From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755954AbXGAEvs (ORCPT ); Sun, 1 Jul 2007 00:51:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751321AbXGAEvl (ORCPT ); Sun, 1 Jul 2007 00:51:41 -0400 Received: from smtpout.mac.com ([17.250.248.174]:64941 "EHLO smtpout.mac.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751125AbXGAEvk (ORCPT ); Sun, 1 Jul 2007 00:51:40 -0400 In-Reply-To: <468687DE.6030003@garzik.org> References: <4354d3270706300447ladcda4by987b1f87963112f9@mail.gmail.com> <20070630120541.GA21339@srcf.ucam.org> <46866C6B.9010801@linux.intel.com> <468687DE.6030003@garzik.org> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <05EEFFFE-AD93-40A1-8851-92C3053286E1@mac.com> Cc: Arjan van de Ven , Matthew Garrett , =?ISO-8859-1?Q?T=F6r=F6k_Edvin?= , netdev@vger.kernel.org, power@bughost.org, zambrano@broadcom.com, linux-kernel@vger.kernel.org Content-Transfer-Encoding: 7bit From: Kyle Moffett Subject: Re: PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down) Date: Sun, 1 Jul 2007 00:51:15 -0400 To: Jeff Garzik X-Mailer: Apple Mail (2.752.2) X-Brightmail-Tracker: AAAAAA== X-Brightmail-scanned: yes Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Jun 30, 2007, at 12:42:06, Jeff Garzik wrote: > 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. With some buggy switches and other hardware you actually *want* to bounce the link to get them to properly renegotiate. I can also see wanting to power off and on a single-PoE-port NIC to restart whatever device is at the other end, although I don't know if any such devices exist. Currently the tg3 driver turns the PHY off and on during down/ up on a few of my systems, which I use to make a buggy no-name switch recognize STP changes properly. Cheers, Kyle Moffett