[U-Boot] [U-Boot, 12/13] armv7: support rk3066 early back to bootrom in start.S

[Philipp Tomsich]

> Rockchip bootrom first reads 1KB data from nand at offset 0x10080C00 and
> executes it. Then waits for back to bootrom and loads another 32KB to sram
> which also executes. Sdram initialisation code needs to be in one of these two
> steps. Then bootloader loads another ~200KB of data at offset 0x60000000
> and jumps to it.
> 
> 32KB of data is a little low for tpl + spl part and ~200KB data is to low for
> u-boot part(for example to boot from mmc you need to disable usb support.
> 
> My solution to size problem is to move sdram initialisation code to tpl stage,
> move spl part to third stage(reading 200KB data) and add support for loading
> u-boot by spl from ext2/4, fat partitions.
> 
> But moving sdram initialisation code to tpl increases size of tpl above 1KB
> (first boot stage). Solution to this is to add code which will be below 1KB
> offset in tpl binary and do back to bootrom at very beginning of the tpl
> execution.
> 
> Adding this few lines of code here meets these conditions.
> 
> Signed-off-by: Paweł Jarosz <paweljarosz3691 at gmail.com>
> ---
>  arch/arm/cpu/armv7/start.S | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 

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