From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: RFC - document network device carrier management Date: Mon, 20 Aug 2012 22:34:25 +0100 Message-ID: <1345498465.2659.41.camel@bwh-desktop.uk.solarflarecom.com> References: <20120815085827.2b252094@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: David Miller , To: Stephen Hemminger Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:54437 "EHLO ocex02.SolarFlarecom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751836Ab2HTVe2 (ORCPT ); Mon, 20 Aug 2012 17:34:28 -0400 In-Reply-To: <20120815085827.2b252094@nehalam.linuxnetplumber.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2012-08-15 at 08:58 -0700, Stephen Hemminger wrote: > Since carrier handling is often done incorrectly by new device drivers > be explicit about carrier handling API. > > Signed-off-by: Stephen Hemminger > > --- > This is a meant as starting point for discussion, it's probably wrong as is. > Since this isn't code, it could be applied for 3.6 and doesn't need for net-next. > > > --- a/Documentation/networking/netdevices.txt 2012-06-22 08:27:46.729168196 -0700 > +++ b/Documentation/networking/netdevices.txt 2012-08-15 08:56:31.120429994 -0700 > @@ -45,6 +45,36 @@ drop, truncate, or pass up oversize pack > packets is preferred. > > > +CARRIER > +======= > +Most network devices have an operational state that the device > +monitors. The Linux kernel uses the name "carrier" for this flag which > +is a historical reference to old modems. Carrier is reported to > +userspace via the IFF_RUNNING flag from SIOCGIFFLAGS ioctl. > +Carrier is controlled in the device driver > +by the functions netif_carrier_on and netif_carrier_off. These > +functions trigger the necessary netlink and userspace API changes; > +device drivers must not change netdevice->flags directly. > + > +The carrier defaults to ON when the device is created and registered. > +Simple devices (such as dummy) do not need to do anything. > +Ethernet style devices should: > + * alloc_etherdev in probe routine > + * call netif_carrier_off > + * register network device > + * start auto negotiation with phy in open routine Auto-negotiation is only one of several stages of link setup, and of course is not used in all Ethernet physical layers. I think the important point is that once the ndo_open method returns the hardware and driver should be ready to set up the link and report this state whenever a suitable partner is physically connected. > + * call netif_carrier_on when link is up > + > +More complex RFC2863 style operational state is also possible > +but not required (see operstates.txt). Drivers are not allowed to set operstate directly. > +The monitoring of link state is the responsibility of the network > +device driver. It can be done by polling, interrupt, or any other > +mechanism. netif_carrier_on/netif_carrier_off are atomic and can > +safely be called by an interrupt routine. Carrier events are > +managed by the linkwatch work queue and limited to one per second > +to avoid overwhelming management applications. > + > struct net_device synchronization rules > ======================================= > ndo_open: -- Ben Hutchings, Staff 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.