netdev - RE: [net-next-2.6 PATCH 6/9] vxge: Check if FCS stripping is disabled by the firmware.

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Message-ID: <78C9135A3D2ECE4B8162EBDCE82CAD7705C16350@nekter>
Date:	Tue, 6 Oct 2009 02:41:26 -0400
From:	"Ramkrishna Vepa" <Ramkrishna.Vepa@...erion.com>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"Sreenivasa Honnur" <Sreenivasa.Honnur@...erion.com>
Cc:	<davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: RE: [net-next-2.6 PATCH 6/9] vxge: Check if FCS stripping is disabled by the firmware.

> > - Added a function to check if FCS stripping is disabled by the
> firmware, if
> >   it is not disabled fail driver load.
> >
> > - By default FCS stripping is disabled by the firmware. With this
> assumption
> >   driver decrements the indicated packet length by 4 bytes(FCS
length).
> >
> > - This patch ensures that FCS stripping is disabled during driver
load
> time.
> >
> > Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@...erion.com>
> 
> What the big deal about FCS not being stripped ?
[Ram] The minimum frame size that can be received by the hardware is 57
Bytes. A 64 Byte Ethernet frame with the vlan tag and fcs stripped will
result in a 56 Byte frame which will lock up the receive engine. The
work around is to disable fcs stripping in the hardware which is a
privileged operation done with a firmware version that the driver checks
for currently.

Ram
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