Re: [RFC][PATCH] kbuild: Generate symbols for DTO application in DTBs

[Masahiro Yamada <masahiroy@kernel.org>]

Hi Marek.
(+CC Rob, DT ML)

On Thu, Apr 7, 2022 at 8:05 PM Marek Vasut <marex@denx.de> wrote:
>
> Emit symbols section in DTBs to permit symbol resolution when applying DTOs.

I CCed DT folks, but if I remember correctly, adding -@ globally
was NACKed because it would increase blob size for platforms that
do not need overlay.


> Signed-off-by: Marek Vasut <marex@denx.de>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> ---
> NOTE: I am sending this as RFC, because I suspect there is a better way how
>       to pass extra flags to DTC during kernel build ?
>       Maybe from shell environment somehow ?


For local use, yes, you can add -@ from the command line.

Try this:

    DTC_FLAGS=-@  make ARCH=arm64 dtbs


This is undocumented tip, but it seems to work
for the current code.



>       Or maybe b7e70391a5451 ("arm64: tegra: Enable device-tree overlay support")
>       is the way to go about this ?


Since commit 15d16d6dadf6947ac7f9a686c615995c5a426ce2,
adding -@ is automatic for platforms that support overlay.


If  <platform>-dtbs exists, -@ is automatically added.

See arch/arm64/boot/dts/xilinx/Makefile
as an example code.





> ---
>  arch/arm/boot/dts/Makefile   | 3 +++
>  arch/arm64/boot/dts/Makefile | 3 +++
>  2 files changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/Makefile b/arch/arm/boot/dts/Makefile
> index 252353fb4e3b3..2d50302d077dd 100644
> --- a/arch/arm/boot/dts/Makefile
> +++ b/arch/arm/boot/dts/Makefile
> @@ -1,4 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
> +
> +DTC_FLAGS += -@
> +
>  dtb-$(CONFIG_ARCH_ALPINE) += \
>         alpine-db.dtb
>  dtb-$(CONFIG_MACH_ARTPEC6) += \
> diff --git a/arch/arm64/boot/dts/Makefile b/arch/arm64/boot/dts/Makefile
> index 1ba04e31a4387..f7b3c86517a0e 100644
> --- a/arch/arm64/boot/dts/Makefile
> +++ b/arch/arm64/boot/dts/Makefile
> @@ -1,4 +1,7 @@
>  # SPDX-License-Identifier: GPL-2.0
> +
> +DTC_FLAGS += -@
> +
>  subdir-y += actions
>  subdir-y += allwinner
>  subdir-y += altera
> --
> 2.35.1
>


-- 
Best Regards
Masahiro Yamada