On Thu, Sep 11, 2025 at 10:59:40PM +0200, Francesco Valla wrote: > Hello Mikhail, Harald, > > hoping there will be a v6 of this patch soon, a few comments: >
I am working on the v6 by addressing the comments in this thread. > On Monday, 8 January 2024 at 14:10:35 Mikhail Golubev-Ciuchea > <[email protected]> wrote: > > [...] > > > + > > +/* 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]; > > + /* I/O callback function pointers for the virtqueues */ > > + vq_callback_t *io_callbacks[VIRTIO_CAN_QUEUE_COUNT]; > > + /* Lock for TX operations */ > > + spinlock_t tx_lock; > > + /* Control queue lock. Defensive programming, may be not needed */ > > + struct mutex ctrl_lock; > > + /* Wait for control queue processing without polling */ > > + struct completion ctrl_done; > > + /* List of virtio CAN TX message */ > > + struct list_head tx_list; > > + /* Array of receive queue messages */ > > + struct virtio_can_rx rpkt[128]; > > This array should probably be allocated dynamically at probe - maybe > using a module parameter instead of a hardcoded value as length? > If I allocate this array in probe(), I would not know sdu[] in advance if I defined it as a flexible array. That made me wonder: can sdu[] be defined as flexible array for rx? Thanks. > > + /* Those control queue messages cannot live on the stack! */ > > + struct virtio_can_control_out cpkt_out; > > + struct virtio_can_control_in cpkt_in; > > Consider using a container struct as you did for the tx message, e.g.: > > struct virtio_can_control { > struct virtio_can_control_out ctrl_out; > struct virtio_can_control_in ctrl_in; > }; > > > + /* Data to get and maintain the putidx for local TX echo */ > > + struct ida tx_putidx_ida; > > + /* In flight TX messages */ > > + atomic_t tx_inflight; > > + /* BusOff pending. Reset after successful indication to upper layer */ > > + bool busoff_pending; > > +}; > > + > > [...] > > > + > > +/* Send a control message with message type either > > + * > > + * - VIRTIO_CAN_SET_CTRL_MODE_START or > > + * - VIRTIO_CAN_SET_CTRL_MODE_STOP. > > + * > > + * Unlike AUTOSAR CAN Driver Can_SetControllerMode() there is no > > requirement > > + * for this Linux driver to have an asynchronous implementation of the mode > > + * setting function so in order to keep things simple the function is > > + * implemented as synchronous function. Design pattern is > > + * virtio_console.c/__send_control_msg() & > > virtio_net.c/virtnet_send_command(). > > + */ > > +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 device *dev = &priv->vdev->dev; > > + struct virtqueue *vq; > > + unsigned int len; > > + int err; > > + > > + vq = priv->vqs[VIRTIO_CAN_QUEUE_CONTROL]; > > + > > + /* The function may be serialized by rtnl lock. Not sure. > > + * Better safe than sorry. > > + */ > > + mutex_lock(&priv->ctrl_lock); > > + > > + priv->cpkt_out.msg_type = cpu_to_le16(msg_type); > > + sg_init_one(&sg_out, &priv->cpkt_out, sizeof(priv->cpkt_out)); > > + sg_init_one(&sg_in, &priv->cpkt_in, sizeof(priv->cpkt_in)); > > + > > + err = virtqueue_add_sgs(vq, sgs, 1u, 1u, priv, GFP_ATOMIC); > > + if (err != 0) { > > + /* Not expected to happen */ > > + dev_err(dev, "%s(): virtqueue_add_sgs() failed\n", __func__); > > + } > > Here it should return VIRTIO_CAN_RESULT_NOT_OK after unlocking the > mutex, or it might wait for completion indefinitley below. > > > + > > + if (!virtqueue_kick(vq)) { > > + /* Not expected to happen */ > > + dev_err(dev, "%s(): Kick failed\n", __func__); > > + } > > And here too. > > > + > > + while (!virtqueue_get_buf(vq, &len) && !virtqueue_is_broken(vq)) > > + wait_for_completion(&priv->ctrl_done); > > + > > + mutex_unlock(&priv->ctrl_lock); > > + > > + return priv->cpkt_in.result; > > +} > > + > > [...] > > > +static netdev_tx_t virtio_can_start_xmit(struct sk_buff *skb, > > + struct net_device *dev) > > +{ > > + const unsigned int hdr_size = offsetof(struct virtio_can_tx_out, sdu); > > + struct scatterlist sg_out, sg_in, *sgs[2] = { &sg_out, &sg_in }; > > + struct canfd_frame *cf = (struct canfd_frame *)skb->data; > > + struct virtio_can_priv *priv = netdev_priv(dev); > > + netdev_tx_t xmit_ret = NETDEV_TX_OK; > > + struct virtio_can_tx *can_tx_msg; > > + struct virtqueue *vq; > > + unsigned long flags; > > + u32 can_flags; > > + int putidx; > > + int err; > > + > > + vq = priv->vqs[VIRTIO_CAN_QUEUE_TX]; > > + > > + 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), GFP_ATOMIC); > > + if (!can_tx_msg) { > > + dev->stats.tx_dropped++; > > + goto kick; /* No way to return NET_XMIT_DROP here */ > > + } > > + > > Since we are allocating tx messages dynamically, the sdu[64] array inside > struct virtio_can_tx_out can be converted to a flexible array and here > the allocation can become: > > can_tx_msg = kzalloc(sizeof(*can_tx_msg) + cf->len, GFP_ATOMIC); > > This would save memory in particular on CAN-CC interfaces, where 56 bytes > per message would otherwise be lost (not to mention the case if/when > CAN-XL will be supported). > > > + 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); > > + > > + /* Prepare sending of virtio message */ > > + 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); > > + dev->stats.tx_dropped++; > > + goto kick; /* No way to return NET_XMIT_DROP here */ > > + } > > + > > + can_tx_msg->putidx = (unsigned int)putidx; > > + > > + /* Protect list operation */ > > + spin_lock_irqsave(&priv->tx_lock, flags); > > + list_add_tail(&can_tx_msg->list, &priv->tx_list); > > + spin_unlock_irqrestore(&priv->tx_lock, flags); > > + > > + /* 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 */ > > + spin_lock_irqsave(&priv->tx_lock, flags); > > + err = virtqueue_add_sgs(vq, sgs, 1u, 1u, can_tx_msg, GFP_ATOMIC); > > + if (unlikely(err)) { /* checking vq->num_free in flow control */ > > + list_del(&can_tx_msg->list); > > + can_free_echo_skb(dev, can_tx_msg->putidx, NULL); > > + virtio_can_free_tx_idx(priv, can_tx_msg->putidx); > > + spin_unlock_irqrestore(&priv->tx_lock, flags); > > + 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"); > > + } > > + > > + spin_unlock_irqrestore(&priv->tx_lock, flags); > > + > > +kick: > > + if (netif_queue_stopped(dev) || !netdev_xmit_more()) { > > + 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, > > + .ndo_change_mtu = can_change_mtu, > > +}; > > + > > +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); > > +} > > + > > +/* Compare with m_can.c/m_can_echo_tx_event() */ > > +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 long flags; > > + unsigned int len; > > + u8 result; > > + > > + stats = &dev->stats; > > + > > + /* Protect list and virtio queue operations */ > > + spin_lock_irqsave(&can_priv->tx_lock, flags); > > + > > + can_tx_msg = virtqueue_get_buf(vq, &len); > > + if (!can_tx_msg) { > > + spin_unlock_irqrestore(&can_priv->tx_lock, flags); > > + return 0; /* No more data */ > > + } > > + > > + 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) { > > + /* Here also frames with result != VIRTIO_CAN_RESULT_OK are > > + * echoed. Intentional to bring a waiting process in an upper > > + * layer to an end. > > + * TODO: Any better means to indicate a problem here? > > + */ > > + if (result != VIRTIO_CAN_RESULT_OK) > > + netdev_warn(dev, "TX ACK: Result = %u\n", result); > > Maybe an error frame reporting CAN_ERR_CRTL_UNSPEC would be better? > > For sure, counting the known errors as valid tx_packets and tx_bytes > is misleading. > > > + > > + 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); > > + } > > + > > + list_del(&can_tx_msg->list); > > + 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); > > + } > > + > > + spin_unlock_irqrestore(&can_priv->tx_lock, flags); > > + > > + kfree(can_tx_msg); > > + > > + return 1; /* Queue was not empty so there may be more data */ > > +} > > + > > [...] > > > + > > +static int virtio_can_find_vqs(struct virtio_can_priv *priv) > > +{ > > + /* The order of RX and TX is exactly the opposite as in console and > > + * network. Does not play any role but is a bad trap. > > + */ > > + static const char * const io_names[VIRTIO_CAN_QUEUE_COUNT] = { > > + "can-tx", > > + "can-rx", > > + "can-state-ctrl" > > + }; > > + > > + priv->io_callbacks[VIRTIO_CAN_QUEUE_TX] = virtio_can_tx_intr; > > + priv->io_callbacks[VIRTIO_CAN_QUEUE_RX] = virtio_can_rx_intr; > > + priv->io_callbacks[VIRTIO_CAN_QUEUE_CONTROL] = virtio_can_control_intr; > > + > > + /* Find the queues. */ > > + return virtio_find_vqs(priv->vdev, VIRTIO_CAN_QUEUE_COUNT, priv->vqs, > > + priv->io_callbacks, io_names, NULL); > > +} > > Syntax of virtio_find_vqs changed a bit, here should now be: > > struct virtqueue_info vqs_info[] = { > { "can-tx", virtio_can_tx_intr }, > { "can-rx", virtio_can_rx_intr }, > { "can-state-ctrl", virtio_can_control_intr }, > }; > > 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; > > + struct list_head *cursor, *next; > > + struct virtqueue *vq; > > + > > + /* Reset the device */ > > + if (vdev->config->reset) > > + vdev->config->reset(vdev); > > + > > + /* From here we have dead silence from the device side so no locks > > + * are needed to protect against device side events. > > + */ > > + > > + vq = priv->vqs[VIRTIO_CAN_QUEUE_CONTROL]; > > + while (virtqueue_detach_unused_buf(vq)) > > + ; /* Do nothing, content allocated statically */ > > + > > + vq = priv->vqs[VIRTIO_CAN_QUEUE_RX]; > > + while (virtqueue_detach_unused_buf(vq)) > > + ; /* Do nothing, content allocated statically */ > > + > > + vq = priv->vqs[VIRTIO_CAN_QUEUE_TX]; > > + while (virtqueue_detach_unused_buf(vq)) > > + ; /* Do nothing, content to be de-allocated separately */ > > + > > + /* Is keeping track of allocated elements by an own linked list > > + * really necessary or may this be optimized using only > > + * virtqueue_detach_unused_buf()? > > + */ > > + list_for_each_safe(cursor, next, &priv->tx_list) { > > + struct virtio_can_tx *can_tx; > > + > > + can_tx = list_entry(cursor, struct virtio_can_tx, list); > > + list_del(cursor); > > + kfree(can_tx); > > + } > > I'd drop the tx_list entirely and rely on virtqueue_detach_unused_buf(); > this would allow to remove at least one spinlock save/restore pair at > each transmission. > > > + > > + if (vdev->config->del_vqs) > > + vdev->config->del_vqs(vdev); > > +} > > + > > [...] > > > diff --git a/include/uapi/linux/virtio_can.h > > b/include/uapi/linux/virtio_can.h > > new file mode 100644 > > index 000000000000..7cf613bb3f1a > > --- /dev/null > > +++ b/include/uapi/linux/virtio_can.h > > @@ -0,0 +1,75 @@ > > +/* SPDX-License-Identifier: BSD-3-Clause */ > > +/* > > + * Copyright (C) 2021-2023 OpenSynergy GmbH > > + */ > > +#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_LATE_TX_ACK 2 > > +#define VIRTIO_CAN_F_RTR_FRAMES 3 > > + > > The values for VIRTIO_CAN_F_LATE_TX_ACK and VIRTIO_CAN_F_RTR_FRAMES are > inverted w.r.t. the merged virto-can spec [1]. > > Note that this is the only deviation from the spec I found. > > > +/* 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 > > + > > +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[64]; > > +}; > > + > > sdu[] here might be a flexible array, if the driver allocates > virtio_can_tx_out structs dyncamically (see above). This would be > beneficial in case of CAN-XL frames (if/when they will be supported). > > > +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[64]; > > +}; > > + > > Again, sdu[] might be a flexible array. > > > +/* 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 */ > > > > Thank you for your work! > > Regards, > Francesco > > > [1] > https://github.com/oasis-tcs/virtio-spec/blob/virtio-1.4/device-types/can/description.tex#L45 > > > >
