[U-Boot] [RFC PATCH 1/2] kbuild: add a makefile macro useful with per-image config options

[Tom Rini]

On Thu, Jul 23, 2015 at 08:31:55PM +0900, Masahiro Yamada wrote:

> Commit e02ee2548afe ("kconfig: switch to single .config
> configuration") made the configuration itself pretty simple,
> instead, we lost the way to systematically enable/disable config
> options for each image independently.
> 
> Our current strategy is, put entries into Makefile.spl for options
> we need separate enabling, or once enable the options globally in
> Kconfig and then undef them in Makefile.uncmd_spl if we do not want
> to compile the features for SPL at all.  Things are getting really
> messy.  Besides, "ifdef CONFIG_SPL_BUILD" are sprinkled everywhere
> in makefiles.
> 
> This commit adds a macro to help describe makefile simpler, allowing
> separate switch for U-boot main and SPL.
> 
> This macro takes a config option without the prefix CONFIG_.
> $(call CONFIG,FOO) evaluates to
>   $(CONFIG_FOO) if CONFIG_SPL_BUILD is undefined (U-boot build),
>   $(CONFIG_SPL_FOO) if CONFIG_SPL_BUILD is defined (SPL_BUILD).
> 
> That is,
> 
>   $(call CONFIG,FOO) += foo.o
> 
> is a shorthand for
> 
>   ifdef CONFIG_SPL_BUILD
>   obj-$(CONFIG_SPL_FOO) += foo.o
>   else
>   obj-$(CONFIG_FOO) += foo.o
>   endif
> 
> If CONFIG_SPL_FOO does not exist in Kconfig, it is equivalent to
> 
>   ifndef CONFIG_SPL_BUILD
>   obj-$(CONFIG_SPL_FOO) += foo.o
>   endif
> 
> This is the pattern we often see in our current makefiles.
> 
> To take advantage of this macro, we should prefix SPL_ for the SPL
> version of the option that we need independent control between
> U-boot and SPL.  With this naming scheme, we only have to add a
> single line in a Makefile for each config option.
> 
> It means we want to rename existing config options as follows
> in the long run:
> 
>   CONFIG_SPL_SERIAL_SUPPORT     -> CONFIG_SPL_SERIAL
>   CONFIG_SPL_I2C_SUPPORT        -> CONFIG_SPL_I2C
>   CONFIG_SPL_GPIO_SUPPORT       -> CONFIG_SPL_GPIO
>   CONFIG_SPL_SPI_SUPPORT        -> CONFIG_SPL_SPI
>   CONFIG_SPL_DISABLE_OF_CONTROL -> CONFIG_SPL_OF_CONTROL
>                                       (inverting the logic)
> 
> Then drivers/Makefile would be re-worked as follows:
> 
>   obj-$(call CONFIG,SERIAL)  += serial/
>   obj-$(call CONFIG,I2C)     += i2c/
>   obj-$(call CONFIG,GPIO)    += gpio/
>   obj-$(call CONFIG,SPI)     += spi/
>      ...
> 
> Eventually, SPL-specialized entries in Makefile.spl would go away.
> 
> Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>

Reviewed-by: Tom Rini <trini at konsulko.com>

-- 
Tom
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