netdev - Re: [PATCH v5] net: bnx2x: convert to hw

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Date:	Thu, 21 Apr 2011 20:19:19 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Vladislav Zolotarov <vladz@...adcom.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Eilon Greenstein <eilong@...adcom.com>
Subject: Re: [PATCH v5] net: bnx2x: convert to hw_features

On Thu, 2011-04-21 at 21:49 +0300, Vladislav Zolotarov wrote:
[...]
> More than that, in addition it is impossible to disable the LRO with 
> the current bnx2x upstream driver (ethtool -K ethX lro off) and this is
> because dev_disable_lro passes to __ethtool_set_flags() flags based on
> the current value of dev->features while __ethtool_set_flags() expects
> only the flags set in dev->hw_features. bnx2x has NETIF_F_HW_VLAN_RX
> that is set in dev->features and not set in dev->hw_features and it's
> passed down to the __ethtool_set_flags(). 
[...]

The problem is here in register_netdevice():

	/* Transfer changeable features to wanted_features and enable
	 * software offloads (GSO and GRO).
	 */
	dev->hw_features |= NETIF_F_SOFT_FEATURES;
	dev->features |= NETIF_F_SOFT_FEATURES;
	dev->wanted_features = dev->features & dev->hw_features;

This doesn't work correctly for features that are always enabled, like
NETIF_F_HW_VLAN_RX in bnx2x, which are set in dev->features but not in
dev->hw_features.

The name 'hw_features' really wasn't a good choice - the obvious meaning
and the meaning assumed by this code is 'hardware-supported features'
and not 'hardware-supported features that can be toggled'.  And since we
add NETIF_F_SOFT_FEATURES, it really only means 'features that can be
toggled'.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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