From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Garrett Subject: Re: [linux-pm] [RFC] Runtime power management on ipw2100 Date: Wed, 31 Jan 2007 09:48:58 +0000 Message-ID: <20070131094858.GA23842@srcf.ucam.org> References: <20070131075249.GA22115@srcf.ucam.org> <1170234787.6746.22.camel@amit-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: ipw2100-devel@lists.sourceforge.net, linux-pm@lists.osdl.org, netdev@vger.kernel.org To: Amit Kucheria Return-path: Content-Disposition: inline In-Reply-To: <1170234787.6746.22.camel@amit-laptop> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: ipw2100-devel-bounces@lists.sourceforge.net Errors-To: ipw2100-devel-bounces@lists.sourceforge.net List-Id: netdev.vger.kernel.org On Wed, Jan 31, 2007 at 11:13:07AM +0200, Amit Kucheria wrote: > What is the latency in changing between different PCI power states for > peripherals? I'm not sure in the general case, but the power-down path for the ipw2100 involves a static wait of 100ms in ipw2100_hw_stop_adapter(). > Would it be possible e.g. to put the peripheral into a low power state > after each Tx/Rx (with reasonable hyteresis)? Most wireless drivers support some degree of power management at this scale, but (in ipw2100 at least) it's implemented in the firmware so I have absolutely no idea what it's actually doing. > > > > The situation is slightly more complicated for wired interfaces. As > > previously discussed, we potentially want three interface states (on, > > low power, off) with the intermediate one powering down as much of the > > hardware as possible while still implementing link detection. > > And this low power state is what the HW should be in all the time, > except when it has work to do. PCI seems to require a delay of 10ms when sequencing from D3 to D0, which probably isn't acceptable latency for an "up" state. While there's definitely a benefit to the sort of PM you're describing (it's a model we've already started using on the desktop as far as the CPU goes), I think we still want to be able to expose as much power saving as possible. -- Matthew Garrett | mjg59@srcf.ucam.org ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV