From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966378Ab2ERR5t (ORCPT ); Fri, 18 May 2012 13:57:49 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:58104 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965071Ab2ERR5q (ORCPT ); Fri, 18 May 2012 13:57:46 -0400 Date: Fri, 18 May 2012 19:57:42 +0200 From: Johan Hovold To: Jonathan Cameron Cc: Johan Hovold , Jonathan Cameron , Rob Landley , Richard Purdie , Samuel Ortiz , Greg Kroah-Hartman , Florian Tobias Schandinat , Arnd Bergmann , Andrew Morton , Mark Brown , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org, devel@driverdev.osuosl.org, linux-fbdev@vger.kernel.org Subject: Re: [PATCH v2 2/4] iio: add LM3533 ambient light sensor driver Message-ID: <20120518175742.GA12894@localhost> References: <1336040799-18433-3-git-send-email-jhovold@gmail.com> <4FA26E9A.8080209@cam.ac.uk> <20120503163617.GD15752@localhost> <4FA923E7.6050707@cam.ac.uk> <20120515164456.GB15632@localhost> <4FB2B5EE.6080009@kernel.org> <20120516130507.GA10774@localhost> <4FB3B7DA.5050306@cam.ac.uk> <20120518122725.GB20467@localhost> <4FB68809.2010009@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FB68809.2010009@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 18, 2012 at 06:34:01PM +0100, Jonathan Cameron wrote: > On 05/18/2012 01:27 PM, Johan Hovold wrote: [...] > > I really think that this should remain a device specific attribute as I > > originally suggested. It's an integration parameter that needs to be set > > precisely depending on the actual hardware setup (which analog light > > sensor and other external components). > Then it shouldn't be exposed to userspace. If there is reason to vary > it from userspace then it is a calibration parameter and should be > treated like the other ones we have, if not it should be done from > dt or platform data. > > > > The lm3533 also supports two types of light sensors: pwm- and analog- > > output ones. The resistor select settings only applies when in analog > > mode as the input is always high impedance otherwise. Thus a generic > > attribute (such as calibscale or hardware gain) shouldn't be used as it > > will have no effect whatsoever in PWM-mode. > > > > I'm thus back at my original proposal, albeit with a different name (I > > think a lot of this discussion could have been avoided had I not > > misnamed the parameter "gain"): > > > > What: /sys/bus/iio/devices/iio:deviceX/r_select > > Description: > > Set the ALS internal pull-down resistor for analog input mode > > (1..127), such that, > > > > R_als = 200000 / r_select (ohm) > > > > This setting is ignored in PWM-mode (input is always high > > impedance in PWM-mode). > > > > I don't think much is gained from using ohm as the unit: it just adds > > complexity and the selected resistor setting will likely not match the > > input value anyway. It's better that the chip integrators have full > > control over which resistor setting is actually used so that it matches > > external components. > This smacks of something that should never be exposed to users. > I'd hide it away in platform data. Fair enough. I'll drop the sysfs param and submit a patch for mfd-next which adds r_select to the platform data. Thanks, Johan