[PATCH 00/16] fdt: Make OF_BOARD a boolean option

Bin Meng bmeng.cn at gmail.com
Wed Oct 13 03:29:14 CEST 2021

Hi Simon,

On Wed, Oct 13, 2021 at 9:01 AM Simon Glass <sjg at chromium.org> wrote:
> 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 at [1].
> 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.

Adding device trees that are never used sounds like a hack to me.

For QEMU, device tree is dynamically generated on the fly based on
command line parameters, and the device tree you put in this series
has various hardcoded <phandle> values which normally do not show up
in hand-written dts files.

I am not sure I understand the whole point of this.

> It also provides a few qemu clean-ups discovered along the way.
> This series is based on Ilias' two series for OF_HOSTFILE and
> OF_PRIOR_STAGE removal.
> It is available at u-boot-dm/ofb-working
> [1] https://patchwork.ozlabs.org/project/uboot/patch/20210919215111.3830278-3-sjg@chromium.org/


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