From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacek Anaszewski Subject: Re: Switching off LED triggers udev Date: Mon, 10 Apr 2017 20:42:23 +0200 Message-ID: References: <1803981.yiQbQ3iWBI@sherry> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Return-path: Received: from mail-wr0-f196.google.com ([209.85.128.196]:33340 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751273AbdDJSnI (ORCPT ); Mon, 10 Apr 2017 14:43:08 -0400 Received: by mail-wr0-f196.google.com with SMTP id l28so5485951wre.0 for ; Mon, 10 Apr 2017 11:43:08 -0700 (PDT) In-Reply-To: <1803981.yiQbQ3iWBI@sherry> Sender: linux-leds-owner@vger.kernel.org List-Id: linux-leds@vger.kernel.org To: schindele@nentec.de, linux-leds@vger.kernel.org Hi Juergen. On 04/10/2017 04:29 PM, Juergen Schindele wrote: > Hello List, > i hope i found the right addres for this small problem. > I have a userspace daemon which controls leds via sysfs API > "/sys/class/leds/Soft1/brightness". Each time i turn the LED off > by writing 0 to brightness the /proc/sys/kernel/hotplug deamon > is called with "ACTION:change SUBSYSTEM:leds DEVNAME:(null) > DEVPATH:/devices/...." > > from led-class.c ---------------------------- > if (state == LED_OFF) > led_trigger_remove(led_cdev); > __led_set_brightness(led_cdev, state); > > But in fact there is no change of trigger because "none" was setup between > enabling LED and disabling it. So from my point of view there is no change > from "none" to "remove" which justifies a "kobject_uevent_env(&led_cdev->dev- >> kobj, KOBJ_CHANGE, envp)". > > To solve this problem of unusefull waste of CPU-time i suggest the following > patch. Please consider the implementation which saved a lot of valuable CPU- > power in my case: > > Index: drivers/leds/led-triggers.c > =================================================================== > --- drivers/leds/led-triggers.c (Revision 14968) > +++ drivers/leds/led-triggers.c (Arbeitskopie) > @@ -106,10 +106,11 @@ > const char *name; > > name = trig ? trig->name : "none"; > - event = kasprintf(GFP_KERNEL, "TRIGGER=%s", name); > > /* Remove any existing trigger */ > if (led_cdev->trigger) { > + event = kasprintf(GFP_KERNEL, "TRIGGER=%s", name); > + > write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, > flags); > list_del(&led_cdev->trig_list); > write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock, > @@ -122,6 +123,8 @@ > led_set_brightness(led_cdev, LED_OFF); > } > if (trig) { > + event = kasprintf(GFP_KERNEL, "TRIGGER=%s", name); > + > write_lock_irqsave(&trig->leddev_list_lock, flags); > list_add_tail(&led_cdev->trig_list, &trig->led_cdevs); > write_unlock_irqrestore(&trig->leddev_list_lock, flags); > > Thank you for your attention In 4.9 we have the following patch that should fix your problem, please let us know if it works for you: commit fbfa197afddd13f9bdca1c822f5d5730b50639eb Author: Jacek Anaszewski Date: Sun Sep 18 20:24:29 2016 +0200 leds: triggers: Return from led_trigger_set() if there is nothing to do If led_trigger_set() is called with "trig" argument set to NULL, and there is no trigger to remove then the function should return immediately so as to avoid doing unnecessary allocation and sending uevent. Signed-off-by: Jacek Anaszewski Reported-by: Daniel Romell Acked-by Daniel Romell diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c index 59d6a3e..c7a38d4 100644 --- a/drivers/leds/led-triggers.c +++ b/drivers/leds/led-triggers.c @@ -110,6 +110,9 @@ void led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig) char *envp[2]; const char *name; + if (!led_cdev->trigger && !trig) + return; + name = trig ? trig->name : "none"; event = kasprintf(GFP_KERNEL, "TRIGGER=%s", name); -- Best regards, Jacek Anaszewski