From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: Change uevent whenever brightness is set to 0 Date: Tue, 04 Aug 2015 12:52:28 +0200 Message-ID: <55C0996C.6020905@gmail.com> References: <5500469A22567C4BAF673A6E86AFA3A40227C1D640EC@IR-CENTRAL.corp.innerrange.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-wi0-f175.google.com ([209.85.212.175]:34216 "EHLO mail-wi0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932331AbbHDKwb (ORCPT ); Tue, 4 Aug 2015 06:52:31 -0400 Received: by wibud3 with SMTP id ud3so171343889wib.1 for ; Tue, 04 Aug 2015 03:52:30 -0700 (PDT) In-Reply-To: <5500469A22567C4BAF673A6E86AFA3A40227C1D640EC@IR-CENTRAL.corp.innerrange.com> Sender: linux-leds-owner@vger.kernel.org List-Id: linux-leds@vger.kernel.org To: Craig McQueen , "linux-leds@vger.kernel.org" Hi Craig, On 08/04/2015 05:56 AM, Craig McQueen wrote: > I've written a udev rule to catch uevent "change" events, with the goal of setting LED user/group/permissions whenever trigger settings are changed. > > http://unix.stackexchange.com/a/202870/34376 > > However, I've noticed that a TRIGGER uevent "change" event is generated every time an LED is turned off. > > E.g. in one terminal: > udevadm monitor -p > > In another terminal: > echo 0 > /sys/class/leds/beaglebone:green:usr3/brightness > > The first terminal shows: > > KERNEL[15446.374466] change /devices/leds/leds/beaglebone:green:usr3 (leds) > ACTION=change > DEVPATH=/devices/leds/leds/beaglebone:green:usr3 > SEQNUM=39147 > SUBSYSTEM=leds > TRIGGER=none > > This behaviour is not ideal, because I really only want this uevent if the trigger really has changed. > > I presume this is due to these two lines in brightness_store() in led-class.c: > if (state == LED_OFF) > led_trigger_remove(led_cdev); > > What would be the recommended way to improve this, so a TRIGGER uevent "change" event is only generated if the trigger is actually reset to 'none' in this scenario? > > I've noticed this on kernel 3.14.48 running on BeagleBone Black. > You can define your rule so that it would not be matched when TRIGGER=none. -- Best Regards, Jacek Anaszewski