From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760963Ab2CPQF2 (ORCPT ); Fri, 16 Mar 2012 12:05:28 -0400 Received: from Mycroft.westnet.com ([216.187.52.7]:60372 "EHLO mycroft.westnet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752733Ab2CPQF0 (ORCPT ); Fri, 16 Mar 2012 12:05:26 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <20323.25792.171143.809563@quad.stoffel.home> Date: Fri, 16 Mar 2012 12:05:20 -0400 From: "John Stoffel" To: simon@mungewell.org Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Building BarGraph with LED subsystem In-Reply-To: <1b29a178dd288b0f17608b5815ca77a5.squirrel@mungewell.org> References: <1b29a178dd288b0f17608b5815ca77a5.squirrel@mungewell.org> X-Mailer: VM 8.1.2 under 23.2.1 (x86_64-pc-linux-gnu) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org simon> I have a couple of questions about the (user-land) use of the simon> LED subsystem. simon> I recently offered a patch for controlling the LEDs of the G27 gaming simon> wheel, on which the LEDs are arranged in a bar-graph of 5 to show simon> simulation RPM. The suggestion was to use the LED subsystem, which this simon> patch implements. simon> http://www.spinics.net/lists/linux-input/msg19747.html simon> Thinking further about how to about how to control this I was wondering simon> whether a 'threshold' trigger would be useful. This would allow the use of simon> value (uint?) to be compare against a threshold and the LED turned on/off simon> automatically. simon> The main benefit of doing this as a 'trigger' is that we could 'link' (or simon> 'sync') multiple LEDs to use the same value input, thus making the simon> user-land stuff trivial. While making the kernel more complex... esp for a feature which is of such limited use. Do it all in userland, it's easier, you can use floating point math, etc. And to test changes, you don't have to recompile a module and unload/reload it, etc. Keeping as much of this in userland is better. simon> Also I have a question about the default permissions on the LED simon> controls; Is it possible to register LEDs so that users have simon> write permission? At present the controls are only accessible simon> as root. udev is the answer here. You probably want to make it so that the LEDs are open to the user logged into the system console or currently active Xsession. John