[PATCH] ARM: boot: add prepend option for board specific ATAGs

[Sascha Hauer]

On Mon, May 23, 2016 at 10:55:22AM +0200, Alexander Kurz wrote:
> Board specific ATAGs might be passed to vendor provided kernels via the
> ARM_BOARD_APPEND_ATAG option. In this case, the board specific ATAGs will
> be appended to the end of the ATAG list.
> Anyway, some vendor provided kernels might crop the ATAG list at ATAG_MEM,
> also chopping off the board specific ATAGs, see linux squash_mem_tags() as
> reference. The Kindle-3 kernel is one example.
> 
> This conflict might be solved by a) making ATAG_MEM optional which might break
> the existing behavour around squash_mem_tags() or b) by allowing the insertion
> of board specific ATAGs in front of ATAG_MEM which violates the requirement
> from Documentation/arm/Booting to order ATAGs by increasing address.
> 
> Add option to insert board specific ATAGs in front of ATAG_MEM.
> 
> Signed-off-by: Alexander Kurz <akurz at blala.de>
> ---
>  arch/arm/Kconfig        | 10 ++++++++++
>  arch/arm/lib/armlinux.c |  8 +++++++-
>  2 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 1fc887b..71374cc 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -313,6 +313,16 @@ config ARM_BOARD_APPEND_ATAG
>  	  This option is purely to start some vendor provided kernels.
>  	  ** DO NOT USE FOR YOUR OWN DESIGNS! **
>  
> +config ARM_BOARD_PREPEND_ATAG
> +	bool "Prepend the board specific ATAGs"
> +	depends on ARM_BOARD_APPEND_ATAG
> +	help
> +	  Choose this option if your kernel crops the passed ATAG list e.g. at
> +	  ATAG_MEM, also cropping off the board specific ATAGs. This option
> +	  will pass all board specific ATAGs in front of all other ATAGs.
> +	  This option is purely to start some vendor provided kernels.
> +	  ** DO NOT USE FOR YOUR OWN DESIGNS! **
> +
>  endmenu
>  
>  menu "ARM specific settings"
> diff --git a/arch/arm/lib/armlinux.c b/arch/arm/lib/armlinux.c
> index 47b9bd3..962d086 100644
> --- a/arch/arm/lib/armlinux.c
> +++ b/arch/arm/lib/armlinux.c
> @@ -234,6 +234,11 @@ static void setup_tags(unsigned long initrd_address,
>  	const char *commandline = linux_bootargs_get();
>  
>  	setup_start_tag();
> +#if defined(CONFIG_ARM_BOARD_APPEND_ATAG) \
> +	&& defined(CONFIG_ARM_BOARD_PREPEND_ATAG)
> +	if (atag_appender != NULL)
> +		params = atag_appender(params);
> +#endif

You could changle to IS_ENABLED() here to make the code more readable
and to increase compile coverage:

	if (IS_ENABLED(CONFIG_ARM_BOARD_PREPEND_ATAG) && atag_appender)
		...

(Testing for CONFIG_ARM_BOARD_APPEND_ATAG is unnecessary here since
CONFIG_ARM_BOARD_PREPEND_ATAG depends on CONFIG_ARM_BOARD_APPEND_ATAG)

>  	setup_memory_tags();
>  	setup_commandline_tag(commandline, swap);
>  
> @@ -242,7 +247,8 @@ static void setup_tags(unsigned long initrd_address,
>  
>  	setup_revision_tag();
>  	setup_serial_tag();
> -#ifdef CONFIG_ARM_BOARD_APPEND_ATAG
> +#if defined(CONFIG_ARM_BOARD_APPEND_ATAG) \
> +	&& !defined(CONFIG_ARM_BOARD_PREPEND_ATAG)

Same here, IS_ENABLED() would be nicer.

Sascha

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