netdev - Re: [PATCH 3/3] net: Fix drivers advertising HW_CSUM feature to use csum

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Date:	Wed, 15 Dec 2010 10:25:36 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	Vasanthy Kolluri <vkolluri@...co.com>,
	Roopa Prabhu <roprabhu@...co.com>,
	David Wang <dwang2@...co.com>,
	Andrew Gallatin <gallatin@...i.com>,
	Brice Goglin <brice@...i.com>,
	Shreyas Bhatewara <sbhatewara@...are.com>,
	"VMware, Inc." <pv-drivers@...are.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Jiri Pirko <jpirko@...hat.com>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	Jie Yang <Jie.Yang@...eros.com>, Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 3/3] net: Fix drivers advertising HW_CSUM feature to use
 csum_start

On Wed, 15 Dec 2010 19:16:55 +0100
Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:

> On Tue, Dec 14, 2010 at 07:07:27PM -0800, Stephen Hemminger wrote:
> > On Wed, 15 Dec 2010 02:24:08 +0100 (CET)
> > Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:
> > > Some drivers are using skb_transport_offset(skb) instead of skb->csum_start
> > > for NETIF_F_HW_CSUM offload.  This does not matter now, but if someone
> > > implements checksumming of encapsulated packets then this will break silently.
> > > 
> > > TSO output paths are left as they are, since they are for IP+TCP only
> > > (might be worth converting though).
> > > 
> > > Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > Which if any of these drivers did you test on real hardware?
> 
> I'm running it on skge, with additional patch that changes it to use
> NETIF_F_HW_CSUM instead of NETIF_F_IP_CSUM. BTW, why it is not advertising
> full HW checksum in vanilla kernel? Are there any known hardware bugs in there?
> 
> Best Regards,
> Michał Mirosław

The driver was written from vendor sk98lin driver and that driver
only did IP checksum, therefore I did not trust the hardware.
The chipset is old, and not used in new designs, no documentation
is up to date (and I didn't have any).

Please don't enable non-IPv4 checksum offload on this hardware, there
is too big a risk of it not working on all hardware.

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