Re: Switching off LED triggers udev

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Am Montag, 10. April 2017, 20:42:23 schrieben Sie:
Hello Jacek,
that is a good hint. Yes the effect is the same and it works great too
for me. I was not looking to the most recent kernel sorry.
Thank you for your help
> 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_lo
> >                 ck,
> > 
> > @@ -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 <jacek.anaszewski@xxxxxxxxx>
> 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 <j.anaszewski@xxxxxxxxxxx>
>     Reported-by: Daniel Romell <daro@xxxxxx>
>     Acked-by Daniel Romell <daro@xxxxxx>
> 
> 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);

-- 
i. A.
Jürgen Schindele
Softwareentwicklung

PSI Nentec GmbH
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