Virtual device hdlc0 asks to que packet!

Joakim Tjernlund joakim.tjernlund at
Wed Mar 5 19:11:56 EST 2008

On Tue, 2008-03-04 at 15:33 -0800, Russell McGuire wrote:
> All,
> Background MPC8360, using a T1 PHY as an HDLC device.
> Developing my hdlc driver, and was writing a simple send utility. To test it
> out. Things seem well when I had massive delays in between the write() or
> sendot(), and I was able to attain 100+Kbytes/sec. However, when I replaced
> the simple usleeps(xxx) with select statements, suddenly I started getting a
> ton of these messages.
> "Virtual device hdlc0 asks to que packet!"
> Along with dropped or non-sent data.
> In my driver I am tracking the available TX buffers, and issue a
> netif_stop_que() statement inside the start_xmit() call, with a
> corresponding netif_wake_que() in the tx_handler.
> Is there something else that needs to be done in order to make a select
> statement wait for the socket to not be busy? It seems that it always
> returns immediately with no timeout.
> I guess the other pieces of the scenario are as follows:
> * Using 'sethdlc hdlc0 hdlc' for the mode, so no IP stack is used.
> * Opening the socket to the hdlc device directly to the device itself, i.e.
> no port number socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
> I have used both sendto() and write() to pass data down, and they both
> return as if all the data has been sent, i.e. I never get an error.
> -Russ

When playing with your driver I noticed that the hdlc interfaces had
Normal eth interfaces has txqueuelen:1000. Maybe you need to add a
txqueue to the hdlc interfaces?


    The driver seems to work now, I get both TX and RX IRQs now.

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