Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755755Ab0F0TyM (ORCPT ); Sun, 27 Jun 2010 15:54:12 -0400 Received: from opensource.wolfsonmicro.com ([80.75.67.52]:38788 "EHLO opensource2.wolfsonmicro.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754762Ab0F0TyJ convert rfc822-to-8bit (ORCPT ); Sun, 27 Jun 2010 15:54:09 -0400 Subject: Re: [PATCH v3 1/4] hwmon: Driver for SMM665 Six-Channel Active DC Output Controller/Monitor Mime-Version: 1.0 (Apple Message framework v1081) Content-Type: text/plain; charset=us-ascii From: Mark Brown In-Reply-To: <20100627151047.GA5731@ericsson.com> (sfid-20100627_161157_396817_8F10F51C) Date: Sun, 27 Jun 2010 20:54:06 +0100 Cc: Randy Dunlap , Jean Delvare , Andrew Morton , "Ira W. Snyder" , Hans de Goede , Samuel Ortiz , Jonathan Cameron , "lm-sensors@lm-sensors.org" , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" Content-Transfer-Encoding: 8BIT Message-Id: <52840892-BE40-44D3-9454-407B074481CC@opensource.wolfsonmicro.com> References: <1277416861-32494-1-git-send-email-guenter.roeck@ericsson.com> <1277416861-32494-2-git-send-email-guenter.roeck@ericsson.com> <20100627102058.GB2845@sirena.org.uk> <20100627151047.GA5731@ericsson.com> (sfid-20100627_161157_396817_8F10F51C) To: Guenter Roeck X-Mailer: Apple Mail (2.1081) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2149 Lines: 43 On 27 Jun 2010, at 16:10, Guenter Roeck wrote: > On Sun, Jun 27, 2010 at 06:20:59AM -0400, Mark Brown wrote: >> A bit late to the game here but this looks like the chip has some >> regulator control functionality as well as monitoring functionality (and >> the product page on the Summit web site suggests so also). This means >> that when fully supported in software the driver would cross multiple >> subsystems so it might make sense to start off with a MFD rather than >> direct I2C control? >> >> If the non-monitoring functionality can't be controlled from software >> this isn't an issue. > > I thought about that when I started working on the driver, but concluded that > it does not really make sense. > > The chip is commonly used to control all supply voltages on a board. > Changing those voltages is not a good idea. For that reason, the chip can be There's rather a lot of systems out there doing DVFS or using things like MMC cards which would disagree with the idea that it's a bad idea to change supply voltages at runtime. Even for fixed voltage supplies enabling and disabling at runtime is useful to save power. I think it's fair to say that the overall trend is towards more dynamic power management. > set into read-only mode, where changing the voltages is no longer possible > after initial programming. This tends to be done through paranoia more than anything else - people get very worried about things like accidental writes to their PMICs. > While it is theoretically possible that someone might use the device to control > not only fixed but also dynamic voltages, I think that is highly unlikely, given > the risk involved in blowing up the board. Thus, moving the driver to mfd would > effectively serve no real purpose other than to cause confusion and add unnecessary Pretty much any current generation CPU can use dynamic voltage configuration for DVFS.-- 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/