netdev - Re: [PATCH] net offloading: Do not mask out NETIF_F_HW_VLAN

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Date:	Tue, 18 Jan 2011 09:21:52 -0800
From:	"Michael Chan" <mchan@...adcom.com>
To:	"Jesse Gross" <jesse@...ira.com>
cc:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"David Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH] net offloading: Do not mask out NETIF_F_HW_VLAN_TX
 for vlan.


On Mon, 2011-01-17 at 23:12 -0800, Jesse Gross wrote:
> On Tue, Jan 18, 2011 at 1:55 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > Le lundi 17 janvier 2011 à 22:46 -0800, Jesse Gross a écrit :
> >> In netif_skb_features() we return only the features that are valid for vlans
> >> if we have a vlan packet.  However, we should not mask out NETIF_F_HW_VLAN_TX
> >> since it enables transmission of vlan tags and is obviously valid.
> >>
> >> Reported-by: Eric Dumazet <eric.dumazet@...il.com>
> >> Signed-off-by: Jesse Gross <jesse@...ira.com>
> >
> > Thanks Jesse
> >
> > Acked-by: Eric Dumazet <eric.dumazet@...il.com>
> >
> > Now back to the "ethtool -K eth0 txvlan off" problem on bnx2
> >
> > Is it a driver/software problem or hardware/firmware one ?
> 
> CC'ing Michael Chan
> 
> It looks like bnx2 is storing the offsets of various headers so the
> hardware can find them for TSO.  The parsing logic doesn't do anything
> for vlan tags, so the hardware gets confused if one is present in the
> packet itself.

Yeah, I don't think the hardware/firmware can replicate the vlan tag +
headers properly for TSO if there is a VLAN tag in the packet.  Even
simple tx checksum offload may have problem, but I'll need to check.

> 
> Quick fix is to simply disallow disabling TX vlan offload or disable
> TSO at the same time or some other Ethtool game.  However, if the
> hardware supports it then it would be nicer to fix up the TSO setup
> logic.  Maybe we can just add the size of the vlan tag to the offset
> but I am not certain.  Michael, do you know if this is possible?
> 

I doubt it, as the VLAN tag needs to be replicated for each transmitted
packet.  I'll check with the firmware/hardware guys.

Thanks.


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