[PATCH v2] emulation: fdt: Allow using U-Boot's device tree with QEMU

[Tom Rini]

On Sun, Apr 06, 2025 at 07:07:04AM +1200, 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 to allow device tree additions has been
> blocked for several years. The only known workaround is to use QEMU's
> dumpdtb option, merge in the signature node manually, disable
> OF_HAS_PRIOR_STAGE and then start QEMU with special arguments. This is
> complicated enough that it is documented in U-Boot[1].

This paragraph and then

[snip]
> +	  Note: this work-around is necessary since Linaro has blocked
> +	  addition of a feature to support additions to the QEMU devicetree:

This part of the help are overly antagonistic.

[snip]
> diff --git a/dts/Kconfig b/dts/Kconfig
> index 2e88d210bb8..53f7e246a80 100644
> --- a/dts/Kconfig
> +++ b/dts/Kconfig
> @@ -205,8 +205,13 @@ config OF_HAS_PRIOR_STAGE
>  	  development purposes, but it is not recommended, and likely will not
>  	  even work, for production systems.
>  
> -	  Note: This option must be set in Kconfig and cannot be enabled or
> -	  disabled in the board's defconfig file.
> +	  Note: This option can be disabled for QEMU usiing QEMU_MANUAL_DTB thus
> +	  allowing QEMU to support FIT validation, where the devicetree must
> +	  include a public key.
> +
> +	  See also this for context:
> +
> +	  https://patchwork.kernel.org/project/qemu-devel/patch/20210926183410.256484-1-sjg@chromium.org/#24481799

And we don't need more wording here. The QEMU_MANUAL_DTB option itself
is enough.

-- 
Tom
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