Message-ID: <20200119063916.GD54439@umbus>
Date:   Sun, 19 Jan 2020 16:39:16 +1000
From:   David Gibson <david@...son.dropbear.id.au>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Alexandre Torgue <alexandre.torgue@...com>,
        Frank Rowand <frowand.list@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Simon Glass <sjg@...omium.org>, devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Devicetree Compiler <devicetree-compiler@...r.kernel.org>,
        Steve McIntyre <steve.mcintyre@...aro.org>
Subject: Re: [RFC PATCH 1/3] dtc: Add dtb build information option

On Fri, Jan 17, 2020 at 08:43:23AM -0600, Rob Herring wrote:
> On Fri, Jan 17, 2020 at 6:26 AM David Gibson
> <david@...son.dropbear.id.au> wrote:
> >
> > On Thu, Jan 16, 2020 at 09:58:23AM +0100, Alexandre Torgue wrote:
> > > Hi David
> > >
> > > On 1/16/20 1:57 AM, David Gibson wrote:
> > > > On Mon, Jan 13, 2020 at 07:16:23PM +0100, Alexandre Torgue wrote:
> > > > > This commit adds the possibility to add build information for a DTB.
> > > > > Build information can be: build date, DTS version, "who built the DTB"
> > > > > (same kind of information that we get in Linux with the Linux banner).
> > > > >
> > > > > To do this, an extra option "-B" using an information file as argument
> > > > > has been added. If this option is used, input device tree is appended with
> > > > > a new string property "Build-info". This property is built with information
> > > > > found in information file given as argument. This file has to be generated
> > > > > by user and shouldn't exceed 256 bytes.
> > > > >
> > > > > Signed-off-by: Alexandre Torgue <alexandre.torgue@...com>
> > > >
> > > > At the very least, this patch of the series will need to be sent to
> > > > upstream dtc first.
> > >
> > > Ok sorry. I thought that sending all the series would give more
> > > information.
> >
> > That's fair enough, but in order to merge, you'll need to post against
> > upstream dtc.
> >
> > > > I'm also not terribly clear on what you're trying to accomplish here,
> > > > and why it's useful.
> > >
> > > Let's take Kernel boot at example (but could be extend to other DTB "users"
> > > like U-Boot). When Linux kernel booting we get a log that gives useful
> > > information about kernel image: source version, build date, people who built
> > > the kernel image, compiler version. This information is useful for debug and
> > > support. The aim is to get same kind of information but for the DTB.
> > >
> > > > Since you're doing this specifically for use with dtbs built in the
> > > > kernel build, could you just use a:
> > > >     Build-info = /incbin/ "build-info.txt";
> > > > in each of the in-kernel .dts files?
> > >
> > > My first idea was to not modify all existing .dts files. Adding an extra
> > > option in dtc is (for me) the softer way to do it. I mean, compile
> > > information should come through compiler without modify .dts files outside
> > > from dtc. In this way it will be easy to everybody using dtc (inside our
> > > outside Linux tree) to add dtb build info (even if they don't how to write a
> > > dts file).
> >
> > But you're not really having this information coming from the
> > compiler.  Instead you're adding a compiler option that just force
> > includes another file into the generated tree, and it's up to your
> > build scripts to put something useful into that file.
> >
> > I don't really see that as preferable to modifying the .dts files.
> >
> > I also dislike the fact that the option as proposed is much more
> > general than the name suggests, but also very similar too, but much
> > more specific than the existing /incbin/ option.
> >
> > What might be better would be to have a dtc option which force appends
> > an extra .dts to the mail .dts compiled.  You can then put an overlay
> > template in that file, something like:
> >
> > &{/} {
> >         linux,build-info = /incbin/ "build-info.txt;
> > }
> 
> I like this suggestion either as an include another dts file or an
> overlay.

Sorry, to be clear what I'm talking about here is just including
another dts file, and using the compile-type overlay syntax.  This is
not the same as .dtbo style runtime overlays (though the final result
is about the same in this case).

> The latter could be useful as a way to maintain current dtb
> files while splitting the source files into base and overlay dts
> files.
> 
> But no, let's not prepend this with 'linux'. It's not a property
> specific for Linux to consume.

It's not really about who consumes it.  It's about defining a
namespace for the new property to exist in, since it's not part of a
relevant standard (if we wanted to make it such, we should pin down
what goes in there with much more precision).

This is specific to files built in the Linux tree, hence my suggestion
of "linux", whoever ends up consuming them.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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