netdev - Re: [PATCH 5/7] sfc: Work around XMAC bug causing packet loss with some peers

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Message-Id: <20090826.180420.114585490.davem@davemloft.net>
Date:	Wed, 26 Aug 2009 18:04:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	netdev@...r.kernel.org, linux-net-drivers@...arflare.com
Subject: Re: [PATCH 5/7] sfc: Work around XMAC bug causing packet loss with
 some peers

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Wed, 26 Aug 2009 19:17:59 +0100

> Received frames must be re-clocked by the local XGXS to the 156.25 MHz
> (DDR) clock of the XGMII.  If the remote clock is slightly faster this
> can reduce a minimum IPG of 64 bit-times (1 cycle) to 32 bit-times
> (half a cycle).  If the XMAC detects that a frame has reached the
> maximum RX frame length in the same cycle that it receives one of
> these reduced IPGs, it may miss the IPG, causing two valid frames to
> be treated as a single invalid frame (over-length with bad CRC).
> 
> We work around this by increasing the maximum RX frame length so that
> peers with matched MTU will not provoke this bug.
> 
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>

Applied.
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