How to customize u-boot

To customize u-boot you need to modify the sources. First of all, you need to have two different directories, one that contains the exact sources that poky uses to build the system, and another one with your modifications. To explain how to setup those two directories, hereafter will be assumed that you will work inside directory ~/Documents. Open the terminal, than type:

pengwyn@pengwyn-desktop:~/Documents$ mkdir /home/pengwyn/Documents/u-boot-configuration
pengwyn@pengwyn-desktop:~/Documents$ cd /home/pengwyn/Documents/u-boot-configuration
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ cp ../../yocto/poky/meta-silica/recipes-bsp/u-boot/u-boot-pengwyn-2013.01/* .
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ tar -xzf u-boot-pengwyn-2013.01.tar.gz
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ mv u-boot-pengwyn-2013.01 a
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ patch -p1 -d a/ < u-boot-pengwyn-2013.01.patch
patching file arch/arm/cpu/armv7/am33xx/board.c
patching file arch/arm/include/asm/arch-am33xx/cpu.h
patching file arch/arm/include/asm/arch-am33xx/omap_gpmc.h
patching file board/silica/pengwyn/Makefile
patching file board/silica/pengwyn/mux.c
patching file boards.cfg
patching file common/miiphyutil.c
patching file common/spl/spl_nand.c
patching file drivers/mtd/nand/nand_base.c
patching file drivers/mtd/nand/nand_bbt.c
patching file drivers/mtd/nand/nand_ids.c
patching file drivers/mtd/nand/omap_gpmc.c
patching file drivers/net/cpsw.c
patching file drivers/net/phy/Makefile
patching file drivers/net/phy/phy.c
patching file drivers/net/phy/ti.c
patching file include/configs/pengwyn.h
patching file include/linux/mtd/mtd-abi.h
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ cp -r a/ b/

Directory b contains the sources that you can modify. Typically, you will want to modify u-boot settings, in which case you should edit file ~/Documents/u-boot-configuration/ b /include/configs/pengwyn.h with your preferred editor. When you are done with your modifications, type:

pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ diff -Naur a/ b/ > u-boot-pengwyn-2013.01.mine.patch
pengwyn@pengwyn-desktop:~/Documents/u-boot-configuration$ cp u-boot-pengwyn-2013.01.mine.patch /home/pengwyn/yocto/poky/meta-silica/recipes-bsp/u-boot/u-boot-pengwyn-2013.01/

Create a file named u-boot-pengwyn_2013.01.bbappend inside directory /home/pengwyn/yocto/poky/meta-silica/recipes-bsp/u-boot/ and write the following text inside the .bbappend file:

SRC_URI += "file://u-boot-pengwyn-2013.01.mine.patch \
"

You are now ready to build (actually, rebuild) your customized version of u-boot:

pengwyn@pengwyn-desktop:~/yocto/build$ bitbake u-boot-pengwyn -c cleanall

...

pengwyn@pengwyn-desktop:~/yocto/build$ bitbake u-boot-pengwyn

Once the build process finished, the output files (MLO and u-boot-pengwyn.img) will be placed under tmp/deploy/images/ inside your build directory, so, if you are building your system from the default directory, the destination directory will be /home/pengwyn/yocto/build/tmp/deploy/images.