linux-kernel - Re: [PATCH v3 1/2] dt: bindings: lm3692x: Add bindings for lm3692x LED driver

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Date:   Fri, 17 Nov 2017 12:20:32 +0100
From:   Pavel Machek <pavel@....cz>
To:     Dan Murphy <dmurphy@...com>
Cc:     Jacek Anaszewski <jacek.anaszewski@...il.com>, robh+dt@...nel.org,
        mark.rutland@....com, rpurdie@...ys.net,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org, Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>
Subject: Re: [PATCH v3 1/2] dt: bindings: lm3692x: Add bindings for lm3692x
 LED driver

Hi!

> >> If that does not yet exist... you want to create glue layer to be able
> >> to use LED as a display backlight. (It may already exist, no idea).
> >>
> >> ...
> >>
> >> Actually or maybe a LED trigger. Just set LED's trigger to "this is
> >> display backlight".
> > 
> > There is one already:
> > 
> > drivers/leds/trigger/ledtrig-backlight.c
> > 
> > It adds a LED class device to the fb_notifier_list
> > (drivers/video/fbdev/core/fb_notify.c)
> > 
> > using fb_register_client(). The same is used in
> > backlight_device_register (drivers/video/backlight/backlight.c).
> > 
> > Actually why do you want to have this driver in the LED subsystem,
> > if it is advertised as "designed for LCD display backlighting"?
> 
> Well this is also advertised as a driver for Smart phone and tablet devices.  And having worked with the Android lighting
> solutions this is the preferred subsystem for Android.  The Android OS manages the led brightness based on ALS values and in
> turn calls into the driver to control the brightness register through the vendor provided lighting HAL.
> 

Well.. if it can control other LEDs than just backlight, I believe it
can stay in the LED subsystem.

> I am going to look at the backlight source to figure out how to get the same functionality using the backlight subsystem.
> Otherwise I will plug in this driver to the backlight subsystem through the notifier.
> 

The backlight trigger should be ok.

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

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