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

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Message-ID: <f00d99cb-da32-05b3-bf49-447cb8bd33e0@gmail.com>
Date:   Wed, 24 Jul 2019 23:16:39 +0200
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Ezequiel Garcia <ezequiel@...labora.com>,
        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,
        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

On 7/24/19 10:33 AM, Pavel Machek wrote:
> Hi!
> 
>>>>> +++ 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).
>>
>> default-state DT property can be also set to "on"
>> (see Documentation/devicetree/bindings/leds/common.txt).
> 
> Yes, except that it does not work with all drivers :-(. In particular,
> it does not work with lm3532.
> 
> We should really move more of the device tree parsing into core, so
> that there's one place to fix...

Right. We could have something similar to led_get_default_pattern().
led_get_default_state() ?

-- 
Best regards,
Jacek Anaszewski