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

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Message-ID: <000b01d35fc1$57ad0500$07070f00$@gmail.com>
Date:   Fri, 17 Nov 2017 11:30:09 -0500
From:   "Jingoo Han" <jingoohan1@...il.com>
To:     "'Pavel Machek'" <pavel@....cz>, "'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>
Subject: Re: [PATCH v3 1/2] dt: bindings: lm3692x: Add bindings for lm3692x LED driver

On Friday, November 17, 2017 6:21 AM, Pavel Machek wrote:
> 
> 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 also agree with your opinion.

Best regards,
Jingoo Han

> 
> > 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