After several recompilations I finally got what I wanted on my Chromebook. Clean and easy way of booting own kernel.
Now situation is clean and easy:
- power on Chromebook
- ChromeOS U-Boot from SPI flash starts
- white screen of warning appears
- Ctrl-d to skip it
- U-Boot starts from mmcblk0p1
- U-Boot reads boot.txt from mmcblk0p2 (ext2 /boot/ partition)
- U-Boot reads uImage kernel and exynos5250-snow.dtb file from mmcblk0p2
- Kernel boots directly to Fedora F19 stored on mmcblk0p3
This way I can quickly test mainline kernels (but this may require U-Boot change for simplefb support), manipulate 3.-chromeos ones etc.
Next step would be replace bootloader stored in SPI flash but this voids warranty so let it wait a bit.