[PATCH v5 1/7] qemu-arm: merge built-in DT

[Simon Glass]

Hi Ludwig,

On 2026-05-28T11:47:57, Ludwig Nussel <ludwig.nussel at siemens.com> wrote:
> qemu-arm: merge built-in DT
>
> The keys trusted for FIT signature verification are supposed to be
> embedded in the device tree built into u-boot. When running in Qemu it's
> convenient to use the device tree provided by the VM which doesn't know
> about signatures though. So merge both device trees at startup.
>
> Signed-off-by: Ludwig Nussel <ludwig.nussel at siemens.com>
>
> board/emulation/qemu-arm/qemu-arm.c | 47 +++++++++++++++++++++++++++++++++++--
>  configs/qemu_arm64_defconfig        |  1 +
>  2 files changed, 46 insertions(+), 2 deletions(-)

Reviewed-by: Simon Glass <sjg at chromium.org>

> diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
> @@ -144,10 +144,53 @@ int dram_init_banksize(void)
> +/* QEMU loads a generated DTB for us at the start of RAM.
> + * When using signatures we may have a built-in FDT that contains
> + * our known public keys nevertheless. So merge the built in FDT
> + * into QEMU's. We cannot merge the other way around (eg in
> + * fdtdec_board_setup()) or board_fix_fdt() at this stage as U-Boot
> + * might be started from a ROM location. At the same time U-Boot
> + * needs QEMU's FDT to initialize serial devices even before
> + * relocation.
> + */

Please use kernel multi-line comment style: '/*' on its own line,
prose starting on the next. Also 'eg' should be 'e.g.' and 'built in'
as an adjective is 'built-in'.

> diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
> @@ -144,10 +144,53 @@ int dram_init_banksize(void)
> +     ret = fdt_increase_size(qemu_fdt, 1024 + fdt_totalsize(*fdtp));
> +     if (ret) {
> +             log_err("Failed to resize FDT overlay: %s", fdt_strerror(ret));
> +             goto out;
> +     }

Missing trailing '\n' - the next log_err() has one. Also, qemu_fdt is
the base we're growing to receive the overlay, not the overlay itself;
"Failed to grow QEMU FDT" would be clearer.

> diff --git a/board/emulation/qemu-arm/qemu-arm.c b/board/emulation/qemu-arm/qemu-arm.c
> @@ -144,10 +144,53 @@ int dram_init_banksize(void)
> +     ret = fdt_overlay_apply_node(qemu_fdt, 0, (void *)*fdtp, 0);
> +     if (ret) {
> +             log_err("Failed to apply FDT overlay: %s\n", fdt_strerror(ret));
> +             goto out;
> +     }
> +
> +out:
> +     *fdtp = qemu_fdt;
> +
>       return 0;
> }

On failure we log and return 0 with a partially-modified qemu_fdt.
Please propagate the error - otherwise a board with
FIT_SIGNATURE_REQUIRED (added later in the series) silently boots
without keys merged and presumably fails much later. The (void *) cast
on *fdtp is also redundant, isn't it?

> diff --git a/configs/qemu_arm64_defconfig b/configs/qemu_arm64_defconfig
> @@ -38,6 +38,7 @@ CONFIG_CMD_EFIDEBUG=y
> +# CONFIG_OF_OMIT_DTB is not set

The commit message doesn't mention this. Please add a sentence
explaining that OF_OMIT_DTB must be off so the built-in DT is present
to merge from, and note whether qemu_arm_defconfig needs the same
treatment.

Regards,
Simon