netdev - Re: [PATCH v4 0/5] net: Unified offload configuration

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Message-ID: <20110207224937.GA32549@rere.qmqm.pl>
Date:	Mon, 7 Feb 2011 23:49:37 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, bhutchings@...arflare.com
Subject: Re: [PATCH v4 0/5] net: Unified offload configuration

On Mon, Feb 07, 2011 at 01:37:21PM -0800, David Miller wrote:
> From: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> Date: Thu,  3 Feb 2011 15:21:21 +0100 (CET)
> > Here's a v4 of the ethtool unification patch series.
[cut list]
> After these changes the ethtool output is now inaccurate for
> RX checksumming.
> 
> Before:
> 
> davem@...amba:~$ /usr/sbin/ethtool -k eth0
> Offload parameters for eth0:
> rx-checksumming: on
> tx-checksumming: on
[...]
 
> After:
> 
> davem@...amba:~$ /usr/sbin/ethtool -k eth0
> Offload parameters for eth0:
> rx-checksumming: off
> tx-checksumming: on
[...]
> 
> If the issue is that you require driver or ethtool utility changes in
> order for things to keep working properly, then that is not
> acceptable.

> I'm reverting all of these changes, resubmit them when you have them
> in a state such that no regressions will be introduced.

What driver did you get this output from?  All drivers that implement
set_rx_csum also implement their own get_rx_csum and so should not be
affected by patch #4. For others that don't implement get_rx_csum
rx-checksumming status is unreliable. Looking at random drivers:
 - via-rhine: will advertise rx-checksumming when it doesn't support
	it (as a side effect of hardware workaround - checksum in driver)
 - sunhme: has no way to disable rx- and tx-checksumming so was
	correctly showing rx-checksumming enabled
 - 8139too: will show rx-checksumming enabled but doesn't support it
	(side effect of hardware workaround - checksumming in driver)

I wouldn't be suprised if there was a driver which doesn't advertise
RX checksumming but use it anyway.

So yes - this patchset uncovers bugs in drivers. I'll see how can I
make the RXCSUM patch retain the previous behaviour for this case.

Best Regards,
Michał Mirosław
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