Re: [PATCH v2] can: kvaser_usb: Add support for Kvaser CAN/USB devices

Hi Oliver,

On Mon, Aug 06, 2012 at 10:10:43AM +0200, Oliver Neukum wrote:

On Monday 06 August 2012 07:21:29 Olivier Sobrie wrote:

quoted

This driver provides support for several Kvaser CAN/USB devices.
Such kind of devices supports up to three can network interfaces.

It has been tested with a Kvaser USB Leaf Light (one network interface)
connected to a pch_can interface.
The firmware version of the Kvaser device was 2.5.205.

quoted

+static netdev_tx_t kvaser_usb_start_xmit(struct sk_buff *skb,
+					 struct net_device *netdev)
+{
+	struct kvaser_usb_net_priv *priv = netdev_priv(netdev);
+	struct kvaser_usb *dev = priv->dev;
+	struct net_device_stats *stats = &netdev->stats;
+	struct can_frame *cf = (struct can_frame *)skb->data;
+	struct kvaser_usb_tx_urb_context *context = NULL;
+	struct urb *urb;
+	void *buf;
+	struct kvaser_msg *msg;
+	int i, err;
+	int ret = NETDEV_TX_OK;
+
+	if (can_dropped_invalid_skb(netdev, skb))
+		return NETDEV_TX_OK;
+
+	urb = usb_alloc_urb(0, GFP_ATOMIC);
+	if (!urb) {
+		netdev_err(netdev, "No memory left for URBs\n");
+		stats->tx_dropped++;
+		dev_kfree_skb(skb);
+		return NETDEV_TX_OK;
+	}
+
+	buf = usb_alloc_coherent(dev->udev, sizeof(struct kvaser_msg),
+				 GFP_ATOMIC, &urb->transfer_dma);

usb_alloc_coherent() as a rule only makes sense if you reuse the buffer
and in some cases not even then. Please use a simple kmalloc()

Ok thanks. I'll change it.

quoted

+	if (!buf) {
+		netdev_err(netdev, "No memory left for USB buffer\n");
+		stats->tx_dropped++;
+		dev_kfree_skb(skb);
+		goto nobufmem;
+	}
+
+	msg = (struct kvaser_msg *)buf;
+	msg->len = MSG_HEADER_LEN + sizeof(struct kvaser_msg_tx_can);
+	msg->u.tx_can.flags = 0;
+	msg->u.tx_can.channel = priv->channel;
+
+	if (cf->can_id & CAN_EFF_FLAG) {
+		msg->id = CMD_TX_EXT_MESSAGE;
+		msg->u.tx_can.msg[0] = (cf->can_id >> 24) & 0x1f;
+		msg->u.tx_can.msg[1] = (cf->can_id >> 18) & 0x3f;
+		msg->u.tx_can.msg[2] = (cf->can_id >> 14) & 0x0f;
+		msg->u.tx_can.msg[3] = (cf->can_id >> 6) & 0xff;
+		msg->u.tx_can.msg[4] = cf->can_id & 0x3f;
+	} else {
+		msg->id = CMD_TX_STD_MESSAGE;
+		msg->u.tx_can.msg[0] = (cf->can_id >> 6) & 0x1f;
+		msg->u.tx_can.msg[1] = cf->can_id & 0x3f;
+	}
+
+	msg->u.tx_can.msg[5] = cf->can_dlc;
+	memcpy(&msg->u.tx_can.msg[6], cf->data, cf->can_dlc);
+
+	if (cf->can_id & CAN_RTR_FLAG)
+		msg->u.tx_can.flags |= MSG_FLAG_REMOTE_FRAME;
+
+	for (i = 0; i < ARRAY_SIZE(priv->tx_contexts); i++) {
+		if (priv->tx_contexts[i].echo_index == MAX_TX_URBS) {
+			context = &priv->tx_contexts[i];
+			break;
+		}
+	}
+
+	if (!context) {
+		netdev_warn(netdev, "cannot find free context\n");
+		ret =  NETDEV_TX_BUSY;
+		goto releasebuf;
+	}
+
+	context->priv = priv;
+	context->echo_index = i;
+	context->dlc = cf->can_dlc;
+
+	msg->u.tx_can.tid = context->echo_index;
+
+	usb_fill_bulk_urb(urb, dev->udev,
+			  usb_sndbulkpipe(dev->udev,
+					  dev->bulk_out->bEndpointAddress),
+			  buf, msg->len,
+			  kvaser_usb_write_bulk_callback, context);
+	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+	usb_anchor_urb(urb, &priv->tx_submitted);
+
+	can_put_echo_skb(skb, netdev, context->echo_index);
+
+	atomic_inc(&priv->active_tx_urbs);
+
+	if (atomic_read(&priv->active_tx_urbs) >= MAX_TX_URBS)
+		netif_stop_queue(netdev);
+
+	err = usb_submit_urb(urb, GFP_ATOMIC);
+	if (unlikely(err)) {
+		can_free_echo_skb(netdev, context->echo_index);
+
+		atomic_dec(&priv->active_tx_urbs);
+		usb_unanchor_urb(urb);
+
+		stats->tx_dropped++;
+
+		if (err == -ENODEV)
+			netif_device_detach(netdev);
+		else
+			netdev_warn(netdev, "Failed tx_urb %d\n", err);
+
+		goto releasebuf;
+	}
+
+	netdev->trans_start = jiffies;
+
+	usb_free_urb(urb);
+
+	return NETDEV_TX_OK;
+
+releasebuf:
+	usb_free_coherent(dev->udev, sizeof(struct kvaser_msg),
+			  buf, urb->transfer_dma);
+nobufmem:
+	usb_free_urb(urb);
+	return ret;
+}

quoted

+static int kvaser_usb_init_one(struct usb_interface *intf,
+			       const struct usb_device_id *id, int channel)
+{
+	struct kvaser_usb *dev = usb_get_intfdata(intf);
+	struct net_device *netdev;
+	struct kvaser_usb_net_priv *priv;
+	int i, err;
+
+	netdev = alloc_candev(sizeof(*priv), MAX_TX_URBS);
+	if (!netdev) {
+		dev_err(&intf->dev, "Cannot alloc candev\n");
+		return -ENOMEM;
+	}
+
+	priv = netdev_priv(netdev);
+
+	init_completion(&priv->start_comp);
+	init_completion(&priv->stop_comp);
+
+	init_usb_anchor(&priv->tx_submitted);
+	atomic_set(&priv->active_tx_urbs, 0);
+
+	for (i = 0; i < ARRAY_SIZE(priv->tx_contexts); i++)
+		priv->tx_contexts[i].echo_index = MAX_TX_URBS;
+
+	priv->dev = dev;
+	priv->netdev = netdev;
+	priv->channel = channel;
+
+	priv->can.state = CAN_STATE_STOPPED;
+	priv->can.clock.freq = CAN_USB_CLOCK;
+	priv->can.bittiming_const = &kvaser_usb_bittiming_const;
+	priv->can.do_set_bittiming = kvaser_usb_set_bittiming;
+	priv->can.do_set_mode = kvaser_usb_set_mode;
+	priv->can.ctrlmode_supported = CAN_CTRLMODE_3_SAMPLES;
+	if (id->driver_info & KVASER_HAS_SILENT_MODE)
+		priv->can.ctrlmode_supported |= CAN_CTRLMODE_LISTENONLY;
+
+	netdev->flags |= IFF_ECHO;
+
+	netdev->netdev_ops = &kvaser_usb_netdev_ops;
+
+	SET_NETDEV_DEV(netdev, &intf->dev);
+
+	err = register_candev(netdev);
+	if (err) {
+		dev_err(&intf->dev, "Failed to register can device\n");
+		free_candev(netdev);
+		return err;
+	}
+

Here the device is usable.

quoted

+	dev->nets[channel] = priv;

And only know you init this field. Looks like a race condition.

Argh... Indeed.
Thanks

quoted

+	netdev_dbg(netdev, "device registered\n");
+
+	return 0;
+}
+

quoted

+static void kvaser_usb_disconnect(struct usb_interface *intf)
+{
+	struct kvaser_usb *dev = usb_get_intfdata(intf);
+	int i;
+
+	usb_set_intfdata(intf, NULL);
+
+	if (!dev)
+		return;
+
+	for (i = 0; i < dev->nchannels; i++) {
+		if (!dev->nets[i])
+			continue;
+
+		unregister_netdev(dev->nets[i]->netdev);
+		free_candev(dev->nets[i]->netdev);
+	}
+
+	kvaser_usb_unlink_all_urbs(dev);

So what happens if an URB completes between freeing the candev
and unlinking and proceeds to push data to upper layers?

In this case I should avoid using netdev context, i.e. pointer to "struct
kvaser_usb_net_priv" in urb callbacks.
Is that what you mean?
I see it is well done in kvaser_usb_read_bulk_callback()
but not in kvaser_usb_write_bulk_callback().
I'll better protect the callbacks and move the free_candev after the
unlink.

Thank you,

-- 
Olivier