netdev - Re: [PATCH 1/1] driver: net: smsc911x: set NOCARRIER flag in driver initialization

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Date:	Tue, 3 Jun 2014 09:29:24 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Balakumaran Kannan <kumaran.4353@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Steve Glendinning <steve.glendinning@...well.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/1] driver: net: smsc911x: set NOCARRIER flag in driver initialization

2014-06-03 7:15 GMT-07:00 Balakumaran Kannan <kumaran.4353@...il.com>:
> On Sat, May 31, 2014 at 2:12 AM, David Miller <davem@...emloft.net> wrote:
>> From: Balakumaran Kannan <kumaran.4353@...il.com>
>> Date: Fri, 30 May 2014 18:35:43 +0530
>>
>>> All these drivers call netif_carrier_off function after registering
>>> the network device using register_netdev.
>>
>> I can quote more counter-examples than your list, starting with the
>> Broadcom tg3 driver.
>
> Thank you David for this information. I'll send updated patch as version-2.
>
> Still I couldn't understand the reason behind this. I should be grateful if you
> would explain me little bit.

I believe one reason is that as soon as you call register_netdev(),
the network device notifiers run as part of call_netdevice_notifiers()
and it is valid for a notified callback to open your network device.
This means that you can call the driver's ndo_open() before you
returned from register_netdev(). If netif_carrier_off() is called
after register_netdev(), there is a risk for ndo_open() not to get a
consistent carrier state, and the actual call to netif_carrier_off()
to mess things up.
-- 
Florian
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