netdev - Re: Gianfar : Q : Tx VLAN hardware accelaration

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Date:	Mon, 4 Feb 2013 12:04:07 +0200
From:	Claudiu Manoil <claudiu.manoil@...escale.com>
To:	voncken <cedric.voncken@...sys.fr>
CC:	<netdev@...r.kernel.org>
Subject: Re: Gianfar : Q : Tx VLAN hardware accelaration

On 2/1/2013 11:45 AM, voncken wrote:
> 	Hi Claudiu,
>
> I would like to send on the same Ethernet interface (so the same eTSEC) a
> frame with VLAN tag and without VLAN tag.
>
> If I understand correctly mpc8315 Family reference manual rev 2, when TX
> VLAN hardware acceleration is enable, the eTSEC always add the VLAN TAG
> -from FCB or from the default TAG register).
>
> Could you confirm is not possible to send frame without tag when Tx VLAN
> hardware acceleration is enable?
>
> Thanks
>

Hi Cedric,
If I remember correctly, if the hw vlan tag insertion feature is
activated then vlan tag 0 is inserted for non-vlan frames. VLAN-aware
hosts can deal with this, however this may pose problems for the
vlan-unaware ones (e.g. 802.1Q support not activated). I think this
is the main reason why the tx vlan accel is turned off by default.

regards,
Claudiu


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