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Date:	Thu, 20 Dec 2012 18:51:15 +0100
From:	Nicolas Ferre <>
To:	Erwin Rol <>
CC:	<>,
	Havard Skinnemoen <>,
	linux-arm-kernel <>,
	<>, netdev <>
Subject: Re: at91sam9260 MACB problem with IP fragmentation

On 12/20/2012 10:17 AM, Erwin Rol :
> 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.
> <snip>
>>> 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?

Any digging is interesting for me.

>> 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 ?

Yes, I see unexpected things happening but as I am connected to a whole
company network so maybe some broadcast packets are unlocking the
Anyway, I am continuing to investigate.

Best regards,--
Nicolas Ferre
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