Messages in this thread | | | From | Hayes Wang <> | Subject | RE: [PATCH net-next] r8152: divide the tx and rx bottom functions | Date | Fri, 16 Aug 2019 09:08:41 +0000 |
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Eric Dumazet [mailto:eric.dumazet@gmail.com] > Sent: Friday, August 16, 2019 4:20 PM [...] > Which callback ?
The USB device has two endpoints for Tx and Rx. If I submit tx or rx URB to the USB host controller, the relative callback functions would be called, when they are finished. For rx, it is read_bulk_callback. For tx, it is write_bulk_callback.
> After an idle period (no activity, no prior packets being tx-completed ...), > a packet is sent by the upper stack, enters the ndo_start_xmit() of a network > driver. > > This driver ndo_start_xmit() simply adds an skb to a local list, and returns.
Base on the current method (without tasklet), when ndo_start_xmit() is called, napi_schedule is called only if there is at least one free buffer (!list_empty(&tp->tx_free)) to transmit the packet. Then, the flow would be as following.
- Call r8152_poll -- Call bottom_half --- Call tx_bottom ---- Call r8152_tx_agg_fill ----- submit tx urb
- Call write_bulk_callback if tx is completed
When the tx transfer is completed, write_bulk_callback would be called. And it would check if there is any tx packet in &tp->tx_queue and determine whether it is necessary to schedule the napi again or not.
> Where/how is scheduled this callback ?
For tx, you could find the following code in r8152_tx_agg_fill().
usb_fill_bulk_urb(agg->urb, tp->udev, usb_sndbulkpipe(tp->udev, 2), agg->head, (int)(tx_data - (u8 *)agg->head), (usb_complete_t)write_bulk_callback, agg); ret = usb_submit_urb(agg->urb, GFP_ATOMIC);
For rx you could find the following code in r8152_submit_rx().
usb_fill_bulk_urb(agg->urb, tp->udev, usb_rcvbulkpipe(tp->udev, 1), agg->buffer, tp->rx_buf_sz, (usb_complete_t)read_bulk_callback, agg);
ret = usb_submit_urb(agg->urb, mem_flags);
> Some kind of timer ? > An (unrelated) incoming packet ?
When the rx or tx is completed, a interrupt of USB host controller would be triggered. Then, the callback functions would be called.
Best Regards, Hayes
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