netdev - Re: [PATCH 4/4] Ethtool: convert get_tx_csum/set_tx_csum calls to hw

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Date:	Tue, 2 Nov 2010 02:23:45 +0100
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	Steve Glendinning <steve.glendinning@...c.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Rasesh Mody <rmody@...cade.com>,
	Debashis Dutt <ddutt@...cade.com>,
	Kristoffer Glembo <kristoffer@...sler.com>,
	linux-driver@...gic.com, linux-net-drivers@...arflare.com
Subject: Re: [PATCH 4/4] Ethtool: convert get_tx_csum/set_tx_csum calls to
	hw_features flags

On Mon, Nov 01, 2010 at 09:38:57PM +0000, Ben Hutchings wrote:
> On Sun, 2010-10-31 at 02:09 +0200, Michał Mirosław wrote:
> [...]
> > diff --git a/drivers/net/dm9000.c b/drivers/net/dm9000.c
> > index 9f6aeef..5ba4535 100644
> > --- a/drivers/net/dm9000.c
> > +++ b/drivers/net/dm9000.c
> > @@ -132,7 +132,6 @@ typedef struct board_info {
> >  	u32		wake_state;
> >  
> >  	int		rx_csum;
> > -	int		can_csum;
> >  	int		ip_summed;
> >  } board_info_t;
> >  
> > @@ -480,7 +479,7 @@ static int dm9000_set_rx_csum_unlocked(struct net_device *dev, uint32_t data)
> >  {
> >  	board_info_t *dm = to_dm9000_board(dev);
> >  
> > -	if (dm->can_csum) {
> > +	if (dev->hw_features & NETIF_F_IP_CSUM) {
> 
> This is a bit ugly because can_csum is being used to indicate RX
> checksum offload capability whereas the checksum feature flags logically
> indicate TX checksum offload capability.  Of course, the two hardware
> features are highly correlated!

I briefly looked over the code. can_csum looked like "can do both TX
and RX checksum", so (dev->hw_features & NETIF_F_IP_CSUM) duplicates
information in this case. I can remove this change or just add a comment
that we abuse hw_features a bit.

> [...]
> > diff --git a/net/core/ethtool.c b/net/core/ethtool.c
> > index 9b0e598..95e8b7a 100644
> > --- a/net/core/ethtool.c
> > +++ b/net/core/ethtool.c
> [...]
> > @@ -1077,12 +1039,18 @@ static int __ethtool_set_sg(struct net_device *dev, u32 data)
> >  	return 0;
> >  }
> >  
> > +static u32 ethtool_get_tx_csum(struct net_device *dev)
> > +{
> > +	return (dev->features & (NETIF_F_ALL_CSUM|NETIF_F_SCTP_CSUM)) != 0;
> > +}
> > +
> [...]
> 
> It seems to me that NETIF_F_SCTP_CSUM should be added to
> NETIF_F_ALL_CSUM, though that may cause problems in some other places
> NETIF_F_ALL_CSUM is used.

This would need auditing NETIF_F_ALL_CSUM usage across the kernel, so
definitely a further patch material.

Best Regards,
Michał Mirosław
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