Re: [PATCH v7 4/7] can: Add Nuvoton NCT6694 CANFD support

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 08.02.2025 00:00:43, Vincent Mailhol wrote:
> On 07/02/2025 at 21:15, Marc Kleine-Budde wrote:
> > On 07.02.2025 15:44:59, Ming Yu wrote:
> 
> (...)
> 
> >> +static netdev_tx_t nct6694_can_start_xmit(struct sk_buff *skb,
> >> +					  struct net_device *ndev)
> >> +{
> >> +	struct nct6694_can_priv *priv = netdev_priv(ndev);
> >> +
> >> +	if (can_dev_dropped_skb(ndev, skb))
> >> +		return NETDEV_TX_OK;
> >> +
> >> +	netif_stop_queue(ndev);
> >> +	can_put_echo_skb(skb, ndev, 0, 0);
> >> +	queue_work(priv->wq, &priv->tx_work);
> 
> What is the reason to use a work queue here? xmit() is not a hard IRQ.
> Also, the other USB CAN devices just directly send the USB message in
> their xmit() without the need to rely on such worker.
> 
> Sorry if this was discussed in the past, I can not remember if this
> question has already been raised.

AFAICS xmit uses nct6694_write_msg(), which uses several usb_bulk_msg(),
that can only be used from task context.

You can build a chain of usb_fill_bulk_urb(), usb_submit_urb(),
callbacks instead, but that's hard to read compared to blocking
usb_bulk_msg()s.

Marc

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