Re: [PATCH v11] can: virtio: Add virtio CAN driver

[Matias Ezequiel Vara Larsen <mvaralar@redhat.com>]

FYI, the nipa/ai-review bot found these problems:

https://netdev-ai.bots.linux.dev/ai-review.html?id=1acd3843-3565-4b65-94e9-d793bdf3b5e7

I will address them and resubmit the patch.

> diff --git a/MAINTAINERS b/MAINTAINERS
> index 80cd3498c293..f295a904c93e 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -27068,6 +27068,15 @@ F:	drivers/scsi/virtio_scsi.c
>  F:	include/uapi/linux/virtio_blk.h
>  F:	include/uapi/linux/virtio_scsi.h
>  
> +VIRTIO CAN DRIVER
> +M:	"Harald Mommer" <harald.mommer@oss.qualcomm.com>
> +M:	"Matias Ezequiel Vara Larsen" <mvaralar@redhat.com>
> +L:	virtualization@lists.linux.dev
> +L:	linux-can@vger.kernel.org
> +S:	Maintained
> +F:	drivers/net/can/virtio_can.c
> +F:	include/uapi/linux/virtio_can.h
> +
>  VIRTIO CONSOLE DRIVER
>  M:	Amit Shah <amit@kernel.org>
>  L:	virtualization@lists.linux.dev
> diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
> index d43d56694667..f33ae46d9766 100644
> --- a/drivers/net/can/Kconfig
> +++ b/drivers/net/can/Kconfig
> @@ -209,6 +209,18 @@ config CAN_TI_HECC
>  	  Driver for TI HECC (High End CAN Controller) module found on many
>  	  TI devices. The device specifications are available from www.ti.com
>  
> +config CAN_VIRTIO_CAN
> +	depends on VIRTIO
> +	tristate "Virtio CAN device support"
> +	default n
> +	help
> +	  Say Y here if you want to support for Virtio CAN.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called virtio-can.
> +
> +	  If unsure, say N.
> +
>  config CAN_XILINXCAN
>  	tristate "Xilinx CAN"
>  	depends on ARCH_ZYNQ || ARM64 || MICROBLAZE || COMPILE_TEST
> diff --git a/drivers/net/can/Makefile b/drivers/net/can/Makefile
> index 56138d8ddfd2..2ddea733ed5d 100644
> --- a/drivers/net/can/Makefile
> +++ b/drivers/net/can/Makefile
> @@ -32,6 +32,7 @@ obj-$(CONFIG_CAN_PEAK_PCIEFD)	+= peak_canfd/
>  obj-$(CONFIG_CAN_SJA1000)	+= sja1000/
>  obj-$(CONFIG_CAN_SUN4I)		+= sun4i_can.o
>  obj-$(CONFIG_CAN_TI_HECC)	+= ti_hecc.o
> +obj-$(CONFIG_CAN_VIRTIO_CAN)	+= virtio_can.o
>  obj-$(CONFIG_CAN_XILINXCAN)	+= xilinx_can.o
>  
>  subdir-ccflags-$(CONFIG_CAN_DEBUG_DEVICES) += -DDEBUG
> diff --git a/drivers/net/can/virtio_can.c b/drivers/net/can/virtio_can.c
> new file mode 100644
> index 000000000000..56031f840caa
> --- /dev/null
> +++ b/drivers/net/can/virtio_can.c
> @@ -0,0 +1,964 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * CAN bus driver for the Virtio CAN controller
> + *
> + * Copyright (C) 2021-2023 OpenSynergy GmbH
> + * Copyright Red Hat, Inc. 2025
> + */
> +
> +#include <linux/atomic.h>
> +#include <linux/idr.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/netdevice.h>
> +#include <linux/stddef.h>
> +#include <linux/can/dev.h>
> +#include <linux/virtio.h>
> +#include <linux/virtio_ring.h>
> +#include <linux/virtio_can.h>
> +
> +/* CAN device queues */
> +#define VIRTIO_CAN_QUEUE_TX 0
> +#define VIRTIO_CAN_QUEUE_RX 1
> +#define VIRTIO_CAN_QUEUE_CONTROL 2
> +#define VIRTIO_CAN_QUEUE_COUNT 3
> +
> +#define CAN_KNOWN_FLAGS \
> +	(VIRTIO_CAN_FLAGS_EXTENDED |\
> +	 VIRTIO_CAN_FLAGS_FD |\
> +	 VIRTIO_CAN_FLAGS_RTR)
> +
> +/* Max. number of in flight TX messages */
> +#define VIRTIO_CAN_ECHO_SKB_MAX 128
> +
> +struct virtio_can_tx {
> +	unsigned int putidx;
> +	struct virtio_can_tx_in tx_in;
> +	/* Keep virtio_can_tx_out at the end of the structure due to flex array */
> +	struct virtio_can_tx_out tx_out;
> +};
> +
> +struct virtio_can_control {
> +	struct virtio_can_control_out cpkt_out;
> +	struct virtio_can_control_in cpkt_in;
> +};
> +
> +/* virtio_can private data structure */
> +struct virtio_can_priv {
> +	struct can_priv can;	/* must be the first member */
> +	/* NAPI for RX messages */
> +	struct napi_struct napi;
> +	/* NAPI for TX messages */
> +	struct napi_struct napi_tx;
> +	/* The network device we're associated with */
> +	struct net_device *dev;
> +	/* The virtio device we're associated with */
> +	struct virtio_device *vdev;
> +	/* The virtqueues */
> +	struct virtqueue *vqs[VIRTIO_CAN_QUEUE_COUNT];
> +	/* Lock for TX operations */
> +	spinlock_t tx_lock;
> +	/* Control queue lock */
> +	struct mutex ctrl_lock;
> +	/* Wait for control queue processing without polling */
> +	struct completion ctrl_done;
> +	/* Array of receive queue messages */
> +	struct virtio_can_rx *rpkt;
> +	struct virtio_can_control can_ctr_msg;
> +	/* Data to get and maintain the putidx for local TX echo */
> +	struct ida tx_putidx_ida;
> +	/* In flight TX messages */
> +	atomic_t tx_inflight;
> +	/* Packet length */
> +	int rpkt_len;
> +	/* BusOff pending. Reset after successful indication to upper layer */
> +	bool busoff_pending;
> +};
> +
> +static void virtqueue_napi_schedule(struct napi_struct *napi,
> +				    struct virtqueue *vq)
> +{
> +	if (napi_schedule_prep(napi)) {
> +		virtqueue_disable_cb(vq);
> +		__napi_schedule(napi);
> +	}
> +}
> +
> +static void virtqueue_napi_complete(struct napi_struct *napi,
> +				    struct virtqueue *vq, int processed)
> +{
> +	int opaque;
> +
> +	opaque = virtqueue_enable_cb_prepare(vq);
> +	if (napi_complete_done(napi, processed)) {
> +		if (unlikely(virtqueue_poll(vq, opaque)))
> +			virtqueue_napi_schedule(napi, vq);
> +	} else {
> +		virtqueue_disable_cb(vq);
> +	}
> +}
> +
> +static void virtio_can_free_candev(struct net_device *ndev)
> +{
> +	struct virtio_can_priv *priv = netdev_priv(ndev);
> +
> +	ida_destroy(&priv->tx_putidx_ida);
> +	free_candev(ndev);
> +}
> +
> +static int virtio_can_alloc_tx_idx(struct virtio_can_priv *priv)
> +{
> +	int tx_idx;
> +
> +	tx_idx = ida_alloc_max(&priv->tx_putidx_ida,
> +			       priv->can.echo_skb_max - 1, GFP_ATOMIC);
> +	if (tx_idx >= 0)
> +		atomic_inc(&priv->tx_inflight);
> +
> +	return tx_idx;
> +}
> +
> +static void virtio_can_free_tx_idx(struct virtio_can_priv *priv,
> +				   unsigned int idx)
> +{
> +	ida_free(&priv->tx_putidx_ida, idx);
> +	atomic_dec(&priv->tx_inflight);
> +}
> +
> +/* Create a scatter-gather list representing our input buffer and put
> + * it in the queue.
> + *
> + * Callers should take appropriate locks.
> + */
> +static int virtio_can_add_inbuf(struct virtqueue *vq, void *buf,
> +				unsigned int size)
> +{
> +	struct scatterlist sg[1];
> +	int ret;
> +
> +	sg_init_one(sg, buf, size);
> +
> +	ret = virtqueue_add_inbuf(vq, sg, 1, buf, GFP_ATOMIC);
> +
> +	return ret;
> +}
> +
> +/* Send a control message with message type either
> + *
> + * - VIRTIO_CAN_SET_CTRL_MODE_START or
> + * - VIRTIO_CAN_SET_CTRL_MODE_STOP.
> + *
> + */
> +static u8 virtio_can_send_ctrl_msg(struct net_device *ndev, u16 msg_type)
> +{
> +	struct scatterlist sg_out, sg_in, *sgs[2] = { &sg_out, &sg_in };
> +	struct virtio_can_priv *priv = netdev_priv(ndev);
> +	struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_CONTROL];
> +	struct device *dev = &priv->vdev->dev;
> +	unsigned int len;
> +	int err;
> +
> +	guard(mutex)(&priv->ctrl_lock);
> +
> +	priv->can_ctr_msg.cpkt_out.msg_type = cpu_to_le16(msg_type);
> +	sg_init_one(&sg_out, &priv->can_ctr_msg.cpkt_out,
> +		    sizeof(priv->can_ctr_msg.cpkt_out));
> +	sg_init_one(&sg_in, &priv->can_ctr_msg.cpkt_in, sizeof(priv->can_ctr_msg.cpkt_in));
> +
> +	err = virtqueue_add_sgs(vq, sgs, 1u, 1u, priv, GFP_ATOMIC);
> +	if (err != 0) {
> +		dev_err(dev, "%s(): virtqueue_add_sgs() failed\n", __func__);
> +		return VIRTIO_CAN_RESULT_NOT_OK;
> +	}
> +
> +	if (!virtqueue_kick(vq)) {
> +		dev_err(dev, "%s(): Kick failed\n", __func__);
> +		return VIRTIO_CAN_RESULT_NOT_OK;
> +	}
> +
> +	while (!virtqueue_get_buf(vq, &len) && !virtqueue_is_broken(vq))
> +		wait_for_completion(&priv->ctrl_done);
> +
> +	return priv->can_ctr_msg.cpkt_in.result;
> +}
> +
> +static int virtio_can_start(struct net_device *ndev)
> +{
> +	struct virtio_can_priv *priv = netdev_priv(ndev);
> +	u8 result;
> +
> +	result = virtio_can_send_ctrl_msg(ndev, VIRTIO_CAN_SET_CTRL_MODE_START);
> +	if (result != VIRTIO_CAN_RESULT_OK) {
> +		netdev_err(ndev, "CAN controller start failed\n");
> +		return -EIO;
> +	}
> +
> +	priv->busoff_pending = false;
> +	priv->can.state = CAN_STATE_ERROR_ACTIVE;
> +
> +	return 0;
> +}
> +
> +static int virtio_can_set_mode(struct net_device *dev, enum can_mode mode)
> +{
> +	int err;
> +
> +	switch (mode) {
> +	case CAN_MODE_START:
> +		err = virtio_can_start(dev);
> +		if (err)
> +			return err;
> +		netif_wake_queue(dev);
> +		break;
> +	default:
> +		return -EOPNOTSUPP;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtio_can_open(struct net_device *ndev)
> +{
> +	int err;
> +
> +	err = open_candev(ndev);
> +	if (err)
> +		return err;
> +
> +	err = virtio_can_start(ndev);
> +	if (err) {
> +		close_candev(ndev);
> +		return err;
> +	}
> +
> +	netif_start_queue(ndev);
> +
> +	return 0;
> +}
> +
> +static int virtio_can_stop(struct net_device *ndev)
> +{
> +	struct virtio_can_priv *priv = netdev_priv(ndev);
> +	struct device *dev = &priv->vdev->dev;
> +	u8 result;
> +
> +	result = virtio_can_send_ctrl_msg(ndev, VIRTIO_CAN_SET_CTRL_MODE_STOP);
> +	if (result != VIRTIO_CAN_RESULT_OK) {
> +		dev_err(dev, "CAN controller stop failed\n");
> +		return -EIO;
> +	}
> +
> +	priv->busoff_pending = false;
> +	priv->can.state = CAN_STATE_STOPPED;
> +
> +	/* Switch carrier off if device was connected to the bus */
> +	if (netif_carrier_ok(ndev))
> +		netif_carrier_off(ndev);
> +
> +	return 0;
> +}
> +
> +static int virtio_can_close(struct net_device *dev)
> +{
> +	int err;
> +
> +	netif_stop_queue(dev);
> +	/* Keep RX napi active to allow dropping of pending RX CAN messages,
> +	 * keep TX napi active to allow processing of cancelled CAN messages
> +	 */
> +	err = virtio_can_stop(dev);
> +	close_candev(dev);
> +
> +	return err;
> +}
> +
> +static netdev_tx_t virtio_can_start_xmit(struct sk_buff *skb,
> +					 struct net_device *dev)
> +{
> +	struct scatterlist sg_out, sg_in, *sgs[2] = { &sg_out, &sg_in };
> +	const unsigned int hdr_size = sizeof(struct virtio_can_tx_out);
> +	struct canfd_frame *cf = (struct canfd_frame *)skb->data;
> +	struct virtio_can_priv *priv = netdev_priv(dev);
> +	struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_TX];
> +	netdev_tx_t xmit_ret = NETDEV_TX_OK;
> +	struct virtio_can_tx *can_tx_msg;
> +	u32 can_flags;
> +	int putidx;
> +	int err;
> +
> +	if (can_dev_dropped_skb(dev, skb))
> +		goto kick; /* No way to return NET_XMIT_DROP here */
> +
> +	/* No local check for CAN_RTR_FLAG or FD frame against negotiated
> +	 * features. The device will reject those anyway if not supported.
> +	 */
> +
> +	can_tx_msg = kzalloc(sizeof(*can_tx_msg) + cf->len, GFP_ATOMIC);
> +	if (!can_tx_msg) {
> +		kfree_skb(skb);
> +		dev->stats.tx_dropped++;
> +		goto kick; /* No way to return NET_XMIT_DROP here */
> +	}
> +
> +	can_tx_msg->tx_out.msg_type = cpu_to_le16(VIRTIO_CAN_TX);
> +	can_flags = 0;
> +
> +	if (cf->can_id & CAN_EFF_FLAG) {
> +		can_flags |= VIRTIO_CAN_FLAGS_EXTENDED;
> +		can_tx_msg->tx_out.can_id = cpu_to_le32(cf->can_id & CAN_EFF_MASK);
> +	} else {
> +		can_tx_msg->tx_out.can_id = cpu_to_le32(cf->can_id & CAN_SFF_MASK);
> +	}
> +	if (cf->can_id & CAN_RTR_FLAG)
> +		can_flags |= VIRTIO_CAN_FLAGS_RTR;
> +	else
> +		memcpy(can_tx_msg->tx_out.sdu, cf->data, cf->len);
> +	if (can_is_canfd_skb(skb))
> +		can_flags |= VIRTIO_CAN_FLAGS_FD;
> +
> +	can_tx_msg->tx_out.flags = cpu_to_le32(can_flags);
> +	can_tx_msg->tx_out.length = cpu_to_le16(cf->len);
> +
> +	sg_init_one(&sg_out, &can_tx_msg->tx_out, hdr_size + cf->len);
> +	sg_init_one(&sg_in, &can_tx_msg->tx_in, sizeof(can_tx_msg->tx_in));
> +
> +	putidx = virtio_can_alloc_tx_idx(priv);
> +
> +	if (unlikely(putidx < 0)) {
> +		/* -ENOMEM or -ENOSPC here. -ENOSPC should not be possible as
> +		 * tx_inflight >= can.echo_skb_max is checked in flow control
> +		 */
> +		WARN_ON_ONCE(putidx == -ENOSPC);
> +		kfree(can_tx_msg);
> +		kfree_skb(skb);
> +		dev->stats.tx_dropped++;
> +		goto kick; /* No way to return NET_XMIT_DROP here */
> +	}
> +
> +	can_tx_msg->putidx = (unsigned int)putidx;
> +
> +	/* Push loopback echo. Will be looped back on TX interrupt/TX NAPI */
> +	can_put_echo_skb(skb, dev, can_tx_msg->putidx, 0);
> +
> +	/* Protect queue and list operations */
> +	scoped_guard(spinlock_irqsave, &priv->tx_lock)
> +		err = virtqueue_add_sgs(vq, sgs, 1u, 1u, can_tx_msg, GFP_ATOMIC);
> +
> +	if (unlikely(err)) {
> +		can_free_echo_skb(dev, can_tx_msg->putidx, NULL);
> +		virtio_can_free_tx_idx(priv, can_tx_msg->putidx);
> +		netif_stop_queue(dev);
> +		kfree(can_tx_msg);
> +		/* Expected never to be seen */
> +		netdev_warn(dev, "TX: Stop queue, err = %d\n", err);
> +		xmit_ret = NETDEV_TX_BUSY;
> +		goto kick;
> +	}
> +
> +	/* Normal flow control: stop queue when no transmission slots left */
> +	if (atomic_read(&priv->tx_inflight) >= priv->can.echo_skb_max ||
> +	    vq->num_free == 0 || (vq->num_free < ARRAY_SIZE(sgs) &&
> +	    !virtio_has_feature(vq->vdev, VIRTIO_RING_F_INDIRECT_DESC))) {
> +		netif_stop_queue(dev);
> +		netdev_dbg(dev, "TX: Normal stop queue\n");
> +	}
> +
> +kick:
> +	if (netif_queue_stopped(dev) || !netdev_xmit_more()) {
> +		scoped_guard(spinlock_irqsave, &priv->tx_lock) {
> +			if (!virtqueue_kick(vq))
> +				netdev_err(dev, "%s(): Kick failed\n", __func__);
> +		}
> +	}
> +
> +	return xmit_ret;
> +}
> +
> +static const struct net_device_ops virtio_can_netdev_ops = {
> +	.ndo_open = virtio_can_open,
> +	.ndo_stop = virtio_can_close,
> +	.ndo_start_xmit = virtio_can_start_xmit,
> +};
> +
> +static int register_virtio_can_dev(struct net_device *dev)
> +{
> +	dev->flags |= IFF_ECHO;	/* we support local echo */
> +	dev->netdev_ops = &virtio_can_netdev_ops;
> +
> +	return register_candev(dev);
> +}
> +
> +static int virtio_can_read_tx_queue(struct virtqueue *vq)
> +{
> +	struct virtio_can_priv *can_priv = vq->vdev->priv;
> +	struct net_device *dev = can_priv->dev;
> +	struct virtio_can_tx *can_tx_msg;
> +	struct net_device_stats *stats;
> +	unsigned int len;
> +	u8 result;
> +
> +	stats = &dev->stats;
> +
> +	scoped_guard(spinlock_irqsave, &can_priv->tx_lock)
> +		can_tx_msg = virtqueue_get_buf(vq, &len);
> +
> +	if (!can_tx_msg)
> +		return 0;
> +
> +	if (unlikely(len < sizeof(struct virtio_can_tx_in))) {
> +		netdev_err(dev, "TX ACK: Device sent no result code\n");
> +		result = VIRTIO_CAN_RESULT_NOT_OK; /* Keep things going */
> +	} else {
> +		result = can_tx_msg->tx_in.result;
> +	}
> +
> +	if (can_priv->can.state < CAN_STATE_BUS_OFF) {
> +		if (result != VIRTIO_CAN_RESULT_OK) {
> +			struct can_frame *skb_cf;
> +			struct sk_buff *skb = alloc_can_err_skb(dev, &skb_cf);
> +
> +			if (skb) {
> +				skb_cf->can_id |= CAN_ERR_CRTL;
> +				skb_cf->data[1] |= CAN_ERR_CRTL_UNSPEC;
> +				netif_rx(skb);
> +			}
> +			netdev_warn(dev, "TX ACK: Result = %u\n", result);
> +			can_free_echo_skb(dev, can_tx_msg->putidx, NULL);
> +			stats->tx_dropped++;
> +		} else {
> +			stats->tx_bytes += can_get_echo_skb(dev, can_tx_msg->putidx,
> +				NULL);
> +			stats->tx_packets++;
> +		}
> +	} else {
> +		netdev_dbg(dev, "TX ACK: Controller inactive, drop echo\n");
> +		can_free_echo_skb(dev, can_tx_msg->putidx, NULL);
> +		stats->tx_dropped++;
> +	}
> +
> +	virtio_can_free_tx_idx(can_priv, can_tx_msg->putidx);
> +
> +	/* Flow control */
> +	if (netif_queue_stopped(dev)) {
> +		netdev_dbg(dev, "TX ACK: Wake up stopped queue\n");
> +		netif_wake_queue(dev);
> +	}
> +
> +	kfree(can_tx_msg);
> +
> +	return 1; /* Queue was not empty so there may be more data */
> +}
> +
> +static int virtio_can_tx_poll(struct napi_struct *napi, int quota)
> +{
> +	struct net_device *dev = napi->dev;
> +	struct virtio_can_priv *priv = netdev_priv(dev);
> +	struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_TX];
> +	int work_done = 0;
> +
> +	while (work_done < quota && virtio_can_read_tx_queue(vq) != 0)
> +		work_done++;
> +
> +	if (work_done < quota)
> +		virtqueue_napi_complete(napi, vq, work_done);
> +
> +	return work_done;
> +}
> +
> +static void virtio_can_tx_intr(struct virtqueue *vq)
> +{
> +	struct virtio_can_priv *can_priv = vq->vdev->priv;
> +
> +	virtqueue_disable_cb(vq);
> +	napi_schedule(&can_priv->napi_tx);
> +}
> +
> +/* This function is the NAPI RX poll function and NAPI guarantees that this
> + * function is not invoked simultaneously on multiple processors.
> + * Read a RX message from the used queue and sends it to the upper layer.
> + */
> +static int virtio_can_read_rx_queue(struct virtqueue *vq)
> +{
> +	const unsigned int header_size = sizeof(struct virtio_can_rx);
> +	struct virtio_can_priv *priv = vq->vdev->priv;
> +	struct net_device *dev = priv->dev;
> +	struct net_device_stats *stats;
> +	struct virtio_can_rx *can_rx;
> +	unsigned int transport_len;
> +	struct canfd_frame *cf;
> +	struct sk_buff *skb;
> +	unsigned int len;
> +	u32 can_flags;
> +	u16 msg_type;
> +	u32 can_id;
> +	int ret;
> +
> +	stats = &dev->stats;
> +
> +	can_rx = virtqueue_get_buf(vq, &transport_len);
> +	if (!can_rx)
> +		return 0; /* No more data */
> +
> +	if (transport_len < header_size) {
> +		netdev_warn(dev, "RX: Message too small\n");
> +		goto putback;
> +	}
> +
> +	if (priv->can.state >= CAN_STATE_ERROR_PASSIVE) {
> +		netdev_dbg(dev, "%s(): Controller not active\n", __func__);
> +		goto putback;
> +	}
> +
> +	msg_type = le16_to_cpu(can_rx->msg_type);
> +	if (msg_type != VIRTIO_CAN_RX) {
> +		netdev_warn(dev, "RX: Got unknown msg_type %04x\n", msg_type);
> +		goto putback;
> +	}
> +
> +	len = le16_to_cpu(can_rx->length);
> +	can_flags = le32_to_cpu(can_rx->flags);
> +	can_id = le32_to_cpu(can_rx->can_id);
> +
> +	if (can_flags & ~CAN_KNOWN_FLAGS) {
> +		stats->rx_dropped++;
> +		netdev_warn(dev, "RX: CAN Id 0x%08x: Invalid flags 0x%x\n",
> +			    can_id, can_flags);
> +		goto putback;
> +	}
> +
> +	if (can_flags & VIRTIO_CAN_FLAGS_EXTENDED) {
> +		can_id &= CAN_EFF_MASK;
> +		can_id |= CAN_EFF_FLAG;
> +	} else {
> +		can_id &= CAN_SFF_MASK;
> +	}
> +
> +	if (can_flags & VIRTIO_CAN_FLAGS_RTR) {
> +		if (!virtio_has_feature(vq->vdev, VIRTIO_CAN_F_RTR_FRAMES)) {
> +			stats->rx_dropped++;
> +			netdev_warn(dev, "RX: CAN Id 0x%08x: RTR not negotiated\n",
> +				    can_id);
> +			goto putback;
> +		}
> +		if (can_flags & VIRTIO_CAN_FLAGS_FD) {
> +			stats->rx_dropped++;
> +			netdev_warn(dev, "RX: CAN Id 0x%08x: RTR with FD not possible\n",
> +				    can_id);
> +			goto putback;
> +		}
> +
> +		if (len > 0xF) {
> +			stats->rx_dropped++;
> +			netdev_warn(dev, "RX: CAN Id 0x%08x: RTR with DLC > 0xF\n",
> +				    can_id);
> +			goto putback;
> +		}
> +
> +		if (len > 0x8)
> +			len = 0x8;
> +
> +		can_id |= CAN_RTR_FLAG;
> +	}
> +
> +	if (transport_len < header_size + len) {
> +		netdev_warn(dev, "RX: Message too small for payload\n");
> +		goto putback;
> +	}
> +
> +	if (can_flags & VIRTIO_CAN_FLAGS_FD) {
> +		if (!virtio_has_feature(vq->vdev, VIRTIO_CAN_F_CAN_FD)) {
> +			stats->rx_dropped++;
> +			netdev_warn(dev, "RX: CAN Id 0x%08x: FD not negotiated\n",
> +				    can_id);
> +			goto putback;
> +		}
> +
> +		if (len > CANFD_MAX_DLEN)
> +			len = CANFD_MAX_DLEN;
> +
> +		skb = alloc_canfd_skb(priv->dev, &cf);
> +	} else {
> +		if (!virtio_has_feature(vq->vdev, VIRTIO_CAN_F_CAN_CLASSIC)) {
> +			stats->rx_dropped++;
> +			netdev_warn(dev, "RX: CAN Id 0x%08x: classic not negotiated\n",
> +				    can_id);
> +			goto putback;
> +		}
> +
> +		if (len > CAN_MAX_DLEN)
> +			len = CAN_MAX_DLEN;
> +
> +		skb = alloc_can_skb(priv->dev, (struct can_frame **)&cf);
> +	}
> +	if (!skb) {
> +		stats->rx_dropped++;
> +		netdev_warn(dev, "RX: No skb available\n");
> +		goto putback;
> +	}
> +
> +	cf->can_id = can_id;
> +	cf->len = len;
> +	if (!(can_flags & VIRTIO_CAN_FLAGS_RTR)) {
> +		/* RTR frames have a DLC but no payload */
> +		memcpy(cf->data, can_rx->sdu, len);
> +	}
> +
> +	if (netif_receive_skb(skb) == NET_RX_SUCCESS) {
> +		stats->rx_packets++;
> +		if (!(can_flags & VIRTIO_CAN_FLAGS_RTR))
> +			stats->rx_bytes += cf->len;
> +	}
> +
> +putback:
> +	/* Put processed RX buffer back into avail queue */
> +	ret = virtio_can_add_inbuf(vq, can_rx,
> +				   priv->rpkt_len);
> +	if (!ret)
> +		virtqueue_kick(vq);
> +	return 1; /* Queue was not empty so there may be more data */
> +}
> +
> +static int virtio_can_handle_busoff(struct net_device *dev)
> +{
> +	struct virtio_can_priv *priv = netdev_priv(dev);
> +	struct can_frame *cf;
> +	struct sk_buff *skb;
> +
> +	if (!priv->busoff_pending)
> +		return 0;
> +
> +	if (priv->can.state < CAN_STATE_BUS_OFF) {
> +		netdev_dbg(dev, "entered error bus off state\n");
> +
> +		/* bus-off state */
> +		priv->can.state = CAN_STATE_BUS_OFF;
> +		priv->can.can_stats.bus_off++;
> +		can_bus_off(dev);
> +	}
> +
> +	/* propagate the error condition to the CAN stack */
> +	skb = alloc_can_err_skb(dev, &cf);
> +	if (unlikely(!skb))
> +		return 0;
> +
> +	/* bus-off state */
> +	cf->can_id |= CAN_ERR_BUSOFF;
> +
> +	/* Ensure that the BusOff indication does not get lost */
> +	if (netif_receive_skb(skb) == NET_RX_SUCCESS)
> +		priv->busoff_pending = false;
> +
> +	return 1;
> +}
> +
> +static int virtio_can_rx_poll(struct napi_struct *napi, int quota)
> +{
> +	struct net_device *dev = napi->dev;
> +	struct virtio_can_priv *priv = netdev_priv(dev);
> +	struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_RX];
> +	int work_done = 0;
> +
> +	work_done += virtio_can_handle_busoff(dev);
> +
> +	while (work_done < quota && virtio_can_read_rx_queue(vq) != 0)
> +		work_done++;
> +
> +	if (work_done < quota)
> +		virtqueue_napi_complete(napi, vq, work_done);
> +
> +	return work_done;
> +}
> +
> +static void virtio_can_rx_intr(struct virtqueue *vq)
> +{
> +	struct virtio_can_priv *can_priv = vq->vdev->priv;
> +
> +	virtqueue_disable_cb(vq);
> +	napi_schedule(&can_priv->napi);
> +}
> +
> +static void virtio_can_control_intr(struct virtqueue *vq)
> +{
> +	struct virtio_can_priv *can_priv = vq->vdev->priv;
> +
> +	complete(&can_priv->ctrl_done);
> +}
> +
> +static void virtio_can_config_changed(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *can_priv = vdev->priv;
> +	u16 status;
> +
> +	status = virtio_cread16(vdev, offsetof(struct virtio_can_config,
> +					       status));
> +
> +	if (!(status & VIRTIO_CAN_S_CTRL_BUSOFF))
> +		return;
> +
> +	if (!can_priv->busoff_pending &&
> +	    can_priv->can.state < CAN_STATE_BUS_OFF) {
> +		can_priv->busoff_pending = true;
> +		napi_schedule(&can_priv->napi);
> +	}
> +}
> +
> +static void virtio_can_populate_rx_vq(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv = vdev->priv;
> +	struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_RX];
> +	unsigned int buf_size = priv->rpkt_len;
> +	int num_elements = vq->num_free;
> +	u8 *buf = (u8 *)priv->rpkt;
> +	unsigned int idx;
> +	int ret = 0;
> +
> +	for (idx = 0; idx < num_elements; idx++) {
> +		ret = virtio_can_add_inbuf(vq, buf, buf_size);
> +		if (ret < 0) {
> +			dev_dbg(&vdev->dev, "rpkt fill: ret=%d, idx=%u, size=%u\n",
> +				ret, idx, buf_size);
> +			break;
> +		}
> +		buf += buf_size;
> +	}
> +
> +	if (!ret)
> +		virtqueue_kick(vq);
> +
> +	dev_dbg(&vdev->dev, "%u rpkt added\n", idx);
> +}
> +
> +static int virtio_can_find_vqs(struct virtio_can_priv *priv)
> +{
> +	struct virtqueue_info vqs_info[] = {
> +		{ "can-tx", virtio_can_tx_intr },
> +		{ "can-rx", virtio_can_rx_intr },
> +		{ "can-state-ctrl", virtio_can_control_intr },
> +	};
> +
> +	/* Find the queues. */
> +	return virtio_find_vqs(priv->vdev, VIRTIO_CAN_QUEUE_COUNT, priv->vqs,
> +			       vqs_info, NULL);
> +}
> +
> +/* Function must not be called before virtio_can_find_vqs() has been run */
> +static void virtio_can_del_vq(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv = vdev->priv;
> +	int q;
> +
> +	/* Reset the device */
> +	virtio_reset_device(vdev);
> +
> +	/* From here we have dead silence from the device side so no locks
> +	 * are needed to protect against device side events.
> +	 */
> +
> +	for (q = 0; q < VIRTIO_CAN_QUEUE_COUNT; q++)
> +		while (virtqueue_detach_unused_buf(priv->vqs[q]))
> +			;
> +
> +	if (vdev->config->del_vqs)
> +		vdev->config->del_vqs(vdev);
> +}
> +
> +static void virtio_can_remove(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv = vdev->priv;
> +	struct net_device *dev = priv->dev;
> +
> +	napi_disable(&priv->napi);
> +	napi_disable(&priv->napi_tx);
> +
> +	unregister_candev(dev);
> +
> +	virtio_can_del_vq(vdev);
> +
> +	virtio_can_free_candev(dev);
> +}
> +
> +static int virtio_can_validate(struct virtio_device *vdev)
> +{
> +	/* CAN needs always access to the config space.
> +	 * Check that the driver can access the config space
> +	 */
> +	if (!vdev->config->get) {
> +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> +			__func__);
> +		return -EINVAL;
> +	}
> +
> +	if (!virtio_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> +		dev_err(&vdev->dev,
> +			"device does not comply with spec version 1.x\n");
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int virtio_can_probe(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv;
> +	struct net_device *dev;
> +	int err;
> +
> +	dev = alloc_candev(sizeof(struct virtio_can_priv),
> +			   VIRTIO_CAN_ECHO_SKB_MAX);
> +	if (!dev)
> +		return -ENOMEM;
> +
> +	priv = netdev_priv(dev);
> +
> +	ida_init(&priv->tx_putidx_ida);
> +
> +	netif_napi_add(dev, &priv->napi, virtio_can_rx_poll);
> +	netif_napi_add(dev, &priv->napi_tx, virtio_can_tx_poll);
> +
> +	SET_NETDEV_DEV(dev, &vdev->dev);
> +
> +	priv->dev = dev;
> +	priv->vdev = vdev;
> +	vdev->priv = priv;
> +
> +	priv->can.do_set_mode = virtio_can_set_mode;
> +	priv->can.bittiming.bitrate = CAN_BITRATE_UNKNOWN;
> +	/* Set Virtio CAN supported operations */
> +	priv->can.ctrlmode_supported = CAN_CTRLMODE_BERR_REPORTING;
> +	if (virtio_has_feature(vdev, VIRTIO_CAN_F_CAN_FD)) {
> +		priv->can.fd.data_bittiming.bitrate = CAN_BITRATE_UNKNOWN;
> +		err = can_set_static_ctrlmode(dev, CAN_CTRLMODE_FD);
> +		if (err != 0)
> +			goto on_failure;
> +	}
> +
> +	/* Initialize virtqueues */
> +	err = virtio_can_find_vqs(priv);
> +	if (err != 0)
> +		goto on_failure;
> +
> +	spin_lock_init(&priv->tx_lock);
> +	mutex_init(&priv->ctrl_lock);
> +
> +	init_completion(&priv->ctrl_done);
> +
> +	priv->rpkt_len = sizeof(struct virtio_can_rx);
> +
> +	if (virtio_has_feature(vdev, VIRTIO_CAN_F_CAN_FD))
> +		priv->rpkt_len += CANFD_MAX_DLEN;
> +	else
> +		priv->rpkt_len += CAN_MAX_DLEN;
> +
> +	priv->rpkt = devm_kzalloc(&vdev->dev, priv->rpkt_len *
> +						priv->vqs[VIRTIO_CAN_QUEUE_RX]->num_free,
> +						GFP_KERNEL);
> +	if (!priv->rpkt) {
> +		virtio_can_del_vq(vdev);
> +		err = -ENOMEM;
> +		goto on_failure;
> +	}
> +	virtio_can_populate_rx_vq(vdev);
> +
> +	err = register_virtio_can_dev(dev);
> +	if (err) {
> +		virtio_can_del_vq(vdev);
> +		goto on_failure;
> +	}
> +
> +	napi_enable(&priv->napi);
> +	napi_enable(&priv->napi_tx);
> +
> +	return 0;
> +
> +on_failure:
> +	virtio_can_free_candev(dev);
> +	return err;
> +}
> +
> +static int __maybe_unused virtio_can_freeze(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv = vdev->priv;
> +	struct net_device *ndev = priv->dev;
> +
> +	napi_disable(&priv->napi);
> +	napi_disable(&priv->napi_tx);
> +
> +	if (netif_running(ndev)) {
> +		int err;
> +
> +		netif_stop_queue(ndev);
> +		netif_device_detach(ndev);
> +		err = virtio_can_stop(ndev);
> +		if (err)
> +			return err;
> +	}
> +
> +	priv->can.state = CAN_STATE_SLEEPING;
> +
> +	virtio_can_del_vq(vdev);
> +
> +	return 0;
> +}
> +
> +static int __maybe_unused virtio_can_restore(struct virtio_device *vdev)
> +{
> +	struct virtio_can_priv *priv = vdev->priv;
> +	struct net_device *ndev = priv->dev;
> +	int err;
> +
> +	err = virtio_can_find_vqs(priv);
> +	if (err != 0)
> +		return err;
> +	virtio_can_populate_rx_vq(vdev);
> +
> +	priv->can.state = CAN_STATE_ERROR_ACTIVE;
> +
> +	if (netif_running(ndev)) {
> +		virtio_can_start(ndev);
> +		netif_device_attach(ndev);
> +		netif_start_queue(ndev);
> +	}
> +
> +	napi_enable(&priv->napi);
> +	napi_enable(&priv->napi_tx);
> +
> +	return 0;
> +}
> +
> +static struct virtio_device_id virtio_can_id_table[] = {
> +	{ VIRTIO_ID_CAN, VIRTIO_DEV_ANY_ID },
> +	{ 0 },
> +};
> +
> +static unsigned int features[] = {
> +	VIRTIO_CAN_F_CAN_CLASSIC,
> +	VIRTIO_CAN_F_CAN_FD,
> +	VIRTIO_CAN_F_LATE_TX_ACK,
> +	VIRTIO_CAN_F_RTR_FRAMES,
> +};
> +
> +static struct virtio_driver virtio_can_driver = {
> +	.feature_table = features,
> +	.feature_table_size = ARRAY_SIZE(features),
> +	.driver.name = KBUILD_MODNAME,
> +	.driver.owner = THIS_MODULE,
> +	.id_table = virtio_can_id_table,
> +	.validate = virtio_can_validate,
> +	.probe = virtio_can_probe,
> +	.remove = virtio_can_remove,
> +	.config_changed = virtio_can_config_changed,
> +#ifdef CONFIG_PM_SLEEP
> +	.freeze = virtio_can_freeze,
> +	.restore = virtio_can_restore,
> +#endif
> +};
> +
> +module_virtio_driver(virtio_can_driver);
> +MODULE_DEVICE_TABLE(virtio, virtio_can_id_table);
> +
> +MODULE_AUTHOR("OpenSynergy GmbH");
> +MODULE_LICENSE("GPL");
> +MODULE_DESCRIPTION("CAN bus driver for Virtio CAN controller");
> diff --git a/include/uapi/linux/virtio_can.h b/include/uapi/linux/virtio_can.h
> new file mode 100644
> index 000000000000..ade068188d22
> --- /dev/null
> +++ b/include/uapi/linux/virtio_can.h
> @@ -0,0 +1,78 @@
> +/* SPDX-License-Identifier: BSD-3-Clause */
> +/*
> + * Copyright (C) 2021-2023 OpenSynergy GmbH
> + * Copyright Red Hat, Inc. 2025
> + */
> +#ifndef _LINUX_VIRTIO_VIRTIO_CAN_H
> +#define _LINUX_VIRTIO_VIRTIO_CAN_H
> +
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +#include <linux/virtio_ids.h>
> +#include <linux/virtio_config.h>
> +
> +/* Feature bit numbers */
> +#define VIRTIO_CAN_F_CAN_CLASSIC        0
> +#define VIRTIO_CAN_F_CAN_FD             1
> +#define VIRTIO_CAN_F_RTR_FRAMES         2
> +#define VIRTIO_CAN_F_LATE_TX_ACK        3
> +
> +/* CAN Result Types */
> +#define VIRTIO_CAN_RESULT_OK            0
> +#define VIRTIO_CAN_RESULT_NOT_OK        1
> +
> +/* CAN flags to determine type of CAN Id */
> +#define VIRTIO_CAN_FLAGS_EXTENDED       0x8000
> +#define VIRTIO_CAN_FLAGS_FD             0x4000
> +#define VIRTIO_CAN_FLAGS_RTR            0x2000
> +
> +#define VIRTIO_CAN_MAX_DLEN    64 // this is like CANFD_MAX_DLEN
> +
> +struct virtio_can_config {
> +#define VIRTIO_CAN_S_CTRL_BUSOFF (1u << 0) /* Controller BusOff */
> +	/* CAN controller status */
> +	__le16 status;
> +};
> +
> +/* TX queue message types */
> +struct virtio_can_tx_out {
> +#define VIRTIO_CAN_TX                   0x0001
> +	__le16 msg_type;
> +	__le16 length; /* 0..8 CC, 0..64 CAN-FD, 0..2048 CAN-XL, 12 bits */
> +	__u8 reserved_classic_dlc; /* If CAN classic length = 8 then DLC can be 8..15 */
> +	__u8 padding;
> +	__le16 reserved_xl_priority; /* May be needed for CAN XL priority */
> +	__le32 flags;
> +	__le32 can_id;
> +	__u8 sdu[] __counted_by(length);
> +};
> +
> +struct virtio_can_tx_in {
> +	__u8 result;
> +};
> +
> +/* RX queue message types */
> +struct virtio_can_rx {
> +#define VIRTIO_CAN_RX                   0x0101
> +	__le16 msg_type;
> +	__le16 length; /* 0..8 CC, 0..64 CAN-FD, 0..2048 CAN-XL, 12 bits */
> +	__u8 reserved_classic_dlc; /* If CAN classic length = 8 then DLC can be 8..15 */
> +	__u8 padding;
> +	__le16 reserved_xl_priority; /* May be needed for CAN XL priority */
> +	__le32 flags;
> +	__le32 can_id;
> +	__u8 sdu[] __counted_by(length);
> +};
> +
> +/* Control queue message types */
> +struct virtio_can_control_out {
> +#define VIRTIO_CAN_SET_CTRL_MODE_START  0x0201
> +#define VIRTIO_CAN_SET_CTRL_MODE_STOP   0x0202
> +	__le16 msg_type;
> +};
> +
> +struct virtio_can_control_in {
> +	__u8 result;
> +};
> +
> +#endif /* #ifndef _LINUX_VIRTIO_VIRTIO_CAN_H */
> -- 
> 2.42.0
>