Linux 3.11-rc3

[cris-mirror.git] / drivers / net / caif / caif_virtio.c

/*
 * Copyright (C) ST-Ericsson AB 2013
 * Authors: Vicram Arv
 *          Dmitry Tarnyagin <dmitry.tarnyagin@lockless.no>
 *          Sjur Brendeland
 * License terms: GNU General Public License (GPL) version 2
 */
#include <linux/module.h>
#include <linux/if_arp.h>
#include <linux/virtio.h>
#include <linux/vringh.h>
#include <linux/debugfs.h>
#include <linux/spinlock.h>
#include <linux/genalloc.h>
#include <linux/interrupt.h>
#include <linux/netdevice.h>
#include <linux/rtnetlink.h>
#include <linux/virtio_ids.h>
#include <linux/virtio_caif.h>
#include <linux/virtio_ring.h>
#include <linux/dma-mapping.h>
#include <net/caif/caif_dev.h>
#include <linux/virtio_config.h>

MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Vicram Arv");
MODULE_AUTHOR("Sjur Brendeland");
MODULE_DESCRIPTION("Virtio CAIF Driver");

/* NAPI schedule quota */
#define CFV_DEFAULT_QUOTA 32

/* Defaults used if virtio config space is unavailable */
#define CFV_DEF_MTU_SIZE 4096
#define CFV_DEF_HEADROOM 32
#define CFV_DEF_TAILROOM 32

/* Required IP header alignment */
#define IP_HDR_ALIGN 4

/* struct cfv_napi_contxt - NAPI context info
 * @riov: IOV holding data read from the ring. Note that riov may
 *        still hold data when cfv_rx_poll() returns.
 * @head: Last descriptor ID we received from vringh_getdesc_kern.
 *        We use this to put descriptor back on the used ring. USHRT_MAX is
 *        used to indicate invalid head-id.
 */
struct cfv_napi_context {
        struct vringh_kiov riov;
        unsigned short head;
};

/* struct cfv_stats - statistics for debugfs
 * @rx_napi_complete:   Number of NAPI completions (RX)
 * @rx_napi_resched:    Number of calls where the full quota was used (RX)
 * @rx_nomem:           Number of SKB alloc failures (RX)
 * @rx_kicks:           Number of RX kicks
 * @tx_full_ring:       Number times TX ring was full
 * @tx_no_mem:          Number of times TX went out of memory
 * @tx_flow_on:         Number of flow on (TX)
 * @tx_kicks:           Number of TX kicks
 */
struct cfv_stats {
        u32 rx_napi_complete;
        u32 rx_napi_resched;
        u32 rx_nomem;
        u32 rx_kicks;
        u32 tx_full_ring;
        u32 tx_no_mem;
        u32 tx_flow_on;
        u32 tx_kicks;
};

/* struct cfv_info - Caif Virtio control structure
 * @cfdev:      caif common header
 * @vdev:       Associated virtio device
 * @vr_rx:      rx/downlink host vring
 * @vq_tx:      tx/uplink virtqueue
 * @ndev:       CAIF link layer device
 * @watermark_tx: indicates number of free descriptors we need
 *              to reopen the tx-queues after overload.
 * @tx_lock:    protects vq_tx from concurrent use
 * @tx_release_tasklet: Tasklet for freeing consumed TX buffers
 * @napi:       Napi context used in cfv_rx_poll()
 * @ctx:        Context data used in cfv_rx_poll()
 * @tx_hr:      transmit headroom
 * @rx_hr:      receive headroom
 * @tx_tr:      transmit tail room
 * @rx_tr:      receive tail room
 * @mtu:        transmit max size
 * @mru:        receive max size
 * @allocsz:    size of dma memory reserved for TX buffers
 * @alloc_addr: virtual address to dma memory for TX buffers
 * @alloc_dma:  dma address to dma memory for TX buffers
 * @genpool:    Gen Pool used for allocating TX buffers
 * @reserved_mem: Pointer to memory reserve allocated from genpool
 * @reserved_size: Size of memory reserve allocated from genpool
 * @stats:       Statistics exposed in sysfs
 * @debugfs:    Debugfs dentry for statistic counters
 */
struct cfv_info {
        struct caif_dev_common cfdev;
        struct virtio_device *vdev;
        struct vringh *vr_rx;
        struct virtqueue *vq_tx;
        struct net_device *ndev;
        unsigned int watermark_tx;
        /* Protect access to vq_tx */
        spinlock_t tx_lock;
        struct tasklet_struct tx_release_tasklet;
        struct napi_struct napi;
        struct cfv_napi_context ctx;
        u16 tx_hr;
        u16 rx_hr;
        u16 tx_tr;
        u16 rx_tr;
        u32 mtu;
        u32 mru;
        size_t allocsz;
        void *alloc_addr;
        dma_addr_t alloc_dma;
        struct gen_pool *genpool;
        unsigned long reserved_mem;
        size_t reserved_size;
        struct cfv_stats stats;
        struct dentry *debugfs;
};

/* struct buf_info - maintains transmit buffer data handle
 * @size:       size of transmit buffer
 * @dma_handle: handle to allocated dma device memory area
 * @vaddr:      virtual address mapping to allocated memory area
 */
struct buf_info {
        size_t size;
        u8 *vaddr;
};

/* Called from virtio device, in IRQ context */
static void cfv_release_cb(struct virtqueue *vq_tx)
{
        struct cfv_info *cfv = vq_tx->vdev->priv;

        ++cfv->stats.tx_kicks;
        tasklet_schedule(&cfv->tx_release_tasklet);
}

static void free_buf_info(struct cfv_info *cfv, struct buf_info *buf_info)
{
        if (!buf_info)
                return;
        gen_pool_free(cfv->genpool, (unsigned long) buf_info->vaddr,
                      buf_info->size);
        kfree(buf_info);
}

/* This is invoked whenever the remote processor completed processing
 * a TX msg we just sent, and the buffer is put back to the used ring.
 */
static void cfv_release_used_buf(struct virtqueue *vq_tx)
{
        struct cfv_info *cfv = vq_tx->vdev->priv;
        unsigned long flags;

        BUG_ON(vq_tx != cfv->vq_tx);

        for (;;) {
                unsigned int len;
                struct buf_info *buf_info;

                /* Get used buffer from used ring to recycle used descriptors */
                spin_lock_irqsave(&cfv->tx_lock, flags);
                buf_info = virtqueue_get_buf(vq_tx, &len);
                spin_unlock_irqrestore(&cfv->tx_lock, flags);

                /* Stop looping if there are no more buffers to free */
                if (!buf_info)
                        break;

                free_buf_info(cfv, buf_info);

                /* watermark_tx indicates if we previously stopped the tx
                 * queues. If we have enough free stots in the virtio ring,
                 * re-establish memory reserved and open up tx queues.
                 */
                if (cfv->vq_tx->num_free <= cfv->watermark_tx)
                        continue;

                /* Re-establish memory reserve */
                if (cfv->reserved_mem == 0 && cfv->genpool)
                        cfv->reserved_mem =
                                gen_pool_alloc(cfv->genpool,
                                               cfv->reserved_size);

                /* Open up the tx queues */
                if (cfv->reserved_mem) {
                        cfv->watermark_tx =
                                virtqueue_get_vring_size(cfv->vq_tx);
                        netif_tx_wake_all_queues(cfv->ndev);
                        /* Buffers are recycled in cfv_netdev_tx, so
                         * disable notifications when queues are opened.
                         */
                        virtqueue_disable_cb(cfv->vq_tx);
                        ++cfv->stats.tx_flow_on;
                } else {
                        /* if no memory reserve, wait for more free slots */
                        WARN_ON(cfv->watermark_tx >
                               virtqueue_get_vring_size(cfv->vq_tx));
                        cfv->watermark_tx +=
                                virtqueue_get_vring_size(cfv->vq_tx) / 4;
                }
        }
}

/* Allocate a SKB and copy packet data to it */
static struct sk_buff *cfv_alloc_and_copy_skb(int *err,
                                              struct cfv_info *cfv,
                                              u8 *frm, u32 frm_len)
{
        struct sk_buff *skb;
        u32 cfpkt_len, pad_len;

        *err = 0;
        /* Verify that packet size with down-link header and mtu size */
        if (frm_len > cfv->mru || frm_len <= cfv->rx_hr + cfv->rx_tr) {
                netdev_err(cfv->ndev,
                           "Invalid frmlen:%u  mtu:%u hr:%d tr:%d\n",
                           frm_len, cfv->mru,  cfv->rx_hr,
                           cfv->rx_tr);
                *err = -EPROTO;
                return NULL;
        }

        cfpkt_len = frm_len - (cfv->rx_hr + cfv->rx_tr);
        pad_len = (unsigned long)(frm + cfv->rx_hr) & (IP_HDR_ALIGN - 1);

        skb = netdev_alloc_skb(cfv->ndev, frm_len + pad_len);
        if (!skb) {
                *err = -ENOMEM;
                return NULL;
        }

        skb_reserve(skb, cfv->rx_hr + pad_len);

        memcpy(skb_put(skb, cfpkt_len), frm + cfv->rx_hr, cfpkt_len);
        return skb;
}

/* Get packets from the host vring */
static int cfv_rx_poll(struct napi_struct *napi, int quota)
{
        struct cfv_info *cfv = container_of(napi, struct cfv_info, napi);
        int rxcnt = 0;
        int err = 0;
        void *buf;
        struct sk_buff *skb;
        struct vringh_kiov *riov = &cfv->ctx.riov;
        unsigned int skb_len;

again:
        do {
                skb = NULL;

                /* Put the previous iovec back on the used ring and
                 * fetch a new iovec if we have processed all elements.
                 */
                if (riov->i == riov->used) {
                        if (cfv->ctx.head != USHRT_MAX) {
                                vringh_complete_kern(cfv->vr_rx,
                                                     cfv->ctx.head,
                                                     0);
                                cfv->ctx.head = USHRT_MAX;
                        }

                        err = vringh_getdesc_kern(
                                cfv->vr_rx,
                                riov,
                                NULL,
                                &cfv->ctx.head,
                                GFP_ATOMIC);

                        if (err <= 0)
                                goto exit;
                }

                buf = phys_to_virt((unsigned long) riov->iov[riov->i].iov_base);
                /* TODO: Add check on valid buffer address */

                skb = cfv_alloc_and_copy_skb(&err, cfv, buf,
                                             riov->iov[riov->i].iov_len);
                if (unlikely(err))
                        goto exit;

                /* Push received packet up the stack. */
                skb_len = skb->len;
                skb->protocol = htons(ETH_P_CAIF);
                skb_reset_mac_header(skb);
                skb->dev = cfv->ndev;
                err = netif_receive_skb(skb);
                if (unlikely(err)) {
                        ++cfv->ndev->stats.rx_dropped;
                } else {
                        ++cfv->ndev->stats.rx_packets;
                        cfv->ndev->stats.rx_bytes += skb_len;
                }

                ++riov->i;
                ++rxcnt;
        } while (rxcnt < quota);

        ++cfv->stats.rx_napi_resched;
        goto out;

exit:
        switch (err) {
        case 0:
                ++cfv->stats.rx_napi_complete;

                /* Really out of patckets? (stolen from virtio_net)*/
                napi_complete(napi);
                if (unlikely(!vringh_notify_enable_kern(cfv->vr_rx)) &&
                    napi_schedule_prep(napi)) {
                        vringh_notify_disable_kern(cfv->vr_rx);
                        __napi_schedule(napi);
                        goto again;
                }
                break;

        case -ENOMEM:
                ++cfv->stats.rx_nomem;
                dev_kfree_skb(skb);
                /* Stop NAPI poll on OOM, we hope to be polled later */
                napi_complete(napi);
                vringh_notify_enable_kern(cfv->vr_rx);
                break;

        default:
                /* We're doomed, any modem fault is fatal */
                netdev_warn(cfv->ndev, "Bad ring, disable device\n");
                cfv->ndev->stats.rx_dropped = riov->used - riov->i;
                napi_complete(napi);
                vringh_notify_disable_kern(cfv->vr_rx);
                netif_carrier_off(cfv->ndev);
                break;
        }
out:
        if (rxcnt && vringh_need_notify_kern(cfv->vr_rx) > 0)
                vringh_notify(cfv->vr_rx);
        return rxcnt;
}

static void cfv_recv(struct virtio_device *vdev, struct vringh *vr_rx)
{
        struct cfv_info *cfv = vdev->priv;

        ++cfv->stats.rx_kicks;
        vringh_notify_disable_kern(cfv->vr_rx);
        napi_schedule(&cfv->napi);
}

static void cfv_destroy_genpool(struct cfv_info *cfv)
{
        if (cfv->alloc_addr)
                dma_free_coherent(cfv->vdev->dev.parent->parent,
                                  cfv->allocsz, cfv->alloc_addr,
                                  cfv->alloc_dma);

        if (!cfv->genpool)
                return;
        gen_pool_free(cfv->genpool,  cfv->reserved_mem,
                      cfv->reserved_size);
        gen_pool_destroy(cfv->genpool);
        cfv->genpool = NULL;
}

static int cfv_create_genpool(struct cfv_info *cfv)
{
        int err;

        /* dma_alloc can only allocate whole pages, and we need a more
         * fine graned allocation so we use genpool. We ask for space needed
         * by IP and a full ring. If the dma allcoation fails we retry with a
         * smaller allocation size.
         */
        err = -ENOMEM;
        cfv->allocsz = (virtqueue_get_vring_size(cfv->vq_tx) *
                        (ETH_DATA_LEN + cfv->tx_hr + cfv->tx_tr) * 11)/10;
        if (cfv->allocsz <= (num_possible_cpus() + 1) * cfv->ndev->mtu)
                return -EINVAL;

        for (;;) {
                if (cfv->allocsz <= num_possible_cpus() * cfv->ndev->mtu) {
                        netdev_info(cfv->ndev, "Not enough device memory\n");
                        return -ENOMEM;
                }

                cfv->alloc_addr = dma_alloc_coherent(
                                                cfv->vdev->dev.parent->parent,
                                                cfv->allocsz, &cfv->alloc_dma,
                                                GFP_ATOMIC);
                if (cfv->alloc_addr)
                        break;

                cfv->allocsz = (cfv->allocsz * 3) >> 2;
        }

        netdev_dbg(cfv->ndev, "Allocated %zd bytes from dma-memory\n",
                   cfv->allocsz);

        /* Allocate on 128 bytes boundaries (1 << 7)*/
        cfv->genpool = gen_pool_create(7, -1);
        if (!cfv->genpool)
                goto err;

        err = gen_pool_add_virt(cfv->genpool, (unsigned long)cfv->alloc_addr,
                                (phys_addr_t)virt_to_phys(cfv->alloc_addr),
                                cfv->allocsz, -1);
        if (err)
                goto err;

        /* Reserve some memory for low memory situations. If we hit the roof
         * in the memory pool, we stop TX flow and release the reserve.
         */
        cfv->reserved_size = num_possible_cpus() * cfv->ndev->mtu;
        cfv->reserved_mem = gen_pool_alloc(cfv->genpool,
                                           cfv->reserved_size);
        if (!cfv->reserved_mem) {
                err = -ENOMEM;
                goto err;
        }

        cfv->watermark_tx = virtqueue_get_vring_size(cfv->vq_tx);
        return 0;
err:
        cfv_destroy_genpool(cfv);
        return err;
}

/* Enable the CAIF interface and allocate the memory-pool */
static int cfv_netdev_open(struct net_device *netdev)
{
        struct cfv_info *cfv = netdev_priv(netdev);

        if (cfv_create_genpool(cfv))
                return -ENOMEM;

        netif_carrier_on(netdev);
        napi_enable(&cfv->napi);

        /* Schedule NAPI to read any pending packets */
        napi_schedule(&cfv->napi);
        return 0;
}

/* Disable the CAIF interface and free the memory-pool */
static int cfv_netdev_close(struct net_device *netdev)
{
        struct cfv_info *cfv = netdev_priv(netdev);
        unsigned long flags;
        struct buf_info *buf_info;

        /* Disable interrupts, queues and NAPI polling */
        netif_carrier_off(netdev);
        virtqueue_disable_cb(cfv->vq_tx);
        vringh_notify_disable_kern(cfv->vr_rx);
        napi_disable(&cfv->napi);

        /* Release any TX buffers on both used and avilable rings */
        cfv_release_used_buf(cfv->vq_tx);
        spin_lock_irqsave(&cfv->tx_lock, flags);
        while ((buf_info = virtqueue_detach_unused_buf(cfv->vq_tx)))
                free_buf_info(cfv, buf_info);
        spin_unlock_irqrestore(&cfv->tx_lock, flags);

        /* Release all dma allocated memory and destroy the pool */
        cfv_destroy_genpool(cfv);
        return 0;
}

/* Allocate a buffer in dma-memory and copy skb to it */
static struct buf_info *cfv_alloc_and_copy_to_shm(struct cfv_info *cfv,
                                                       struct sk_buff *skb,
                                                       struct scatterlist *sg)
{
        struct caif_payload_info *info = (void *)&skb->cb;
        struct buf_info *buf_info = NULL;
        u8 pad_len, hdr_ofs;

        if (!cfv->genpool)
                goto err;

        if (unlikely(cfv->tx_hr + skb->len + cfv->tx_tr > cfv->mtu)) {
                netdev_warn(cfv->ndev, "Invalid packet len (%d > %d)\n",
                            cfv->tx_hr + skb->len + cfv->tx_tr, cfv->mtu);
                goto err;
        }

        buf_info = kmalloc(sizeof(struct buf_info), GFP_ATOMIC);
        if (unlikely(!buf_info))
                goto err;

        /* Make the IP header aligned in tbe buffer */
        hdr_ofs = cfv->tx_hr + info->hdr_len;
        pad_len = hdr_ofs & (IP_HDR_ALIGN - 1);
        buf_info->size = cfv->tx_hr + skb->len + cfv->tx_tr + pad_len;

        /* allocate dma memory buffer */
        buf_info->vaddr = (void *)gen_pool_alloc(cfv->genpool, buf_info->size);
        if (unlikely(!buf_info->vaddr))
                goto err;

        /* copy skbuf contents to send buffer */
        skb_copy_bits(skb, 0, buf_info->vaddr + cfv->tx_hr + pad_len, skb->len);
        sg_init_one(sg, buf_info->vaddr + pad_len,
                    skb->len + cfv->tx_hr + cfv->rx_hr);

        return buf_info;
err:
        kfree(buf_info);
        return NULL;
}

/* Put the CAIF packet on the virtio ring and kick the receiver */
static int cfv_netdev_tx(struct sk_buff *skb, struct net_device *netdev)
{
        struct cfv_info *cfv = netdev_priv(netdev);
        struct buf_info *buf_info;
        struct scatterlist sg;
        unsigned long flags;
        bool flow_off = false;
        int ret;

        /* garbage collect released buffers */
        cfv_release_used_buf(cfv->vq_tx);
        spin_lock_irqsave(&cfv->tx_lock, flags);

        /* Flow-off check takes into account number of cpus to make sure
         * virtqueue will not be overfilled in any possible smp conditions.
         *
         * Flow-on is triggered when sufficient buffers are freed
         */
        if (unlikely(cfv->vq_tx->num_free <= num_present_cpus())) {
                flow_off = true;
                cfv->stats.tx_full_ring++;
        }

        /* If we run out of memory, we release the memory reserve and retry
         * allocation.
         */
        buf_info = cfv_alloc_and_copy_to_shm(cfv, skb, &sg);
        if (unlikely(!buf_info)) {
                cfv->stats.tx_no_mem++;
                flow_off = true;

                if (cfv->reserved_mem && cfv->genpool) {
                        gen_pool_free(cfv->genpool,  cfv->reserved_mem,
                                      cfv->reserved_size);
                        cfv->reserved_mem = 0;
                        buf_info = cfv_alloc_and_copy_to_shm(cfv, skb, &sg);
                }
        }

        if (unlikely(flow_off)) {
                /* Turn flow on when a 1/4 of the descriptors are released */
                cfv->watermark_tx = virtqueue_get_vring_size(cfv->vq_tx) / 4;
                /* Enable notifications of recycled TX buffers */
                virtqueue_enable_cb(cfv->vq_tx);
                netif_tx_stop_all_queues(netdev);
        }

        if (unlikely(!buf_info)) {
                /* If the memory reserve does it's job, this shouldn't happen */
                netdev_warn(cfv->ndev, "Out of gen_pool memory\n");
                goto err;
        }

        ret = virtqueue_add_outbuf(cfv->vq_tx, &sg, 1, buf_info, GFP_ATOMIC);
        if (unlikely((ret < 0))) {
                /* If flow control works, this shouldn't happen */
                netdev_warn(cfv->ndev, "Failed adding buffer to TX vring:%d\n",
                            ret);
                goto err;
        }

        /* update netdev statistics */
        cfv->ndev->stats.tx_packets++;
        cfv->ndev->stats.tx_bytes += skb->len;
        spin_unlock_irqrestore(&cfv->tx_lock, flags);

        /* tell the remote processor it has a pending message to read */
        virtqueue_kick(cfv->vq_tx);

        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
err:
        spin_unlock_irqrestore(&cfv->tx_lock, flags);
        cfv->ndev->stats.tx_dropped++;
        free_buf_info(cfv, buf_info);
        dev_kfree_skb(skb);
        return NETDEV_TX_OK;
}

static void cfv_tx_release_tasklet(unsigned long drv)
{
        struct cfv_info *cfv = (struct cfv_info *)drv;
        cfv_release_used_buf(cfv->vq_tx);
}

static const struct net_device_ops cfv_netdev_ops = {
        .ndo_open = cfv_netdev_open,
        .ndo_stop = cfv_netdev_close,
        .ndo_start_xmit = cfv_netdev_tx,
};

static void cfv_netdev_setup(struct net_device *netdev)
{
        netdev->netdev_ops = &cfv_netdev_ops;
        netdev->type = ARPHRD_CAIF;
        netdev->tx_queue_len = 100;
        netdev->flags = IFF_POINTOPOINT | IFF_NOARP;
        netdev->mtu = CFV_DEF_MTU_SIZE;
        netdev->destructor = free_netdev;
}

/* Create debugfs counters for the device */
static inline void debugfs_init(struct cfv_info *cfv)
{
        cfv->debugfs =
                debugfs_create_dir(netdev_name(cfv->ndev), NULL);

        if (IS_ERR(cfv->debugfs))
                return;

        debugfs_create_u32("rx-napi-complete", S_IRUSR, cfv->debugfs,
                           &cfv->stats.rx_napi_complete);
        debugfs_create_u32("rx-napi-resched", S_IRUSR, cfv->debugfs,
                           &cfv->stats.rx_napi_resched);
        debugfs_create_u32("rx-nomem", S_IRUSR, cfv->debugfs,
                           &cfv->stats.rx_nomem);
        debugfs_create_u32("rx-kicks", S_IRUSR, cfv->debugfs,
                           &cfv->stats.rx_kicks);
        debugfs_create_u32("tx-full-ring", S_IRUSR, cfv->debugfs,
                           &cfv->stats.tx_full_ring);
        debugfs_create_u32("tx-no-mem", S_IRUSR, cfv->debugfs,
                           &cfv->stats.tx_no_mem);
        debugfs_create_u32("tx-kicks", S_IRUSR, cfv->debugfs,
                           &cfv->stats.tx_kicks);
        debugfs_create_u32("tx-flow-on", S_IRUSR, cfv->debugfs,
                           &cfv->stats.tx_flow_on);
}

/* Setup CAIF for the a virtio device */
static int cfv_probe(struct virtio_device *vdev)
{
        vq_callback_t *vq_cbs = cfv_release_cb;
        vrh_callback_t *vrh_cbs = cfv_recv;
        const char *names =  "output";
        const char *cfv_netdev_name = "cfvrt";
        struct net_device *netdev;
        struct cfv_info *cfv;
        int err = -EINVAL;

        netdev = alloc_netdev(sizeof(struct cfv_info), cfv_netdev_name,
                              cfv_netdev_setup);
        if (!netdev)
                return -ENOMEM;

        cfv = netdev_priv(netdev);
        cfv->vdev = vdev;
        cfv->ndev = netdev;

        spin_lock_init(&cfv->tx_lock);

        /* Get the RX virtio ring. This is a "host side vring". */
        err = -ENODEV;
        if (!vdev->vringh_config || !vdev->vringh_config->find_vrhs)
                goto err;

        err = vdev->vringh_config->find_vrhs(vdev, 1, &cfv->vr_rx, &vrh_cbs);
        if (err)
                goto err;

        /* Get the TX virtio ring. This is a "guest side vring". */
        err = vdev->config->find_vqs(vdev, 1, &cfv->vq_tx, &vq_cbs, &names);
        if (err)
                goto err;

        /* Get the CAIF configuration from virtio config space, if available */
#define GET_VIRTIO_CONFIG_OPS(_v, _var, _f) \
        ((_v)->config->get(_v, offsetof(struct virtio_caif_transf_config, _f), \
                           &_var, \
                           FIELD_SIZEOF(struct virtio_caif_transf_config, _f)))

        if (vdev->config->get) {
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->tx_hr, headroom);
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->rx_hr, headroom);
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->tx_tr, tailroom);
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->rx_tr, tailroom);
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->mtu, mtu);
                GET_VIRTIO_CONFIG_OPS(vdev, cfv->mru, mtu);
        } else {
                cfv->tx_hr = CFV_DEF_HEADROOM;
                cfv->rx_hr = CFV_DEF_HEADROOM;
                cfv->tx_tr = CFV_DEF_TAILROOM;
                cfv->rx_tr = CFV_DEF_TAILROOM;
                cfv->mtu = CFV_DEF_MTU_SIZE;
                cfv->mru = CFV_DEF_MTU_SIZE;
        }

        netdev->needed_headroom = cfv->tx_hr;
        netdev->needed_tailroom = cfv->tx_tr;

        /* Disable buffer release interrupts unless we have stopped TX queues */
        virtqueue_disable_cb(cfv->vq_tx);

        netdev->mtu = cfv->mtu - cfv->tx_tr;
        vdev->priv = cfv;

        /* Initialize NAPI poll context data */
        vringh_kiov_init(&cfv->ctx.riov, NULL, 0);
        cfv->ctx.head = USHRT_MAX;
        netif_napi_add(netdev, &cfv->napi, cfv_rx_poll, CFV_DEFAULT_QUOTA);

        tasklet_init(&cfv->tx_release_tasklet,
                     cfv_tx_release_tasklet,
                     (unsigned long)cfv);

        /* Carrier is off until netdevice is opened */
        netif_carrier_off(netdev);

        /* register Netdev */
        err = register_netdev(netdev);
        if (err) {
                dev_err(&vdev->dev, "Unable to register netdev (%d)\n", err);
                goto err;
        }

        debugfs_init(cfv);

        return 0;
err:
        netdev_warn(cfv->ndev, "CAIF Virtio probe failed:%d\n", err);

        if (cfv->vr_rx)
                vdev->vringh_config->del_vrhs(cfv->vdev);
        if (cfv->vdev)
                vdev->config->del_vqs(cfv->vdev);
        free_netdev(netdev);
        return err;
}

static void cfv_remove(struct virtio_device *vdev)
{
        struct cfv_info *cfv = vdev->priv;

        rtnl_lock();
        dev_close(cfv->ndev);
        rtnl_unlock();

        tasklet_kill(&cfv->tx_release_tasklet);
        debugfs_remove_recursive(cfv->debugfs);

        vringh_kiov_cleanup(&cfv->ctx.riov);
        vdev->config->reset(vdev);
        vdev->vringh_config->del_vrhs(cfv->vdev);
        cfv->vr_rx = NULL;
        vdev->config->del_vqs(cfv->vdev);
        unregister_netdev(cfv->ndev);
}

static struct virtio_device_id id_table[] = {
        { VIRTIO_ID_CAIF, VIRTIO_DEV_ANY_ID },
        { 0 },
};

static unsigned int features[] = {
};

static struct virtio_driver caif_virtio_driver = {
        .feature_table          = features,
        .feature_table_size     = ARRAY_SIZE(features),
        .driver.name            = KBUILD_MODNAME,
        .driver.owner           = THIS_MODULE,
        .id_table               = id_table,
        .probe                  = cfv_probe,
        .remove                 = cfv_remove,
};

module_virtio_driver(caif_virtio_driver);
MODULE_DEVICE_TABLE(virtio, id_table);