netdev - Re: [PATCH 1/1] net: Set NOCARRIER bit of etherdev state at initialization

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Date:	Tue, 27 May 2014 10:24:20 -0500
From:	Dan Williams <dcbw@...hat.com>
To:	Balakumaran Kannan <kumaran.4353@...il.com>
Cc:	David Miller <davem@...emloft.net>, stephen@...workplumber.org,
	Avinash Kumar <avi.kp.137@...il.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] net: Set NOCARRIER bit of etherdev state at
 initialization

On Sat, 2014-05-24 at 18:52 +0530, Balakumaran Kannan wrote:
> On Fri, May 23, 2014 at 11:45 PM, David Miller <davem@...emloft.net> wrote:
> > From: Dan Williams <dcbw@...hat.com>
> > Date: Fri, 23 May 2014 12:38:01 -0500
> >
> >> The current "carrier on until told otherwise" model is intentional,
> >> because not all drivers support carrier detection, and thus we must
> >> assume the carrier is on until the driver tells us it is not on.
> >>
> >> Would this patch break that model?
> >
> > Absolutely correct, this change is completely inappropriate.
> 
> So it is driver's responsibility to maintain this flag appropriately.
> Thus if a driver supports carrier detection, it should set "carrier
> on" only after determining the carrier state. Then I'll add
> 'netif_carrier_off' call to smsc911x driver and send a new patch.

Correct.  Carrier state starts with ON.  If the driver knows it can
detect carrier state, then the driver should call netif_carrier_off()
early in the driver initialization, and then call on/off as appropriate
when it gets carrier change events.

Dan

> Thanks for the explanation.
> 
> Regards,
> K.Balakumaran
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