linux-kernel - Re: [RFC PATCH 0/5] leds: Add DT node finding and parsing to core

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Date:   Tue, 19 Nov 2019 20:52:04 +0100
From:   "Enrico Weigelt, metux IT consult" <info@...ux.net>
To:     "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>,
        "mazziesaccount@...il.com" <mazziesaccount@...il.com>
Cc:     "dmurphy@...com" <dmurphy@...com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pavel@....cz" <pavel@....cz>,
        "linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
        "jacek.anaszewski@...il.com" <jacek.anaszewski@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
Subject: Re: [RFC PATCH 0/5] leds: Add DT node finding and parsing to core

On 18.11.19 11:38, Vaittinen, Matti wrote:

Hi,

>> a) existing DT's (in the field) become incompatible with newer
>>    kernel versions
> 
> This was my main concern. This of course would not mean that we could
> not take this approach for new LED controller drivers - but that would
> (probably) lead to dual led registration interface 

Maybe just a flag for that ? Perhaps the driver could also specify a
list of node names for the LEDs, so led-core can do the lookup for them.

>> b) existing userlands that rely on speicific LED names become
>>    incomatible with newer kernel versions.
> 
> I didn't even think this far, but yes, I see... LED node name might be
> reflected in user-space LED name. I won't start arguing if this is sane
> or not - this is what we seem to be living with today :)

Especially in embedded world, this can really make sense: applications
just use a defined LED name, no matter which board it's running on.
Convention over configuration.

Personally, I also like to use LED subsystem as frontend for things like
gpio-driven relais, etc, and assign semantically fitting names instead
of "technical" ones,

> I didn't invest too much of time on this yet - but at first glimpse it
> seemed that at least some of the drivers did use reg - property with
> fixed value to do the matching. Those could set the property name to
> 'reg' and value to 'X' and leave the DT node lookup and common property
> parsing to the LED core. If my patch won't get too big objection (and
> if no fatal flaws are found from the idea) - then I might try and find
> the time to do some follow-up patches simplifying existing LED
> drivers...

Sounds good :)


--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287