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

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Date:   Wed, 20 Nov 2019 07:37:42 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "info@...ux.net" <info@...ux.net>
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 Tue, 2019-11-19 at 20:52 +0100, Enrico Weigelt, metux IT consult
wrote:
> 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.

This is actually close to what I suggested in my other email to Jacek.

> > > 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.

Definitely. I am all for generating the name based on LED _function_ -
no matter what the board is. I like the LED name generation base on
'function' DT property. But node names tend to be somewhat generic - or
board specific (to avoid collisions). So using node name directly is
not (as far as my understanding goes - which is limited on this topic)
optimal for guaranteeing coherent view (across the boards) for user-
space. Wow, what a nice sentence for non native English speaker like me
xD

> 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,

This is outside of my experience so I just believe what you say :)

> 
> > 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
>