[PATCH v6 00/25] fdt: Make OF_BOARD a boolean option

[Tom Rini]

On Thu, Dec 02, 2021 at 05:33:53PM +0100, François Ozog wrote:
> Hi Simon
> 
> Le jeu. 2 déc. 2021 à 17:00, Simon Glass <sjg at chromium.org> a écrit :
> 
> > With Ilias' efforts we have dropped OF_PRIOR_STAGE and OF_HOSTFILE so
> > there are only three ways to obtain a devicetree:
> >
> >    - OF_SEPARATE - the normal way, where the devicetree is built and
> >       appended to U-Boot
> >    - OF_EMBED - for development purposes, the devicetree is embedded in
> >       the ELF file (also used for EFI)
> >    - OF_BOARD - the board figures it out on its own
> >
> > The last one is currently set up so that no devicetree is needed at all
> > in the U-Boot tree. Most boards do provide one, but some don't. Some
> > don't even provide instructions on how to boot on the board.
> >
> > The problems with this approach are documented in another patch in this
> > series: "doc: Add documentation about devicetree usage"
> >
> > In practice, OF_BOARD is not really distinct from OF_SEPARATE. Any board
> > can obtain its devicetree at runtime, even it is has a devicetree built
> > in U-Boot. This is because U-Boot may be a second-stage bootloader and its
> > caller may have a better idea about the hardware available in the machine.
> > This is the case with a few QEMU boards, for example.
> >
> > So it makes no sense to have OF_BOARD as a 'choice'. It should be an
> > option, available with either OF_SEPARATE or OF_EMBED.
> >
> > This series makes this change, adding various missing devicetree files
> > (and placeholders) to make the build work.
> >
> > Note: If board maintainers are able to add their own patch to add the
> > files, some patches in this series can be dropped.
> >
> > It also provides a few qemu clean-ups discovered along the way. The
> > qemu-riscv64_spl problem is fixed.
> >
> > [1]
> > https://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-sjg@chromium.org/
> >
> > Changes in v6:
> > - Fix description of OF_BOARD so it refers just to the current state
> > - Explain that the 'two devicetrees' refers to two *control* devicetrees
> > - Expand the commit message based on comments
> > - Expand the commit message based on comments
> 
> You haven’t addressed any concerns expressed on the mailing list.so I am
> not in favor of this new version either.
> If you make a version without « fake DTs » as you name them, there are good
> advances in the documentation and other areas that would be better in
> mainline….
> If I am the only one thinking this way and the patch can be accepted, I
> would love there is a warning in capital letters at the top of the DTS fake
> files that explains the intent of this fake DT, the possible outcomes of
> not using the one provided by the platform and the right way of dealing
> with DTs for the platform.

This is the part that I too am still unhappy about.  I do not want
reference or fake or whatever device trees in the U-Boot source tree.
We should be able to _remove_ the ones we have, that are not required,
with doc/board/...rst explaining how to get / view one.  Not adding
more.

-- 
Tom
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