linux-kernel - Re: [PATCH] dt-bindings: Add bindings for aliases node

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Message-ID: <1626442.UsWqDEgn3j@debian64>
Date:   Fri, 12 Oct 2018 18:31:11 +0200
From:   Christian Lamparter <chunkeey@...il.com>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Brian Norris <briannorris@...omium.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, swboyd@...omium.org,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH] dt-bindings: Add bindings for aliases node

On Friday, October 12, 2018 2:08:37 AM CEST Matthias Kaehlcke wrote:
> Maybe the doc should include a recommendation to use aliases
> sparingly? I'm open to input on that from folks who have a better
> understanding of the potential pitfalls 

I had a similar discussion with the OpenWrt devs over the
use of "led-$function" aliases in a DTS. I did a bit of digging and
found this wonderful emails from Mark Rutland regarding the general
use and abuse of aliases in a reply to a patch by Christer Weinigel 
"devicetree - document using aliases to set spi bus number."

<https://patchwork.kernel.org/patch/9133903/#19207021>

|"If those ports are physically organised and labelled the same, then
|using aliases could make sense, to describe the well-defined physical
|labels. If you've assigned the numbers artificially, or if the physical
|organisation differs across boards, then aliases are not the right tool
|for the job.
|
|In the latter cases we're altering the hardware description to suit an
|application, rather than providing the necessary abstraction, which is
|the kind of (ab)use of aliases which we want to avoid."

And he followed it up with a summary:
<https://patchwork.kernel.org/comment/19207071/>

|Typically, serial ports are much more user-accessible (physically), and
|much more directly useful to a user in a generic fashion. They're often
|labelled (physically or in a manual) with a number, and we use aliases
|to describe those labels to the kernel. The fact that the kernel may use
|that to drive its own internal numbering is immaterial to the binding.

So the gist of this is that aliases are meant for user-accessible /
physically devices/ports/etc... that are labeled as such. And this of
course works perfectly for power/status LEDs and such because they
usually have little "power" symbols/pictograms/lables near them.