Message-ID: <20200117090937.GU54439@umbus>
Date:   Fri, 17 Jan 2020 19:09:37 +1000
From:   David Gibson <david@...son.dropbear.id.au>
To:     Alexandre Torgue <alexandre.torgue@...com>
Cc:     robh+dt@...nel.org, Frank Rowand <frowand.list@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>, sjg@...omium.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org, devicetree-compiler@...r.kernel.org,
        Steve McIntyre <steve.mcintyre@...aro.org>
Subject: Re: [RFC PATCH 1/3] dtc: Add dtb build information option

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;
}

-- 
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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