netdev - Re: [PATCH net v4] smsc911x: only update stats when interface is up

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Date:   Fri, 31 Mar 2023 08:02:21 +0200
From:   Wolfram Sang <wsa+renesas@...g-engineering.com>
To:     Steen.Hegelund@...rochip.com
Cc:     netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        steve.glendinning@...well.net, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        geert+renesas@...der.be, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v4] smsc911x: only update stats when interface is up


> > +       if (pdata->is_open) {
> 
> Couldn't you just use netif_carrier_ok() here and drop the is_open
> variable?

From my research, I can't:

1) netif_carrier_ok() uses __LINK_STATE_NOCARRIER
2) __LINK_STATE_NOCARRIER gets cleared in netif_carrier_on()
3) netif_carrier_on() is this code:

	if (test_and_clear_bit(__LINK_STATE_NOCARRIER, &dev->state)) {
		if (dev->reg_state == NETREG_UNINITIALIZED)
			return;
		atomic_inc(&dev->carrier_up_count);
		linkwatch_fire_event(dev);
		if (netif_running(dev))
			__netdev_watchdog_up(dev);
	}

4) Notice the last if. It checks netif_running(). So, it is possible to
have the carrier on and the device not opened yet.
5) Sadly, no cigar. If I didn't miss something...

But thanks for the suggestion! Happy hacking,

   Wolfram


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