linux-kernel - Re: [PATCH v4 2/2] leds: bd2606mvv: Driver for the Rohm 6 Channel i2c LED driver

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Date:   Sat, 15 Apr 2023 10:01:02 +0200
From:   Pavel Machek <pavel@....cz>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     lee@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matti Vaittinen <mazziesaccount@...il.com>
Subject: Re: [PATCH v4 2/2] leds: bd2606mvv: Driver for the Rohm 6 Channel
 i2c LED driver

Hi!

> > > The device provides 6 channels which can be individually
> > > turned off and on but groups of two channels share a common brightness
> > > register.  
> > 
> > Yeah, well.. Turn it into 3-channel controller with brightness or
> > 6-channel on/off one... You can't really share brightness.
> > 
> No, I cannot change the hardware, so it is a 6-channel with limitations.
> And the devicetree has to describe the hardware and not the driver.

Device tree is okay, I commented on the driver.

> What is discussable is just how the driver should deal with that:
> 
> I see 5 possibilities.
> a) ignore the shared brightness problem (status quo)
> b) never set a brightness other than full on/off
> c) ignore one led of each pair (not register it at all{
> d) couple also the on/off of the pairs, so present to
>    userspace only max. 3 leds.
> e) allow full brightness control where independently possible,
>    if LEDs are defined where that leads to conflicts,
>    register them with max_brightness=1 and use them
>    in on/off mode.
> 
> My preference were a) or e), the most possible usages.
> e) has a cleaner interface to the userspace.

b) c) e) are acceptable to me. So I guess e) is preffered.

BR,							Pavel
-- 
People of Russia, stop Putin before his war on Ukraine escalates.

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