From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down) Date: Sat, 30 Jun 2007 14:10:58 -0400 Message-ID: <20070630141058.4c678c37@oldman> References: <4354d3270706300447ladcda4by987b1f87963112f9@mail.gmail.com> <20070630120541.GA21339@srcf.ucam.org> <46866C6B.9010801@linux.intel.com> <468687DE.6030003@garzik.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Arjan van de Ven , Matthew Garrett , =?UTF-8?B?VMO2csO2aw==?= Edvin , netdev@vger.kernel.org, power@bughost.org, zambrano@broadcom.com, linux-kernel@vger.kernel.org To: Jeff Garzik Return-path: Received: from smtp2.linux-foundation.org ([207.189.120.14]:43383 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752552AbXF3SLW (ORCPT ); Sat, 30 Jun 2007 14:11:22 -0400 In-Reply-To: <468687DE.6030003@garzik.org> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Sat, 30 Jun 2007 12:42:06 -0400 Jeff Garzik wrote: > Arjan van de Ven wrote: > > Matthew Garrett wrote: > >> Do you still get link beat detection when the phy is powered down? > > > does that matter? > > If the interface is down, nic drivers aren't expected to detect link... > > if userspace wants to find link status it should have the interface up. > > > Definitely matters. Switch renegotiation can take a while, and you must > take into account the common case of interface bouncing (immediate down, > then up). > > Hoards actively complained the few times we experimented with this, > because of e.g. DHCP's habit of bouncing the interface, which resulted > in PHY power bouncing, which resulted in negotiation, which resulted in > an excrutiating wait on various broken or stupid switches. > > Overall, this may be classed with other problems of a similar sort: we > can power down a PHY, but that removes hotplug capability and extends > partner/link negotiation time. > > Like SATA, we actually want to support BOTH -- active hotplug and PHY > power-down -- and so this wanders into power management policy. > > Give me a knob, and we can program plenty of ethernet|SATA|USB|... > drivers to power down the PHY and save power. > > Jeff We do have IFF_DORMANT, but almost no driver uses it. And most certainly, the common applications wouldn't know how to use it.