[RFC PATCH 1/1] riscv: dts: Allow BUILTIN_DTB for all socs

[Yangyu Chen]

On Wed, 2024-02-21 at 03:03 +0800, Yangyu Chen wrote:
> The BUILTIN_DTB kernel feature on RISC-V only works on K210 SoC only.
> This
> patch moved this configuration to entire riscv.
> 
> Signed-off-by: Yangyu Chen <cyy at cyyself.name>
> ---
>  arch/riscv/Kconfig                  | 16 ++++++++++++++-
>  arch/riscv/Kconfig.socs             | 32 ---------------------------
> --
>  arch/riscv/boot/dts/Makefile        |  2 +-
>  arch/riscv/boot/dts/canaan/Makefile |  2 --
>  4 files changed, 16 insertions(+), 36 deletions(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index b49016bb5077..23d501561e64 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -996,7 +996,21 @@ config RISCV_ISA_FALLBACK
>  config BUILTIN_DTB
>  	bool "Built-in device tree"
>  	depends on OF && NONPORTABLE
> -	default y if XIP_KERNEL
> +	default y if XIP_KERNEL || SOC_CANAAN
> +	help
> +	  Build a device tree into the Linux image.
> +	  This option should be selected if no bootloader is being
> used.
> +	  If unsure, say Y.
> +
> +
> +config BUILTIN_DTB_SOURCE
> +	string "Built-in device tree source"
> +	depends on BUILTIN_DTB
> +	default "canaan/k210_generic" if SOC_CANAAN
> +	help
> +	  DTS file path (without suffix, relative to
> arch/riscv/boot/dts)
> +	  for the DTS file that will be used to produce the DTB
> linked into the
> +	  kernel.
>  
>  endmenu # "Boot options"
>  
> diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
> index e08e91c49abe..623de5f8a208 100644
> --- a/arch/riscv/Kconfig.socs
> +++ b/arch/riscv/Kconfig.socs
> @@ -84,36 +84,4 @@ config SOC_CANAAN
>  	help
>  	  This enables support for Canaan Kendryte K210 SoC platform
> hardware.
>  
> -if ARCH_CANAAN
> -
> -config ARCH_CANAAN_K210_DTB_BUILTIN
> -	def_bool SOC_CANAAN_K210_DTB_BUILTIN
> -
> -config SOC_CANAAN_K210_DTB_BUILTIN
> -	bool "Builtin device tree for the Canaan Kendryte K210"
> -	depends on ARCH_CANAAN
> -	default y
> -	select OF
> -	select BUILTIN_DTB
> -	help
> -	  Build a device tree for the Kendryte K210 into the Linux
> image.
> -	  This option should be selected if no bootloader is being
> used.
> -	  If unsure, say Y.
> -
> -config ARCH_CANAAN_K210_DTB_SOURCE
> -	string
> -	default SOC_CANAAN_K210_DTB_SOURCE
> -
> -config SOC_CANAAN_K210_DTB_SOURCE
> -	string "Source file for the Canaan Kendryte K210 builtin
> DTB"
> -	depends on ARCH_CANAAN
> -	depends on ARCH_CANAAN_K210_DTB_BUILTIN
> -	default "k210_generic"
> -	help
> -	  Base name (without suffix, relative to
> arch/riscv/boot/dts/canaan)
> -	  for the DTS file that will be used to produce the DTB
> linked into the
> -	  kernel.
> -
> -endif # ARCH_CANAAN
> -
>  endmenu # "SoC selection"
> diff --git a/arch/riscv/boot/dts/Makefile
> b/arch/riscv/boot/dts/Makefile
> index 72030fd727af..318239d9423b 100644
> --- a/arch/riscv/boot/dts/Makefile
> +++ b/arch/riscv/boot/dts/Makefile
> @@ -8,4 +8,4 @@ subdir-y += sophgo
>  subdir-y += starfive
>  subdir-y += thead
>  
> -obj-$(CONFIG_BUILTIN_DTB) := $(addsuffix /, $(subdir-y))
> +obj-$(CONFIG_BUILTIN_DTB) := $(addsuffix .dtb.o,
> $(CONFIG_BUILTIN_DTB_SOURCE))
> \ No newline at end of file
> diff --git a/arch/riscv/boot/dts/canaan/Makefile
> b/arch/riscv/boot/dts/canaan/Makefile
> index 520623264c87..987d1f0c41f0 100644
> --- a/arch/riscv/boot/dts/canaan/Makefile
> +++ b/arch/riscv/boot/dts/canaan/Makefile
> @@ -5,5 +5,3 @@ dtb-$(CONFIG_ARCH_CANAAN) += sipeed_maix_bit.dtb
>  dtb-$(CONFIG_ARCH_CANAAN) += sipeed_maix_dock.dtb
>  dtb-$(CONFIG_ARCH_CANAAN) += sipeed_maix_go.dtb
>  dtb-$(CONFIG_ARCH_CANAAN) += sipeed_maixduino.dtb
> -
> -obj-$(CONFIG_ARCH_CANAAN_K210_DTB_BUILTIN) += $(addsuffix .dtb.o,
> $(CONFIG_ARCH_CANAAN_K210_DTB_SOURCE))

After carefully reviewing the code from the kernel I found that
`arch/riscv/boot/dts/sifive(microchip)/Makefile` will also build the
dtb object file and finally link to the kernel. This results in
multiple dtb inside the kernel but the kernel always takes the first to
use as someone mentioned before [1]. So only applying this patch to the
mainline kernel does not work for choosing one dtb. I should also
revert the modification on commit 0ddd7eaffa64 ("riscv: Fix BUILTIN_DTB
for sifive and microchip soc") to prevent building these files and let
them be managed by `arch/riscv/boot/dts/Makefile`.

I'm also waiting for other review comments on this idea before
submitting patch v2.

[1]
https://lore.kernel.org/linux-riscv/CAK7LNATt_56mO2Le4v4EnPnAfd3gC8S_Sm5-GCsfa=qXy=8Lrg@mail.gmail.com/