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

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Date:   Thu, 16 Nov 2017 21:14:13 +0100
From:   Jacek Anaszewski <jacek.anaszewski@...il.com>
To:     Pavel Machek <pavel@....cz>, Dan Murphy <dmurphy@...com>
Cc:     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 Dan and Pavel,

On 11/15/2017 11:23 PM, Pavel Machek wrote:
> Hi!
> 
>>> Shouldn't the driver be targeted for backlight subsystem then?
>>>
>>> Adding backlight maintainers.
>>>
>>
>> Great point!  I was not aware of the backlight subsystem.
>>
>> Looks like I need to create a back light version as well.
>>
>> Like the lp8788 did since this can be used as a LED driver beyond
>> display back lighting.
> 
> No, definitely not two drivers for lp8788 hardware.

I agree.

> 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"?

As a side note I can say that I've been always wondering why the two
subsystems for similar type of hardware.

-- 
Best regards,
Jacek Anaszewski