Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759679AbXF3QmY (ORCPT ); Sat, 30 Jun 2007 12:42:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757710AbXF3QmO (ORCPT ); Sat, 30 Jun 2007 12:42:14 -0400 Received: from srv5.dvmed.net ([207.36.208.214]:37020 "EHLO mail.dvmed.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756267AbXF3QmN (ORCPT ); Sat, 30 Jun 2007 12:42:13 -0400 Message-ID: <468687DE.6030003@garzik.org> Date: Sat, 30 Jun 2007 12:42:06 -0400 From: Jeff Garzik User-Agent: Thunderbird 1.5.0.12 (X11/20070530) MIME-Version: 1.0 To: Arjan van de Ven CC: Matthew Garrett , =?ISO-8859-1?Q?T=F6r=F6k_Edv?= =?ISO-8859-1?Q?in?= , netdev@vger.kernel.org, power@bughost.org, zambrano@broadcom.com, linux-kernel@vger.kernel.org Subject: PM policy, hotplug, power saving (was Re: [PATCH] b44: power down PHY when interface down) References: <4354d3270706300447ladcda4by987b1f87963112f9@mail.gmail.com> <20070630120541.GA21339@srcf.ucam.org> <46866C6B.9010801@linux.intel.com> In-Reply-To: <46866C6B.9010801@linux.intel.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -4.3 (----) X-Spam-Report: SpamAssassin version 3.1.9 on srv5.dvmed.net summary: Content analysis details: (-4.3 points, 5.0 required) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 36 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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/