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Subject: Re: [RFC PATCH v3] can: virtio: Initial virtio CAN driver.
On 11.05.23 17:40, Simon Horman wrote:
On Thu, May 11, 2023 at 05:14:44PM +0200, Mikhail Golubev-Ciuchea wrote:From: Harald Mommer<harald.mommer@opensynergy.com> - CAN Control - "ip link set up can0" starts the virtual CAN controller, - "ip link set up can0" stops the virtual CAN controller - CAN RX Receive CAN frames. CAN frames can be standard or extended, classic or CAN FD. Classic CAN RTR frames are supported. - CAN TX Send CAN frames. CAN frames can be standard or extended, classic or CAN FD. Classic CAN RTR frames are supported. - CAN BusOff indication CAN BusOff is handled by a bit in the configuration space. Signed-off-by: Harald Mommer<Harald.Mommer@opensynergy.com> Signed-off-by: Mikhail Golubev-Ciuchea<Mikhail.Golubev-Ciuchea@opensynergy.com> Co-developed-by: Marc Kleine-Budde<mkl@pengutronix.de> Signed-off-by: Marc Kleine-Budde<mkl@pengutronix.de> Cc: Damir Shaikhutdinov<Damir.Shaikhutdinov@opensynergy.com>Hi Mikhail, thanks for your patch. Some minor feedback from my side. ...diff --git a/drivers/net/can/virtio_can.c b/drivers/net/can/virtio_can.c...+/* 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 virtio_can_priv *priv = netdev_priv(ndev); + struct device *dev = &priv->vdev->dev; + struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_CONTROL]; + struct scatterlist sg_out[1]; + struct scatterlist sg_in[1]; + struct scatterlist *sgs[2]; + int err; + unsigned int len;nit: For networking code please arrange local variables in reverse xmas tree order - longest line to shortest. You can check this using:https://github.com/ecree-solarflare/xmastree In this case I think it would be: struct virtio_can_priv *priv = netdev_priv(ndev); struct device *dev = &priv->vdev->dev; struct scatterlist sg_out[1]; struct scatterlist sg_in[1]; struct scatterlist *sgs[2]; struct virtqueue *vq; unsigned int len; int err; vq = priv->vqs[VIRTIO_CAN_QUEUE_CONTROL]; ...
https://docs.kernel.org/process/maintainer-netdev.html I see, I see...
+static netdev_tx_t virtio_can_start_xmit(struct sk_buff *skb, + struct net_device *dev) +{ + struct virtio_can_priv *priv = netdev_priv(dev); + struct canfd_frame *cf = (struct canfd_frame *)skb->data; + struct virtio_can_tx *can_tx_msg; + struct virtqueue *vq = priv->vqs[VIRTIO_CAN_QUEUE_TX]; + struct scatterlist sg_out[1]; + struct scatterlist sg_in[1]; + struct scatterlist *sgs[2]; + unsigned long flags; + u32 can_flags; + int err; + int putidx; + netdev_tx_t xmit_ret = NETDEV_TX_OK; + const unsigned int hdr_size = offsetof(struct virtio_can_tx_out, sdu); + + 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) + 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); + + /* Prepare sending of virtio message */ + sg_init_one(&sg_out[0], &can_tx_msg->tx_out, hdr_size + cf->len); + sg_init_one(&sg_in[0], &can_tx_msg->tx_in, sizeof(can_tx_msg->tx_in)); + sgs[0] = sg_out; + sgs[1] = sg_in; + + putidx = virtio_can_alloc_tx_idx(priv); + + if (unlikely(putidx < 0)) { + netif_stop_queue(dev); + kfree(can_tx_msg); + netdev_warn(dev, "TX: Stop queue, no putidx available\n");If I understand things correctly, this code is on the datapath. So perhaps these should be rate limited, or only logged once. Likewise elsewhere in this function.
This block is almost a never. Like all blocks returning NETDEV_TX_BUSY. virtio_can_alloc_tx_idx() may return on error -ENOSPC or -ENOMEM.The queue is stopped under "/* Normal queue stop when no transmission slots are left */" before -ENOSPC is seen here. When -ENOMEM is returned we have more severe problems as some trace, considered as a theoretical issue only. So if the trace is seen most likely flow control got broken, needs to be fixed and I won't want to miss this.
Below is the "normal flow control" block which is likely to be entered under load. Everything else returning NETDEV_TX_BUSY is "never" or at least "almost never".+ xmit_ret = NETDEV_TX_BUSY; + goto kick; + } + + 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 (err != 0) { /* unlikely when vq->num_free was considered */ + 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); + if (err == -ENOSPC) + netdev_dbg(dev, "TX: Stop queue, no space left\n"); + else + netdev_warn(dev, "TX: Stop queue, reason = %d\n", err); + xmit_ret = NETDEV_TX_BUSY; + goto kick; + }
+ /* Normal queue stop when no transmission slots are left */ + if (atomic_read(&priv->tx_inflight) >= priv->can.echo_skb_max || + vq->num_free == 0 || (vq->num_free < 2 && + !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; +}...
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