linux-kernel - Re: [PATCH v2 2/2] mips: generic: allow not building DTB in

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Date:   Tue, 26 Jun 2018 16:07:43 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     James Hogan <jhogan@...nel.org>, Ralf Baechle <ralf@...ux-mips.org>
Cc:     Paul Burton <paul.burton@...s.com>, linux-mips@...ux-mips.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mips: generic: allow not building DTB in

On 26/06/2018 13:57:12+0200, Alexandre Belloni wrote:
> Allow not building any DTB in the generic kernel so it gets smaller. This
> is necessary for ocelot because it can be built as a legacy platform that
> needs a built-in DTB and it can also handle a separate DTB once it is
> updated with a more modern bootloader. In the latter case, it is preferable
> to not include any DTB in the kernel image so it is smaller.
> 
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...tlin.com>
> ---
> Changes in v2:
>  - rebased on v4.18-rc1
> 

Note that while the first patch can probably be applied as-is (it only
affects Ocelot). this one still needs to be refined. It seems to be
causing build issues with some defconfig.

>  arch/mips/Kconfig               | 1 -
>  arch/mips/Makefile              | 2 +-
>  arch/mips/generic/Kconfig       | 1 +
>  arch/mips/generic/vmlinux.its.S | 2 ++
>  4 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 3f9deec70b92..2cc43f51fa6f 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -85,7 +85,6 @@ choice
>  config MIPS_GENERIC
>  	bool "Generic board-agnostic MIPS kernel"
>  	select BOOT_RAW
> -	select BUILTIN_DTB
>  	select CEVT_R4K
>  	select CLKSRC_MIPS_GIC
>  	select COMMON_CLK
> diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> index e2122cca4ae2..5c5d491d736e 100644
> --- a/arch/mips/Makefile
> +++ b/arch/mips/Makefile
> @@ -401,7 +401,7 @@ endif
>  CLEAN_FILES += vmlinux.32 vmlinux.64
>  
>  # device-trees
> -core-$(CONFIG_BUILTIN_DTB) += arch/mips/boot/dts/
> +core-y += arch/mips/boot/dts/
>  
>  %.dtb %.dtb.S %.dtb.o: | scripts
>  	$(Q)$(MAKE) $(build)=arch/mips/boot/dts arch/mips/boot/dts/$@
> diff --git a/arch/mips/generic/Kconfig b/arch/mips/generic/Kconfig
> index 08e33c6b2539..13692b84928e 100644
> --- a/arch/mips/generic/Kconfig
> +++ b/arch/mips/generic/Kconfig
> @@ -3,6 +3,7 @@ if MIPS_GENERIC
>  
>  config LEGACY_BOARDS
>  	bool
> +	select BUILTIN_DTB
>  	help
>  	  Select this from your board if the board must use a legacy, non-UHI,
>  	  boot protocol. This will cause the kernel to scan through the list of
> diff --git a/arch/mips/generic/vmlinux.its.S b/arch/mips/generic/vmlinux.its.S
> index 1a08438fd893..9c954f2ae561 100644
> --- a/arch/mips/generic/vmlinux.its.S
> +++ b/arch/mips/generic/vmlinux.its.S
> @@ -21,6 +21,7 @@
>  		};
>  	};
>  
> +#if IS_ENABLED(CONFIG_BUILTIN_DTB)

Thinking more about that, the conf@...ault configuration should probably
not be removed if the platform is not using DT at all. Are there still
MIPS platforms without DT support?

>  	configurations {
>  		default = "conf@...ault";
>  
> @@ -29,4 +30,5 @@
>  			kernel = "kernel@0";
>  		};
>  	};
> +#endif
>  };
> -- 
> 2.18.0
> 

-- 
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com