linux-kernel - Re: New 'make dtbs

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Message-ID: <20210413023612.GH1538589@yoga>
Date:   Mon, 12 Apr 2021 21:36:12 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        DTML <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linusw@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Kevin Hilman <khilman@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Tony Lindgren <tony@...mide.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Nishanth Menon <nm@...com>, Tero Kristo <kristo@...nel.org>,
        SoC Team <soc@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: New 'make dtbs_check W=1' warnings

On Mon 12 Apr 13:52 CDT 2021, Arnd Bergmann wrote:

> On Mon, Apr 12, 2021 at 6:01 PM Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> > On Mon 12 Apr 08:14 CDT 2021, Arnd Bergmann wrote:
> > > On Mon, Apr 12, 2021 at 1:32 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > > > On Thu, Apr 8, 2021 at 5:08 PM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > So the same binding patch is picked up both in the driver and soc tree?
> > I was expecting that to cause (harmless) conflicts when things arrive in
> > Linus' merge queue?
> >
> > Or are you saying people go the length to create immutable branches for
> > each binding?
> 
> I think it's usually one immutable branch for all the bindings of a given
> merge window. This avoids the merge conflicts, and you can add further
> bindings on the same branch before sending it off to the soc tree.
> 

That would be convenient to have, but the binding changes we depend on
in a given window (in particular if dtbs_check is expected to pass) is
scattered over a wide range of maintainer trees.

> > I'm curious because it's fairly often that we introduce clocks,
> > interconnects etc where the macros from the dt bindings includes aren't
> > available for another release (so we use numerical constants and then go
> > back and fix them up later).
> 
> Ah right, it is particularly bad for platforms that don't have a regular
> layout in these blocks and need to define a new constant every time
> another clock/reset/pin/... is discovered in the downstream sources.
> 

Even blocks following some standardized layout has this problem, because
each platform will have it's own (often similar) set of
clocks/resets/pins.

And going back to dtbs_check, you will continue to see the warnings
about missing compatibles, because most of the case they won't end up in
the soc tree.

> I was mainly referring to the simpler problem of defining a binding
> document for a device once, and then merging the nodes.
> 

I'm sure we all love the hardware that's simple to translate to a DT
binding, unfortunately though we're dealing with complex SoCs.

Regards,
Bjorn