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

From: Christian Lamparter
Date: Fri Oct 12 2018 - 12:31:21 EST

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."


|"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:

|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.