[U-Boot] [U-Boot, v3, 2/3] rockchip: add support for enter to bootrom download mode

[Philipp Tomsich]

> Rockchip bootrom will enter download mode if it returns from
> spl/tpl with a non-zero value and couldn't find a valid image
> in the backup partition.
> This patch provide a method to instruct the system to back to
> bootrom download mode by checking the BROM_DOWNLOAD_FLAG register.
> As the bootrom download function relys on some modules such as
> interrupts, so we need to back to bootrom as early as possbile
> before the tpl/spl code override the interrupt configurations.
> 
> Signed-off-by: Andy Yan <andy.yan at rock-chips.com>
> Reviewed-by: Kever Yang <kever.yang at rock-chips.com>
> ---
> 
> Changes in v3:
> - rebase on Dr. Philipp's series
> 
> Changes in v2:
> - implement the back to bootrom download mode check in c,
>   thanks for Dr. Philipp Tomsich's suggestion.
> 
>  arch/arm/include/asm/arch-rockchip/boot_mode.h |  4 +++
>  arch/arm/mach-rockchip/Kconfig                 |  1 +
>  arch/arm/mach-rockchip/bootrom.c               | 47 ++++++++++++++++++++++++--
>  3 files changed, 50 insertions(+), 2 deletions(-)
> 

Acked-by: Philipp Tomsich <philipp.tomsich at theobroma-systems.com>