On Sat, 08 Mar 2025 04:10:49 +1100 Jacek Anaszewski wrote:
> On 3/7/25 17:50, Jacek Anaszewski wrote:
> > Hi Craig,
> >
> > On 3/6/25 23:55, Craig McQueen wrote:
> >> If the text "default" is written to the LED's sysfs 'trigger' attr, then
> >> call led_trigger_set_default() to set the LED to its default trigger.
> >> ---
> >> drivers/leds/led-triggers.c | 5 +++++
> >> 1 file changed, 5 insertions(+)
> >>
> >> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> >> index b2d40f87a5ff..f2bc3bb5062d 100644
> >> --- a/drivers/leds/led-triggers.c
> >> +++ b/drivers/leds/led-triggers.c
> >> @@ -54,6 +54,11 @@ ssize_t led_trigger_write(struct file *filp, struct
> >> kobject *kobj,
> >> goto unlock;
> >> }
> >> + if (sysfs_streq(buf, "default")) {
> >> + led_trigger_set_default(led_cdev);
> >> + goto unlock;
> >> + }
> >> +
> >> down_read(&triggers_list_lock);
> >> list_for_each_entry(trig, &trigger_list, next_trig) {
> >> if (sysfs_streq(buf, trig->name) &&
> >> trigger_relevant(led_cdev, trig)) {
> >
> > Makes sense for me, this would be the second half of the feature that is
> > now available only from DT level.
> >
> > Reviewed-by: Jacek Anaszewski jacek.anaszewski@xxxxxxxxx>
> >
>
> But after re-thinking it - we need to return -EINVAL in case
> LED class device does not define default trigger, so that the user
> had proper feedback.
>
> So, led_trigger_set_default() needs to be extended to return error
> in case of !led_cdev->default_trigger or !found.
In systems I've worked on, some LEDs have a default trigger, while others don't. I.e. it seems normal for an LED to have a default trigger of "none". I don't think of this as an error condition, but a normal operation to set an LED's trigger back to "none".
The not-found case is an interesting corner case. It might be that a kernel module that provides a trigger is presently not loaded, so the trigger is not currently available -- but will be available if the kernel module is loaded again.
1. LED has a default trigger "moduletrigger".
2. Module that provides that trigger "moduletrigger" is unloaded.
3. LED has trigger set to something else, "othertrigger".
4. led_trigger_set_default() is called for that LED.
Will the LED's trigger be effectively "none", or stay at "othertrigger"?
5. Module that provides "moduletrigger" is loaded again.
Will the LED be connected to its default trigger "moduletrigger", or remain at "none"?
--
Craig McQueen
