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Date:	Thu, 20 Dec 2012 10:17:49 +0100
From:	Erwin Rol <>
To:	Nicolas Ferre <>
	Havard Skinnemoen <>,
	linux-arm-kernel <>,, netdev <>
Subject: Re: at91sam9260 MACB problem with IP fragmentation

Hallo Nicolas,

On 6-12-2012 14:27, Nicolas Ferre wrote:
> Erwin,
> On 12/06/2012 12:32 PM, Erwin Rol :
>> Hello Nicolas, Havard, all,
>> I have a very obscure problem with a at91sam9260 board (almost 1 to 1
>> copy of the Atmel EK).
>> The MACB seems to stall when I use large (>2 * MTU) UDP datagrams. The
>> test case is that a udp echo client (PC) sends datagrams with increasing
>> length to the AT91 until the max length of the UDP datagram is reached.
>> When there is no IP fragmentation everything is fine, but when the
>> datagrams are starting to get fragmented the AT91 will not reply
>> anymore. But as soon as some network traffic happens it goes on again,
>> and non of the data is lost.


>> I tried several kernels including the test version from Nicolas that he
>> posted on LKML in October. They all show the same effect.
> [..]
> It seems that Matteo has the same behavior: check here:

I tried Matteo's patch and it seems to work. But I don't know if the
patch is really the right solution. I checked again with wireshark and
it really seems the sending that stalls not the receiving. But as soon
as a ethernet frame is received the sending "un-stalls". So maybe the
patch just causes an MACB IRQ at certain moments that causes the sending
to continue?

> I am working on the macb driver right now, so I will try to reproduce
> and track this issue on my side.

Any luck reproducing it ?

- Erwin

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