Re: [RFC PATCH 1/3] dtc: Add dtb build information option

[Alexandre Torgue]

David, Rob,

On 1/17/20 3:43 PM, Rob Herring wrote:
> On Fri, Jan 17, 2020 at 6:26 AM David Gibson
> <david@xxxxxxxxxxxxxxxxxxxxx> 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@xxxxxx>
> > > >
> > > > 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.

ok

> > > > 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 agree. I took example on kernel version info. It doesn't come from gcc 
but from auto-generated file. I thought it was the easier way to 
process. But I understand your concerns. As it is not generated by dtc 
itself, dtc should not be modified.

> > 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. The latter could be useful as a way to maintain current dtb
> files while splitting the source files into base and overlay dts
> files.

First suggestion will imply to modify an huge part of dts file (not a 
big modification but a lot :)).
Second one (dtbo) sounds good. In this case this dtso will be created 
from build-info.txt and applied when dtb is built. So no impacts on 
current dts file. I'm right ?

Alex

> But no, let's not prepend this with 'linux'. It's not a property
> specific for Linux to consume.
>
> Rob