linux-kernel - Re: [PATCH v3 1/3] of: Support parsing phandle argument lists through a nexus node

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Date:   Thu, 09 Feb 2017 11:55:21 -0800
From:   Stephen Boyd <stephen.boyd@...aro.org>
To:     Rob Herring <robh+dt@...nel.org>,
        "Russell King - ARM Linux" <linux@...linux.org.uk>
Cc:     "Frank Rowand" <frowand.list@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Pantelis Antoniou" <pantelis.antoniou@...sulko.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "Mark Brown" <broonie@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 1/3] of: Support parsing phandle argument lists through a
 nexus node

Quoting Rob Herring (2017-02-09 08:00:05)
> On Thu, Feb 9, 2017 at 9:35 AM, Russell King - ARM Linux
> <linux@...linux.org.uk> wrote:
> > On Thu, Feb 09, 2017 at 09:17:58AM -0600, Rob Herring wrote:
> >> Frank, any more comments on this? If not, I plan to apply this series.
> >
> > Well, I find that a little annoying, because DT has the requirement
> > that new bindings are properly documented in Documentation, and it
> > appears that this comes with no documentation what so ever, despite
> > introducing new properties (like the -map-mask-passthru thing).
> >
> > So I'm NAKing it until there's some documentation of how this
> > mechanism is supposed to work.
> >
> > Merely providing an example in a commit log is (IMHO) insufficient.
> > An example doesn't explain how it was created, or how to create an
> > implementation.
> 
> Yes, you are right.
> 
> However, I'd like to see this documented in the DT spec, rather than
> kernel Documentation/ as this is a core binding. Though that would
> also imply first moving the GPIO bindings there. Perhaps just how this
> works generically could be in the spec, but the GPIO specifics can
> live with the rest of the GPIO bindings for now. This is intended to
> extend to other bindings.

I will make a patch against the devicetree spec and send it as a reply
to this series.

> 
> > Remember, we expect people to do exactly that, so we need to give
> > them this information so that they can make use of it.
> >
> > I did try to work out from the code how the -map-mask thing worked,
> > but eventually gave up.
> 
> The code is definitely hard to follow and I've not come up with any
> ways to make it easier to read. It's largely copied from the
> interrupt-map version, but different enough that sharing isn't really
> possible either.
> 
> For interrupts, it's documented in the DT spec. The best (only?)
> explanation for how interrupt-map works is here[1] (used to be at
> devicetree.org).
> 

interrupt-map is also documented in the latest DT spec[2]. I can add
another section for "Generic Nexus Properties" and describe how this
code works.

[2] http://www.devicetree.org/specifications-pdf