[PATCH] fdt: Allow OF_HAS_PRIOR_STAGE to be disabled in defconfig

[Simon Glass]

Hi Tom,

On Fri, 4 Apr 2025 at 08:02, Tom Rini <trini at konsulko.com> wrote:
>
> On Fri, Apr 04, 2025 at 06:53:49AM +1300, Simon Glass wrote:
>
> > At present it is impossible to change the qemu_arm64 defconfig to
> > obtain a devicetree from the U-Boot build.
> >
> > This is necessary for FIT validation, for example, where the signature
> > node must be compiled into U-Boot.
> >
> > A proposed change to QEMU has been blocked for several years. As a
> > workaround, the only option is to use QEMU's dumpdtb option, merge in
> > the signature node manually and then disable OF_HAS_PRIOR_STAGE
> >
> > Unfortunately the only way to disable OF_HAS_PRIOR_STAGE at present is
> > to hack the Kconfig. So update it to allow use from defconfig. This
> > avoids needing to patch U-Boot to get this working.
> >
> > Signed-off-by: Simon Glass <sjg at chromium.org>
> > Link: https://patchwork.kernel.org/project/qemu-devel/patch/20210926183410.256484-1-sjg@chromium.org/#24481799
>
> How about instead we do something like:
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index b7311d3b754b..44e45a304cd0 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1080,7 +1080,7 @@ config ARCH_QEMU
>         imply DM_RNG
>         imply DM_RTC
>         imply RTC_PL031
> -       imply OF_HAS_PRIOR_STAGE if !TARGET_QEMU_ARM_SBSA
> +       imply OF_HAS_PRIOR_STAGE if !QEMU_MANUAL_DTB
>         imply VIDEO
>         imply VIDEO_BOCHS
>         imply SYS_WHITE_ON_BLACK
> diff --git a/board/emulation/common/Kconfig b/board/emulation/common/Kconfig
> index 4c15c8bcb891..9053f2ff2f55 100644
> --- a/board/emulation/common/Kconfig
> +++ b/board/emulation/common/Kconfig
> @@ -13,3 +13,10 @@ config MTDPARTS_NOR1
>         help
>           This define the partition of nor1 used to build mtparts dynamically
>           for the u-boot env stored on nor1.
> +
> +config QEMU_MANUAL_DTB
> +       bool "Manually provide a device tree to QEMU"
> +       depends on ARCH_QEMU # Expand more if needed
> +       help
> +         For some use cases, such as FIT validation of U-Boot itself we need
> +         to override the device tree that QEMU would normally provide to us.
>
> This way we don't start opening asking OF_HAS_PRIOR_STAGE.

Yes that seems fine, thanks. If it ends up becoming a more general
problem we can worry about it then.

Regards,
Simon