netdev - Re: [PATCHv3 2/2] tg3: Allow ethtool to enable/disable loopback.

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Message-ID: <1304525333.2926.2.camel@bwh-desktop>
Date:	Wed, 04 May 2011 17:08:53 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	Mahesh Bandewar <maheshb@...gle.com>,
	Matt Carlson <mcarlson@...adcom.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Michael Chan <mchan@...adcom.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCHv3 2/2] tg3: Allow ethtool to enable/disable loopback.

On Wed, 2011-05-04 at 18:05 +0200, Michał Mirosław wrote:
> On Wed, May 04, 2011 at 08:04:08AM -0700, Stephen Hemminger wrote:
> > On Wed, 4 May 2011 13:11:12 +0200
> > Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:
> > > On Tue, May 03, 2011 at 06:18:55PM -0700, Mahesh Bandewar wrote:
> > > > This patch adds tg3_set_features() to handle loopback mode. Currently the
> > > > capability is added for the devices which support internal MAC loopback mode.
> > > > So when enabled, it enables internal-MAC loopback.
> > > [...]
> > > > diff --git a/drivers/net/tg3.c b/drivers/net/tg3.c
> > > > index 7c7c9a8..46de633 100644
> > > > --- a/drivers/net/tg3.c
> > > > +++ b/drivers/net/tg3.c
> > > > @@ -6319,6 +6319,51 @@ static u32 tg3_fix_features(struct net_device *dev, u32 features)
> > > >  	return features;
> > > >  }
> > > >  
> > > > +static int tg3_set_features(struct net_device *dev, u32 features)
> > > > +{
> > > > +	struct tg3 *tp = netdev_priv(dev);
> > > > +	u32 cur_mode = 0;
> > > > +	int err = 0;
> > > > +
> > > > +	if (!netif_running(dev)) {
> > > > +		err = -EAGAIN;
> > > > +		goto sfeatures_out;
> > > > +	}
> > > netdev_update_features() is not designed to handle -EAGAIN from
> > > ndo_set_features callback. It might be useful to implement this
> > > handling, but in this case you should just return 0 and check
> > > dev->features in ndo_open callback.
> > 
> > EAGAIN is a bad choice of error code anyway. It implies that the
> > application should retry, which in this case is not true.
> > 
> > This error code is used for things like flow controlled sockets where
> > the application should do a select/poll and the condition will clear
> > when other side has read.
> > 
> > Why not use ENETDOWN instead?
> 
> The "application" here is netdev_update_features() here. Whatever the
> error code, it would need to be handled there.

The important point - which I think you already stated - is that when
the device is down this function is not expected to apply changes to the
hardware and therefore it should return 0.

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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