Re: [Qemu-devel] Segfault using qemu-system-arm in smc91c111

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Sun, 2015-09-06 at 17:48 -0700, Peter Crosthwaite wrote:
> This doesn't sound right. There are other network controllers that
> rely of can_receive catching all cases properly. Is this a regression?
> Looking at logs, I see some refactoring of QEMU net framework around
> June timeframe, if you rewind to QEMU 2.3 (or earlier) does the bug go
> away?

I did find an interesting comment in this commit:

http://git.qemu.org/?p=qemu.git;a=commitdiff;h=625de449fc5597f2e1aff9cb586e249e198f03c9

"""
Since commit 6e99c63 "net/socket: Drop net_socket_can_send" and friends,
net queues need to be explicitly flushed after qemu_can_send_packet()
returns false, because the netdev side will disable the polling of fd.
"""

smc91x111 is calling flush functions when it knows can_receive
would/should return false. I believe that is the bug here.

I suspect the driver needs:

* can_receive to actually return the right value
* the locations of the flush calls to be when there is receive space 

This could explain what changed to break this and why moving the flush
calls works in my patch.

Cheers,

Richard