linux-kernel - Re: [RFC PATCH v2 0/4] Add device tree build information

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Date:   Fri, 21 Feb 2020 11:47:44 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Alexandre Torgue <alexandre.torgue@...com>, robh+dt@...nel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        david@...son.dropbear.id.au, sjg@...omium.org
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org, devicetree-compiler@...r.kernel.org,
        Ian Lepore <ian@...ebsd.org>
Subject: Re: [RFC PATCH v2 0/4] Add device tree build information

On 2/21/20 10:14 AM, Alexandre Torgue wrote:
> (with title it's better ;)
> 
> Hi,
> 
> The goal of this series is to add device tree build information in dtb.
> This information can be dtb build date, where devicetree files come from,
> who built the dtb ... Actually, same kind of information that you can find
> in the Linux banner which is printout during kernel boot. Having the same
> kind of information for device tree is useful for debugging and maintenance.
> 
> A file (dtb-build.txt) containing a string with build information (e.g.,
>>>From Linux 5.5.0-rc1 by alex the Mon Jan 13 18:25:38 CET 2020) is generated by
> "gen_dtb_build_info.sh" script. 
> 
> This file has to be included manually in each dts file that would like to use 
> this build information.

In the RFC series, you said:

  "I gonna prepare a V2 with David proposition (to use overlay format) by
   keeping in mind not to modify existing dts(i) files."

   https://lore.kernel.org/linux-devicetree/9d83a36c-78c5-3452-bb48-209d68c46038@st.com/

But here in v2 instead requires including dtb-build.txt.

This would require modifying every single main .dts file to get the build info.
I would prefer the method that Ian and David came up with (sorry, no lore link,
it did not go to lkml).  Extract from David's email:

   Date:   Tue, 21 Jan 2020 13:05:25 +1100
   From:   David Gibson <david@...son.dropbear.id.au>
   Subject: Re: [RFC PATCH 1/3] dtc: Add dtb build information option

   > Given that dts files are run through the C preprocessor before being
   > fed to dtc, the build script could use the '-include' flag to force-
   > include a fragment containing generated build info without any need to
   > modify existing dts files.

   Uh... maybe.  -include will essentially prepend the forced file, which
   is a bit awkward for our purposes.  It means that the prepended file
   would need the /dts-v1/ tag, and we couldn't have it in the main files
   which would be a bit confusing.  I think it would also cause problems
   with any /memreserve/ tags and means that the main tree could in
   theory overwrite the build information which we don't necessarily
   want.

   I guess we could build things the other way around: have the main .dts
   file specified with -include and have the dts on the dtc commandline
   be a fixed one with the build information.  It'd be a little weird,
   though.

-Frank

> 
> of/fdt.c is modified to printout "build-info" property during Kernel boot and 
> scripts/Makefile.lib is modified to call "gen_dtb_build_info.sh" script.
> 
> Patch 1 & 2 script and of/fdt.c updates
> Patch 3 is an example of use in stm32mp157c-dk2.dts file.
> Patch 4 is a tentative to make it automatic (not yet 100% functional).
> 
> regards
> Alex
> 
> Changes since v1;
>  - Remove modification in dtc (no more -B option)
>  - Generate a file containing build info which is directly included in dts
>    file.
> 
> 
> Regards
> Alex
> 
> Alexandre Torgue (4):
>   scripts: Add script to generate dtb build information
>   of: fdt: print dtb build information
>   ARM: dts: stm32: Add dtb build information entry for stm32mp157c-dk2
>   script: make automatic dtb build info generation
> 
>  arch/arm/boot/dts/stm32mp157c-dk2.dts |  1 +
>  drivers/of/fdt.c                      |  9 +++++++++
>  scripts/Makefile.lib                  |  3 +++
>  scripts/gen_dtb_build_info.sh         | 12 ++++++++++++
>  4 files changed, 25 insertions(+)
>  create mode 100755 scripts/gen_dtb_build_info.sh
>