffer->unmap_len = st->unmap_len;
                buffer->dma_offset = buffer->unmap_len - buffer->len;
                buffer->flags |= st->dma_flags;
                st->unmap_len = 0;
        }

        st->dma_addr += n;
}


/**
 * 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 -%ENOMEM 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_tx_buffer *buffer =
                efx_tx_queue_get_insert_buffer(tx_queue);
        bool is_last = st->out_len <= skb_shinfo(skb)->gso_size;
        u8 tcp_flags_clear;

        if (!is_last) {
                st->packet_space = skb_shinfo(skb)->gso_size;
                tcp_flags_clear = 0x09; /* mask out FIN and PSH */
        } else {
                st->packet_space = st->out_len;
                tcp_flags_clear = 0x00;
        }

        if (!st->header_unmap_len) {
                /* Allocate and insert a DMA-mapped header buffer. */
                struct tcphdr *tsoh_th;
                unsigned ip_length;
                u8 *header;
                int rc;

                header = efx_tsoh_get_buffer(tx_queue, buffer, st->header_len);
                if (!header)
                        return -ENOMEM;

                tsoh_th = (struct tcphdr *)(header + st->tcp_off);

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

                tsoh_th->seq = htonl(st->seqnum);
                ((u8 *)tsoh_th)[13] &= ~tcp_flags_clear;

                ip_length = st->ip_base_len + st->packet_space;

                if (st->protocol == htons(ETH_P_IP)) {
                        struct iphdr *tsoh_iph =
                                (struct iphdr *)(header + st->ip_off);

                        tsoh_iph->tot_len = htons(ip_length);
                        tsoh_iph->id = htons(st->ipv4_id);
                } else {
                        struct ipv6hdr *tsoh_iph =
                                (struct ipv6hdr *)(header + st->ip_off);

                        tsoh_iph->payload_len = htons(ip_length);
                }

                rc = efx_tso_put_header(tx_queue, buffer, header);
                if (unlikely(rc))
                        return rc;
        } else {
                /* Send the original headers with a TSO option descriptor
                 * in front
                 */
                u8 tcp_flags = ((u8 *)tcp_hdr(skb))[13] & ~tcp_flags_clear;

                buffer->flags = EFX_TX_BUF_OPTION;
                buffer->len = 0;
                buffer->unmap_len = 0;
                EFX_POPULATE_QWORD_5(buffer->option,
                                     ESF_DZ_TX_DESC_IS_OPT, 1,
                                     ESF_DZ_TX_OPTION_TYPE,
                                     ESE_DZ_TX_OPTION_DESC_TSO,
                                     ESF_DZ_TX_TSO_TCP_FLAGS, tcp_flags,
                                     ESF_DZ_TX_TSO_IP_ID, st->ipv4_id,
                                     ESF_DZ_TX_TSO_TCP_SEQNO, st->seqnum);
                ++tx_queue->insert_count;

                /* We mapped the headers in tso_start().  Unmap them
                 * when the last segment is completed.
                 */
                buffer = efx_tx_queue_get_insert_buffer(tx_queue);
                buffer->dma_addr = st->header_dma_addr;
                buffer->len = st->header_len;
                if (is_last) {
                        buffer->flags = EFX_TX_BUF_CONT | EFX_TX_BUF_MAP_SINGLE;
                        buffer->unmap_len = st->header_unmap_len;
                        buffer->dma_offset = 0;
                        /* Ensure we only unmap them once in case of a
                         * later DMA mapping error and rollback
                         */
                        st->header_unmap_len = 0;
                } else {
                        buffer->flags = EFX_TX_BUF_CONT;
                        buffer->unmap_len = 0;
                }
                ++tx_queue->insert_count;
        }

        st->seqnum += skb_shinfo(skb)->gso_size;

        /* Linux leaves suitable gaps in the IP ID space for us to fill. */
        ++st->ipv4_id;

        ++tx_queue->tso_packets;

        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.
 */
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;
        struct tso_state state;

        /* Find the packet protocol and sanity-check it */
        state.protocol = efx_tso_check_protocol(skb);

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

        rc = tso_start(&state, efx, skb);
        if (rc)
                goto mem_err;

        if (likely(state.in_len == 0)) {
                /* 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 {
                /* Payload starts in the header area. */
                frag_i = -1;
        }

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

        while (1) {
                tso_fill_packet_with_fragment(tx_queue, skb, &state);

                /* 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;
        }

        netdev_tx_sent_queue(tx_queue->core_txq, skb->len);

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

        efx_tx_maybe_stop_queue(tx_queue);

        tx_queue->tso_bursts++;
        return NETDEV_TX_OK;

 mem_err:
        netif_err(efx, tx_err, efx->net_dev,
                  "Out of memory for TSO headers, or DMA mapping error\n");
        dev_kfree_skb_any(skb);

        /* Free the DMA mapping we were in the process of writing out */
        if (state.unmap_len) {
                if (state.dma_flags & EFX_TX_BUF_MAP_SINGLE)
                        dma_unmap_single(&efx->pci_dev->dev, state.unmap_addr,
                                         state.unmap_len, DMA_TO_DEVICE);
                else
                        dma_unmap_page(&efx->pci_dev->dev, state.unmap_addr,
                                       state.unmap_len, DMA_TO_DEVICE);
        }

        /* Free the header DMA mapping, if using option descriptors */
        if (state.header_unmap_len)
                dma_unmap_single(&efx->pci_dev->dev, state.header_dma_addr,
                                 state.header_unmap_len, DMA_TO_DEVICE);

        efx_enqueue_unwind(tx_queue);
        return NETDEV_TX_OK;
}