caif_virtio: Introduce caif over virtio

Add the CAIF Virtio shared memory driver for talking
to a modem.

This CAIF Link layer communicates to the modem over
shared memory. It is implemented as a virtio_driver.
The underlying virtio device is managed by the remoteproc
framework. The Virtio queue is used for transmitting data
to the modem, and the new vringh is used for receiving data.

Genalloc is used for managing the shared memory used for TX
data. The default dma-alloc-coherent allocator can only
allocate whole pages, and this wastes too much shared memory.

Flow control is implemented by stopping the TX-queues if the
virtio queues go full or we run out of memory. Queued are
reopened when queues are below the watermark.

NAPI is used in RX path, and a dedicated tasklet is used
for releasing TX buffers.

Signed-off-by: Erwan Yvin <erwan.yvin@stericsson.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (minor fixes)

5 files changed, 827 insertions, 0 deletions

diff --git a/drivers/net/caif/Kconfig b/drivers/net/caif/Kconfig
index 60c2142373c9..893f9154011e 100644
--- a/drivers/net/caif/Kconfig
+++ b/drivers/net/caif/Kconfig
@@ -47,3 +47,17 @@ config CAIF_HSI
        The caif low level driver for CAIF over HSI.
        Be aware that if you enable this then you also need to
        enable a low-level HSI driver.
+
+config CAIF_VIRTIO
+	tristate "CAIF virtio transport driver"
+	depends on CAIF
+	select VHOST_RING
+	select VIRTIO
+	select GENERIC_ALLOCATOR
+	default n
+	---help---
+	The caif driver for CAIF over Virtio.
+
+if CAIF_VIRTIO
+source "drivers/vhost/Kconfig"
+endif
diff --git a/drivers/net/caif/Makefile b/drivers/net/caif/Makefile
index 91dff861560f..d9ee26a96c6e 100644
--- a/drivers/net/caif/Makefile
+++ b/drivers/net/caif/Makefile
@@ -13,3 +13,6 @@ obj-$(CONFIG_CAIF_SHM) += caif_shm.o
 
 # HSI interface
 obj-$(CONFIG_CAIF_HSI) += caif_hsi.o
+
+# Virtio interface
+obj-$(CONFIG_CAIF_VIRTIO) += caif_virtio.o
diff --git a/drivers/net/caif/caif_virtio.c b/drivers/net/caif/caif_virtio.c
new file mode 100644
index 000000000000..b1e1205e4e28
--- /dev/null
+++ b/drivers/net/caif/caif_virtio.c
@@ -0,0 +1,785 @@
+/*
+ * Copyright (C) ST-Ericsson AB 2013
+ * Authors: Vicram Arv / vikram.arv@stericsson.com,
+ *	    Dmitry Tarnyagin / dmitry.tarnyagin@stericsson.com
+ *	    Sjur Brendeland / sjur.brandeland@stericsson.com
+ * 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 <vikram.arv@stericsson.com>");
+MODULE_AUTHOR("Sjur Brendeland <sjur.brandeland@stericsson.com>");
+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)
+		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_buf(cfv->vq_tx, &sg, 1, 0,
+				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 = 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);
diff --git a/include/linux/virtio_caif.h b/include/linux/virtio_caif.h
new file mode 100644
index 000000000000..5d2d3124ca3d
--- /dev/null
+++ b/include/linux/virtio_caif.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright (C) ST-Ericsson AB 2012
+ * Author: Sjur Brændeland <sjur.brandeland@stericsson.com>
+ *
+ * This header is BSD licensed so
+ * anyone can use the definitions to implement compatible remote processors
+ */
+
+#ifndef VIRTIO_CAIF_H
+#define VIRTIO_CAIF_H
+
+#include <linux/types.h>
+struct virtio_caif_transf_config {
+	u16 headroom;
+	u16 tailroom;
+	u32 mtu;
+	u8 reserved[4];
+};
+
+struct virtio_caif_config {
+	struct virtio_caif_transf_config uplink, downlink;
+	u8 reserved[8];
+};
+#endif
diff --git a/include/uapi/linux/virtio_ids.h b/include/uapi/linux/virtio_ids.h
index a7630d04029f..284fc3a05f7b 100644
--- a/include/uapi/linux/virtio_ids.h
+++ b/include/uapi/linux/virtio_ids.h
@@ -38,5 +38,6 @@
 #define VIRTIO_ID_SCSI		8 /* virtio scsi */
 #define VIRTIO_ID_9P		9 /* 9p virtio console */
 #define VIRTIO_ID_RPROC_SERIAL 11 /* virtio remoteproc serial link */
+#define VIRTIO_ID_CAIF	       12 /* Virtio caif */
 
 #endif /* _LINUX_VIRTIO_IDS_H */