Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760615Ab0HLUsQ (ORCPT ); Thu, 12 Aug 2010 16:48:16 -0400 Received: from wolverine01.qualcomm.com ([199.106.114.254]:36874 "EHLO wolverine01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754962Ab0HLUsN (ORCPT ); Thu, 12 Aug 2010 16:48:13 -0400 X-IronPort-AV: E=McAfee;i="5400,1158,6072"; a="50821668" Date: Thu, 12 Aug 2010 13:48:11 -0700 From: David Brown To: Russell King - ARM Linux Cc: Gregory Bean , linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tsoni@qualcomm.com Subject: Re: [RFC] the right way to use gpiolib hooks to automate power management? Message-ID: <20100812204811.GA31315@huya.qualcomm.com> References: <4C6423C1.9060509@codeaurora.org> <20100812182744.GC31982@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100812182744.GC31982@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1274 Lines: 26 On Thu, Aug 12, 2010 at 07:27:44PM +0100, Russell King - ARM Linux wrote: > On Thu, Aug 12, 2010 at 09:39:29AM -0700, Gregory Bean wrote: > > We have a written a software driver which reference-counts these gpio > > lines (via a put()/get() api), putting them in their "high-power" active > > configurations when they're in use, and dropping them down into a > > high-impedance low-power setting when they're not. > > Beware. What you're suggesting can lead to an increase in power > consumption rather than the reduction you're looking for. That probably just got a little obscured, since I think Greg is more concerned with the mechanism in software. Our gpio's are generally configured in "low power" to be high-impedance with a pull-up or pull-down, depending on what it is hooked to. They can be configured in most of the ways that would make sense to do so. It may be the case, though, that what this "low power" mode is might need to also be configurable, since it likely depends on how the pin is connected. David -- 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/