netdev - Re: how PHY driver is notified that cable is unplugged? (possibly related to IFF

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Date:   Wed, 1 Aug 2018 17:45:31 -0400 (EDT)
From:   "Robert P. J. Day" <rpjday@...shcourse.ca>
To:     Florian Fainelli <f.fainelli@...il.com>
cc:     netdev@...r.kernel.org, andrew@...n.ch
Subject: Re: how PHY driver is notified that cable is unplugged? (possibly
 related to IFF_RUNNING flag)

On Wed, 1 Aug 2018, Florian Fainelli wrote:

> On 08/01/2018 05:58 AM, rpjday@...shcourse.ca wrote:
> >
> >   (warning that i have a few questions that are probably trivial
> > until i get up to speed with networking code.)
> >
> >   a colleague asked for advice about the following -- apparently a
> > new PHY driver works properly when being brought up with "ifconfig
> > <ifname> up", part of that process apparently setting the
> > IFF_RUNNING net_device flags bit. so far, so good.
> >
> >   now, when the cable is physically unplugged, the claim is that
> > there is no obvious status change for that port, accompanied by
> > the suggestion that it is that IFF_RUNNING flag bit that is not
> > being unset.
> >
> >   asking a more general question, where can i read up on the
> > proper protocol for a driver being notified of, and properly
> > handling, physical disconnection on that port? and, of course, the
> > cable being plugged back in.
>
> The basic mechanism used by the PHY library is to read the standard
> Basic Mode Status Register and check the Link status bit to
> determine what the state of the link is set. This event can be
> triggered either through polling, or the use of an interrupt that
> the PHY is generating.
>
> Once the link state is determined, because the PHY device is
> "connected" to a network device, the PHY library can call
> netif_carrier_{on,off} against the network device attached to the
> PHY and that propagates through the networking stack and sets the
> appropriate bits, including IFF_RUNNING.

  yup, that agrees with the code i was perusing, thanks for
clarifying. more questions coming shortly, hopefully tougher.

rday