linux-kernel - Re: [PATCH] Enable backlight when trigger is activated

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Date:   Mon, 22 Jul 2019 09:50:32 +0200
From:   Pavel Machek <pavel@....cz>
To:     Ezequiel Garcia <ezequiel@...labora.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, tony@...mide.com, sre@...nel.org,
        nekit1000@...il.com, mpartap@....net, merlijn@...zup.org,
        jacek.anaszewski@...il.com, linux-leds@...r.kernel.org,
        b.zolnierkie@...sung.com, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org
Subject: Re: [PATCH] Enable backlight when trigger is activated

Hi!

> > Configuring backlight trigger from dts results in backlight off during
> > boot. Machine looks dead upon boot, which is not good.
> > 
> > Fix that by enabling LED on trigger activation.

> > +++ b/drivers/leds/trigger/ledtrig-backlight.c
> > @@ -114,6 +114,8 @@ static int bl_trig_activate(struct led_classdev *led)
> >  	n->old_status = UNBLANK;
> >  	n->notifier.notifier_call = fb_notifier_callback;
> >  
> > +	led_set_brightness(led, LED_ON);
> > +
> 
> This looks fishy.
> 
> Maybe you should use a default-state = "keep" instead? (and you'll have
> to support it in the LED driver).
> 
> That'll give you proper "don't touch the LED if it was turned on" behavior,
> which is what you seem to want.

Actually no, that's not what I want. LED should go on if the display
is active, as soon as trigger is activated.

Unfortunately, I have see no good way to tell if the display is
active (and display is usually active when trigger is activated).

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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