rx.c

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/****************************************************************************
 * Driver for Solarflare Solarstorm network controllers and boards
 * Copyright 2005-2006 Fen Systems Ltd.
 * Copyright 2005-2011 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/socket.h>
#include <linux/in.h>
#include <linux/slab.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/prefetch.h>
#include <linux/moduleparam.h>
#include <net/ip.h>
#include <net/checksum.h>
#include "net_driver.h"
#include "efx.h"
#include "nic.h"
#include "selftest.h"
#include "workarounds.h"

/* Number of RX descriptors pushed at once. */
#define EFX_RX_BATCH  8

/* Maximum size of a buffer sharing a page */
#define EFX_RX_HALF_PAGE ((PAGE_SIZE >> 1) - sizeof(struct efx_rx_page_state))

/* Size of buffer allocated for skb header area. */
#define EFX_SKB_HEADERS  64u

/*
 * rx_alloc_method - RX buffer allocation method
 *
 * This driver supports two methods for allocating and using RX buffers:
 * each RX buffer may be backed by an skb or by an order-n page.
 *
 * When GRO is in use then the second method has a lower overhead,
 * since we don't have to allocate then free skbs on reassembled frames.
 *
 * Values:
 *   - RX_ALLOC_METHOD_AUTO = 0
 *   - RX_ALLOC_METHOD_SKB  = 1
 *   - RX_ALLOC_METHOD_PAGE = 2
 *
 * The heuristic for %RX_ALLOC_METHOD_AUTO is a simple hysteresis count
 * controlled by the parameters below.
 *
 *   - Since pushing and popping descriptors are separated by the rx_queue
 *     size, so the watermarks should be ~rxd_size.
 *   - The performance win by using page-based allocation for GRO is less
 *     than the performance hit of using page-based allocation of non-GRO,
 *     so the watermarks should reflect this.
 *
 * Per channel we maintain a single variable, updated by each channel:
 *
 *   rx_alloc_level += (gro_performed ? RX_ALLOC_FACTOR_GRO :
 *                      RX_ALLOC_FACTOR_SKB)
 * Per NAPI poll interval, we constrain rx_alloc_level to 0..MAX (which
 * limits the hysteresis), and update the allocation strategy:
 *
 *   rx_alloc_method = (rx_alloc_level > RX_ALLOC_LEVEL_GRO ?
 *                      RX_ALLOC_METHOD_PAGE : RX_ALLOC_METHOD_SKB)
 */
static int rx_alloc_method = RX_ALLOC_METHOD_AUTO;

#define RX_ALLOC_LEVEL_GRO 0x2000
#define RX_ALLOC_LEVEL_MAX 0x3000
#define RX_ALLOC_FACTOR_GRO 1
#define RX_ALLOC_FACTOR_SKB (-2)

/* This is the percentage fill level below which new RX descriptors
 * will be added to the RX descriptor ring.
 */
static unsigned int rx_refill_threshold;

/*
 * RX maximum head room required.
 *
 * This must be at least 1 to prevent overflow and at least 2 to allow
 * pipelined receives.
 */
#define EFX_RXD_HEAD_ROOM 2

/* Offset of ethernet header within page */
static inline unsigned int efx_rx_buf_offset(struct efx_nic *efx,
                         struct efx_rx_buffer *buf)
{
    /* Offset is always within one page, so we don't need to consider
     * the page order.
     */
    return ((unsigned int) buf->dma_addr & (PAGE_SIZE - 1)) +
        efx->type->rx_buffer_hash_size;
}
static inline unsigned int efx_rx_buf_size(struct efx_nic *efx)
{
    return PAGE_SIZE << efx->rx_buffer_order;
}

static u8 *efx_rx_buf_eh(struct efx_nic *efx, struct efx_rx_buffer *buf)
{
    if (buf->flags & EFX_RX_BUF_PAGE)
        return page_address(buf->u.page) + efx_rx_buf_offset(efx, buf);
    else
        return (u8 *)buf->u.skb->data + efx->type->rx_buffer_hash_size;
}

static inline u32 efx_rx_buf_hash(const u8 *eh)
{
    /* The ethernet header is always directly after any hash. */
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS) || NET_IP_ALIGN % 4 == 0
    return __le32_to_cpup((const __le32 *)(eh - 4));
#else
    const u8 *data = eh - 4;
    return (u32)data[0]   |
           (u32)data[1] << 8  |
           (u32)data[2] << 16 |
           (u32)data[3] << 24;
#endif
}

static int efx_init_rx_buffers_skb(struct efx_rx_queue *rx_queue)
{
    struct efx_nic *efx = rx_queue->efx;
    struct net_device *net_dev = efx->net_dev;
    struct efx_rx_buffer *rx_buf;
    struct sk_buff *skb;
    int skb_len = efx->rx_buffer_len;
    unsigned index, count;

    for (count = 0; count < EFX_RX_BATCH; ++count) {
        index = rx_queue->added_count & rx_queue->ptr_mask;
        rx_buf = efx_rx_buffer(rx_queue, index);

        rx_buf->u.skb = skb = netdev_alloc_skb(net_dev, skb_len);
        if (unlikely(!skb))
            return -ENOMEM;

        /* Adjust the SKB for padding */
        skb_reserve(skb, NET_IP_ALIGN);
        rx_buf->len = skb_len - NET_IP_ALIGN;
        rx_buf->flags = 0;

        rx_buf->dma_addr = dma_map_single(&efx->pci_dev->dev,
                          skb->data, rx_buf->len,
                          DMA_FROM_DEVICE);
        if (unlikely(dma_mapping_error(&efx->pci_dev->dev,
                           rx_buf->dma_addr))) {
            dev_kfree_skb_any(skb);
            rx_buf->u.skb = NULL;
            return -EIO;
        }

        ++rx_queue->added_count;
        ++rx_queue->alloc_skb_count;
    }

    return 0;
}

static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
{
    struct efx_nic *efx = rx_queue->efx;
    struct efx_rx_buffer *rx_buf;
    struct page *page;
    void *page_addr;
    struct efx_rx_page_state *state;
    dma_addr_t dma_addr;
    unsigned index, count;

    /* We can split a page between two buffers */
    BUILD_BUG_ON(EFX_RX_BATCH & 1);

    for (count = 0; count < EFX_RX_BATCH; ++count) {
        page = alloc_pages(__GFP_COLD | __GFP_COMP | GFP_ATOMIC,
                   efx->rx_buffer_order);
        if (unlikely(page == NULL))
            return -ENOMEM;
        dma_addr = dma_map_page(&efx->pci_dev->dev, page, 0,
                    efx_rx_buf_size(efx),
                    DMA_FROM_DEVICE);
        if (unlikely(dma_mapping_error(&efx->pci_dev->dev, dma_addr))) {
            __free_pages(page, efx->rx_buffer_order);
            return -EIO;
        }
        page_addr = page_address(page);
        state = page_addr;
        state->refcnt = 0;
        state->dma_addr = dma_addr;

        page_addr += sizeof(struct efx_rx_page_state);
        dma_addr += sizeof(struct efx_rx_page_state);

    split:
        index = rx_queue->added_count & rx_queue->ptr_mask;
        rx_buf = efx_rx_buffer(rx_queue, index);
        rx_buf->dma_addr = dma_addr + EFX_PAGE_IP_ALIGN;
        rx_buf->u.page = page;
        rx_buf->len = efx->rx_buffer_len - EFX_PAGE_IP_ALIGN;
        rx_buf->flags = EFX_RX_BUF_PAGE;
        ++rx_queue->added_count;
        ++rx_queue->alloc_page_count;
        ++state->refcnt;

        if ((~count & 1) && (efx->rx_buffer_len <= EFX_RX_HALF_PAGE)) {
            /* Use the second half of the page */
            get_page(page);
            dma_addr += (PAGE_SIZE >> 1);
            page_addr += (PAGE_SIZE >> 1);
            ++count;
            goto split;
        }
    }

    return 0;
}

static void efx_unmap_rx_buffer(struct efx_nic *efx,
                struct efx_rx_buffer *rx_buf)
{
    if ((rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.page) {
        struct efx_rx_page_state *state;

        state = page_address(rx_buf->u.page);
        if (--state->refcnt == 0) {
            dma_unmap_page(&efx->pci_dev->dev,
                       state->dma_addr,
                       efx_rx_buf_size(efx),
                       DMA_FROM_DEVICE);
        }
    } else if (!(rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.skb) {
        dma_unmap_single(&efx->pci_dev->dev, rx_buf->dma_addr,
                 rx_buf->len, DMA_FROM_DEVICE);
    }
}

static void efx_free_rx_buffer(struct efx_nic *efx,
                   struct efx_rx_buffer *rx_buf)
{
    if ((rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.page) {
        __free_pages(rx_buf->u.page, efx->rx_buffer_order);
        rx_buf->u.page = NULL;
    } else if (!(rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.skb) {
        dev_kfree_skb_any(rx_buf->u.skb);
        rx_buf->u.skb = NULL;
    }
}

static void efx_fini_rx_buffer(struct efx_rx_queue *rx_queue,
                   struct efx_rx_buffer *rx_buf)
{
    efx_unmap_rx_buffer(rx_queue->efx, rx_buf);
    efx_free_rx_buffer(rx_queue->efx, rx_buf);
}

/* Attempt to resurrect the other receive buffer that used to share this page,
 * which had previously been passed up to the kernel and freed. */
static void efx_resurrect_rx_buffer(struct efx_rx_queue *rx_queue,
                    struct efx_rx_buffer *rx_buf)
{
    struct efx_rx_page_state *state = page_address(rx_buf->u.page);
    struct efx_rx_buffer *new_buf;
    unsigned fill_level, index;

    /* +1 because efx_rx_packet() incremented removed_count. +1 because
     * we'd like to insert an additional descriptor whilst leaving
     * EFX_RXD_HEAD_ROOM for the non-recycle path */
    fill_level = (rx_queue->added_count - rx_queue->removed_count + 2);
    if (unlikely(fill_level > rx_queue->max_fill)) {
        /* We could place "state" on a list, and drain the list in
         * efx_fast_push_rx_descriptors(). For now, this will do. */
        return;
    }

    ++state->refcnt;
    get_page(rx_buf->u.page);

    index = rx_queue->added_count & rx_queue->ptr_mask;
    new_buf = efx_rx_buffer(rx_queue, index);
    new_buf->dma_addr = rx_buf->dma_addr ^ (PAGE_SIZE >> 1);
    new_buf->u.page = rx_buf->u.page;
    new_buf->len = rx_buf->len;
    new_buf->flags = EFX_RX_BUF_PAGE;
    ++rx_queue->added_count;
}

/* Recycle the given rx buffer directly back into the rx_queue. There is
 * always room to add this buffer, because we've just popped a buffer. */
static void efx_recycle_rx_buffer(struct efx_channel *channel,
                  struct efx_rx_buffer *rx_buf)
{
    struct efx_nic *efx = channel->efx;
    struct efx_rx_queue *rx_queue = efx_channel_get_rx_queue(channel);
    struct efx_rx_buffer *new_buf;
    unsigned index;

    rx_buf->flags &= EFX_RX_BUF_PAGE;

    if ((rx_buf->flags & EFX_RX_BUF_PAGE) &&
        efx->rx_buffer_len <= EFX_RX_HALF_PAGE &&
        page_count(rx_buf->u.page) == 1)
        efx_resurrect_rx_buffer(rx_queue, rx_buf);

    index = rx_queue->added_count & rx_queue->ptr_mask;
    new_buf = efx_rx_buffer(rx_queue, index);

    memcpy(new_buf, rx_buf, sizeof(*new_buf));
    rx_buf->u.page = NULL;
    ++rx_queue->added_count;
}

void efx_fast_push_rx_descriptors(struct efx_rx_queue *rx_queue)
{
    struct efx_channel *channel = efx_rx_queue_channel(rx_queue);
    unsigned fill_level;
    int space, rc = 0;

    /* Calculate current fill level, and exit if we don't need to fill */
    fill_level = (rx_queue->added_count - rx_queue->removed_count);
    EFX_BUG_ON_PARANOID(fill_level > rx_queue->efx->rxq_entries);
    if (fill_level >= rx_queue->fast_fill_trigger)
        goto out;

    /* Record minimum fill level */
    if (unlikely(fill_level < rx_queue->min_fill)) {
        if (fill_level)
            rx_queue->min_fill = fill_level;
    }

    space = rx_queue->max_fill - fill_level;
    EFX_BUG_ON_PARANOID(space < EFX_RX_BATCH);

    netif_vdbg(rx_queue->efx, rx_status, rx_queue->efx->net_dev,
           "RX queue %d fast-filling descriptor ring from"
           " level %d to level %d using %s allocation\n",
           efx_rx_queue_index(rx_queue), fill_level,
           rx_queue->max_fill,
           channel->rx_alloc_push_pages ? "page" : "skb");

    do {
        if (channel->rx_alloc_push_pages)
            rc = efx_init_rx_buffers_page(rx_queue);
        else
            rc = efx_init_rx_buffers_skb(rx_queue);
        if (unlikely(rc)) {
            /* Ensure that we don't leave the rx queue empty */
            if (rx_queue->added_count == rx_queue->removed_count)
                efx_schedule_slow_fill(rx_queue);
            goto out;
        }
    } while ((space -= EFX_RX_BATCH) >= EFX_RX_BATCH);

    netif_vdbg(rx_queue->efx, rx_status, rx_queue->efx->net_dev,
           "RX queue %d fast-filled descriptor ring "
           "to level %d\n", efx_rx_queue_index(rx_queue),
           rx_queue->added_count - rx_queue->removed_count);

 out:
    if (rx_queue->notified_count != rx_queue->added_count)
        efx_nic_notify_rx_desc(rx_queue);
}

void efx_rx_slow_fill(unsigned long context)
{
    struct efx_rx_queue *rx_queue = (struct efx_rx_queue *)context;

    /* Post an event to cause NAPI to run and refill the queue */
    efx_nic_generate_fill_event(rx_queue);
    ++rx_queue->slow_fill_count;
}

static void efx_rx_packet__check_len(struct efx_rx_queue *rx_queue,
                     struct efx_rx_buffer *rx_buf,
                     int len, bool *leak_packet)
{
    struct efx_nic *efx = rx_queue->efx;
    unsigned max_len = rx_buf->len - efx->type->rx_buffer_padding;

    if (likely(len <= max_len))
        return;

    /* The packet must be discarded, but this is only a fatal error
     * if the caller indicated it was
     */
    rx_buf->flags |= EFX_RX_PKT_DISCARD;

    if ((len > rx_buf->len) && EFX_WORKAROUND_8071(efx)) {
        if (net_ratelimit())
            netif_err(efx, rx_err, efx->net_dev,
                  " RX queue %d seriously overlength "
                  "RX event (0x%x > 0x%x+0x%x). Leaking\n",
                  efx_rx_queue_index(rx_queue), len, max_len,
                  efx->type->rx_buffer_padding);
        /* If this buffer was skb-allocated, then the meta
         * data at the end of the skb will be trashed. So
         * we have no choice but to leak the fragment.
         */
        *leak_packet = !(rx_buf->flags & EFX_RX_BUF_PAGE);
        efx_schedule_reset(efx, RESET_TYPE_RX_RECOVERY);
    } else {
        if (net_ratelimit())
            netif_err(efx, rx_err, efx->net_dev,
                  " RX queue %d overlength RX event "
                  "(0x%x > 0x%x)\n",
                  efx_rx_queue_index(rx_queue), len, max_len);
    }

    efx_rx_queue_channel(rx_queue)->n_rx_overlength++;
}

/* Pass a received packet up through GRO.  GRO can handle pages
 * regardless of checksum state and skbs with a good checksum.
 */
static void efx_rx_packet_gro(struct efx_channel *channel,
                  struct efx_rx_buffer *rx_buf,
                  const u8 *eh)
{
    struct napi_struct *napi = &channel->napi_str;
    gro_result_t gro_result;

    if (rx_buf->flags & EFX_RX_BUF_PAGE) {
        struct efx_nic *efx = channel->efx;
        struct page *page = rx_buf->u.page;
        struct sk_buff *skb;

        rx_buf->u.page = NULL;

        skb = napi_get_frags(napi);
        if (!skb) {
            put_page(page);
            return;
        }

        if (efx->net_dev->features & NETIF_F_RXHASH)
            skb->rxhash = efx_rx_buf_hash(eh);

        skb_fill_page_desc(skb, 0, page,
                   efx_rx_buf_offset(efx, rx_buf), rx_buf->len);

        skb->len = rx_buf->len;
        skb->data_len = rx_buf->len;
        skb->truesize += rx_buf->len;
        skb->ip_summed = ((rx_buf->flags & EFX_RX_PKT_CSUMMED) ?
                  CHECKSUM_UNNECESSARY : CHECKSUM_NONE);

        skb_record_rx_queue(skb, channel->rx_queue.core_index);

        gro_result = napi_gro_frags(napi);
    } else {
        struct sk_buff *skb = rx_buf->u.skb;

        EFX_BUG_ON_PARANOID(!(rx_buf->flags & EFX_RX_PKT_CSUMMED));
        rx_buf->u.skb = NULL;
        skb->ip_summed = CHECKSUM_UNNECESSARY;

        gro_result = napi_gro_receive(napi, skb);
    }

    if (gro_result == GRO_NORMAL) {
        channel->rx_alloc_level += RX_ALLOC_FACTOR_SKB;
    } else if (gro_result != GRO_DROP) {
        channel->rx_alloc_level += RX_ALLOC_FACTOR_GRO;
        channel->irq_mod_score += 2;
    }
}

void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
           unsigned int len, u16 flags)
{
    struct efx_nic *efx = rx_queue->efx;
    struct efx_channel *channel = efx_rx_queue_channel(rx_queue);
    struct efx_rx_buffer *rx_buf;
    bool leak_packet = false;

    rx_buf = efx_rx_buffer(rx_queue, index);
    rx_buf->flags |= flags;

    /* This allows the refill path to post another buffer.
     * EFX_RXD_HEAD_ROOM ensures that the slot we are using
     * isn't overwritten yet.
     */
    rx_queue->removed_count++;

    /* Validate the length encoded in the event vs the descriptor pushed */
    efx_rx_packet__check_len(rx_queue, rx_buf, len, &leak_packet);

    netif_vdbg(efx, rx_status, efx->net_dev,
           "RX queue %d received id %x at %llx+%x %s%s\n",
           efx_rx_queue_index(rx_queue), index,
           (unsigned long long)rx_buf->dma_addr, len,
           (rx_buf->flags & EFX_RX_PKT_CSUMMED) ? " [SUMMED]" : "",
           (rx_buf->flags & EFX_RX_PKT_DISCARD) ? " [DISCARD]" : "");

    /* Discard packet, if instructed to do so */
    if (unlikely(rx_buf->flags & EFX_RX_PKT_DISCARD)) {
        if (unlikely(leak_packet))
            channel->n_skbuff_leaks++;
        else
            efx_recycle_rx_buffer(channel, rx_buf);

        /* Don't hold off the previous receive */
        rx_buf = NULL;
        goto out;
    }

    /* Release card resources - assumes all RX buffers consumed in-order
     * per RX queue
     */
    efx_unmap_rx_buffer(efx, rx_buf);

    /* Prefetch nice and early so data will (hopefully) be in cache by
     * the time we look at it.
     */
    prefetch(efx_rx_buf_eh(efx, rx_buf));

    /* Pipeline receives so that we give time for packet headers to be
     * prefetched into cache.
     */
    rx_buf->len = len - efx->type->rx_buffer_hash_size;
out:
    if (channel->rx_pkt)
        __efx_rx_packet(channel, channel->rx_pkt);
    channel->rx_pkt = rx_buf;
}

static void efx_rx_deliver(struct efx_channel *channel,
               struct efx_rx_buffer *rx_buf)
{
    struct sk_buff *skb;

    /* We now own the SKB */
    skb = rx_buf->u.skb;
    rx_buf->u.skb = NULL;

    /* Set the SKB flags */
    skb_checksum_none_assert(skb);

    /* Record the rx_queue */
    skb_record_rx_queue(skb, channel->rx_queue.core_index);

    /* Pass the packet up */
    if (channel->type->receive_skb)
        channel->type->receive_skb(channel, skb);
    else
        netif_receive_skb(skb);

    /* Update allocation strategy method */
    channel->rx_alloc_level += RX_ALLOC_FACTOR_SKB;
}

/* Handle a received packet.  Second half: Touches packet payload. */
void __efx_rx_packet(struct efx_channel *channel, struct efx_rx_buffer *rx_buf)
{
    struct efx_nic *efx = channel->efx;
    u8 *eh = efx_rx_buf_eh(efx, rx_buf);

    /* If we're in loopback test, then pass the packet directly to the
     * loopback layer, and free the rx_buf here
     */
    if (unlikely(efx->loopback_selftest)) {
        efx_loopback_rx_packet(efx, eh, rx_buf->len);
        efx_free_rx_buffer(efx, rx_buf);
        return;
    }

    if (!(rx_buf->flags & EFX_RX_BUF_PAGE)) {
        struct sk_buff *skb = rx_buf->u.skb;

        prefetch(skb_shinfo(skb));

        skb_reserve(skb, efx->type->rx_buffer_hash_size);
        skb_put(skb, rx_buf->len);

        if (efx->net_dev->features & NETIF_F_RXHASH)
            skb->rxhash = efx_rx_buf_hash(eh);

        /* Move past the ethernet header. rx_buf->data still points
         * at the ethernet header */
        skb->protocol = eth_type_trans(skb, efx->net_dev);

        skb_record_rx_queue(skb, channel->rx_queue.core_index);
    }

    if (unlikely(!(efx->net_dev->features & NETIF_F_RXCSUM)))
        rx_buf->flags &= ~EFX_RX_PKT_CSUMMED;

    if (likely(rx_buf->flags & (EFX_RX_BUF_PAGE | EFX_RX_PKT_CSUMMED)) &&
        !channel->type->receive_skb)
        efx_rx_packet_gro(channel, rx_buf, eh);
    else
        efx_rx_deliver(channel, rx_buf);
}

void efx_rx_strategy(struct efx_channel *channel)
{
    enum efx_rx_alloc_method method = rx_alloc_method;

    if (channel->type->receive_skb) {
        channel->rx_alloc_push_pages = false;
        return;
    }

    /* Only makes sense to use page based allocation if GRO is enabled */
    if (!(channel->efx->net_dev->features & NETIF_F_GRO)) {
        method = RX_ALLOC_METHOD_SKB;
    } else if (method == RX_ALLOC_METHOD_AUTO) {
        /* Constrain the rx_alloc_level */
        if (channel->rx_alloc_level < 0)
            channel->rx_alloc_level = 0;
        else if (channel->rx_alloc_level > RX_ALLOC_LEVEL_MAX)
            channel->rx_alloc_level = RX_ALLOC_LEVEL_MAX;

        /* Decide on the allocation method */
        method = ((channel->rx_alloc_level > RX_ALLOC_LEVEL_GRO) ?
              RX_ALLOC_METHOD_PAGE : RX_ALLOC_METHOD_SKB);
    }

    /* Push the option */
    channel->rx_alloc_push_pages = (method == RX_ALLOC_METHOD_PAGE);
}

int efx_probe_rx_queue(struct efx_rx_queue *rx_queue)
{
    struct efx_nic *efx = rx_queue->efx;
    unsigned int entries;
    int rc;

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

    netif_dbg(efx, probe, efx->net_dev,
          "creating RX queue %d size %#x mask %#x\n",
          efx_rx_queue_index(rx_queue), efx->rxq_entries,
          rx_queue->ptr_mask);

    /* Allocate RX buffers */
    rx_queue->buffer = kcalloc(entries, sizeof(*rx_queue->buffer),
                   GFP_KERNEL);
    if (!rx_queue->buffer)
        return -ENOMEM;

    rc = efx_nic_probe_rx(rx_queue);
    if (rc) {
        kfree(rx_queue->buffer);
        rx_queue->buffer = NULL;
    }
    return rc;
}

void efx_init_rx_queue(struct efx_rx_queue *rx_queue)
{
    struct efx_nic *efx = rx_queue->efx;
    unsigned int max_fill, trigger, max_trigger;

    netif_dbg(rx_queue->efx, drv, rx_queue->efx->net_dev,
          "initialising RX queue %d\n", efx_rx_queue_index(rx_queue));

    /* Initialise ptr fields */
    rx_queue->added_count = 0;
    rx_queue->notified_count = 0;
    rx_queue->removed_count = 0;
    rx_queue->min_fill = -1U;

    /* Initialise limit fields */
    max_fill = efx->rxq_entries - EFX_RXD_HEAD_ROOM;
    max_trigger = max_fill - EFX_RX_BATCH;
    if (rx_refill_threshold != 0) {
        trigger = max_fill * min(rx_refill_threshold, 100U) / 100U;
        if (trigger > max_trigger)
            trigger = max_trigger;
    } else {
        trigger = max_trigger;
    }

    rx_queue->max_fill = max_fill;
    rx_queue->fast_fill_trigger = trigger;

    /* Set up RX descriptor ring */
    rx_queue->enabled = true;
    efx_nic_init_rx(rx_queue);
}

void efx_fini_rx_queue(struct efx_rx_queue *rx_queue)
{
    int i;
    struct efx_rx_buffer *rx_buf;

    netif_dbg(rx_queue->efx, drv, rx_queue->efx->net_dev,
          "shutting down RX queue %d\n", efx_rx_queue_index(rx_queue));

    /* A flush failure might have left rx_queue->enabled */
    rx_queue->enabled = false;

    del_timer_sync(&rx_queue->slow_fill);
    efx_nic_fini_rx(rx_queue);

    /* Release RX buffers NB start at index 0 not current HW ptr */
    if (rx_queue->buffer) {
        for (i = 0; i <= rx_queue->ptr_mask; i++) {
            rx_buf = efx_rx_buffer(rx_queue, i);
            efx_fini_rx_buffer(rx_queue, rx_buf);
        }
    }
}

void efx_remove_rx_queue(struct efx_rx_queue *rx_queue)
{
    netif_dbg(rx_queue->efx, drv, rx_queue->efx->net_dev,
          "destroying RX queue %d\n", efx_rx_queue_index(rx_queue));

    efx_nic_remove_rx(rx_queue);

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


module_param(rx_alloc_method, int, 0644);
MODULE_PARM_DESC(rx_alloc_method, "Allocation method used for RX buffers");

module_param(rx_refill_threshold, uint, 0444);
MODULE_PARM_DESC(rx_refill_threshold,
         "RX descriptor ring refill threshold (%)");