U-Boot

In your linux SDK root directory. enter to U-Boot directory. 

cd u-boot

For RK3399 sapphire-excavator board, VS-RK3399 board, Rock960 board. Use below command to build the U-Boot: 

./make.sh evb-rk3399

For firefly-rk3399 board. Use below command to build the U-Boot: 

./make.sh firefly-rk3399

For firefly-rk3288 board. Use below command to build the U-Boot: 

./make.sh firefly-rk3288

For rk3288-evb-act8846 board. Use below command to build the U-Boot: 

./make.sh evb-rk3288

For rk3288-evb-rk808 board. Use below command to build the U-Boot: 

./make.sh fennec-rk3288

For rk3288 tinker board. Use below command to build the U-Boot: 

./make.sh tinker-rk3288

For phytec-rk3288 board. Use below command to build the U-Boot: 

./make.sh phycore-rk3288

For rk3288 miqi board. Use below command to build the U-Boot: 

./make.sh miqi-rk3288

It will generate 3 binary image: rk3xxx_loader_vx.xx.xxx.bin, trust.img, uboot.img. 

rk3xxx_loader_vx.xx.xxx.bin: Rockchip miniloader. rk3xxx is the part number of the chip. vx.xx.xxx is the version number. Please flash this binary to miniloader partition. 

trust.img: ARM Trusted Firmware, Please flash this binary to trust partition

uboot.img: The U-Boot image, Please flash this binary to uboot partition

u-boot/
├── rk3399_loader_v1.09.112.bin
├── trust.img
└── uboot.img

Rockchip now only offically support miniloader+U-Boot boot to simplify the customer product design.  You can refer to boot option page for more boot path. But do remember that you should do it all by your own. Rockchip won't provide technical support for these boot option.