View source for How to customize the Linux kernel

===Adding kernel configuration modifications===
* Identify all new configs you set or unset with: {{PC$}} bitbake <name of kernel recipe> -c menuconfig
* Put them inside a new fragment file and copy the fragment here:
 {{PC$}} cp <custom-fragment>.config  ../meta-my-custo-layer/recipes-kernel/linux/<name of kernel recipe>/<kernel version>/
* Update accordingly <name of kernel recipe>.bbappend:
 KERNEL_CONFIG_FRAGMENTS_append += "${WORKDIR}/fragments/<kernel version>/<custom-fragment>.config"
 SRC_URI_append = " file://<kernel version>/<custom-fragment>.config;subdir=fragments "

For the use case described in the [[How to cross-compile with the Distribution Package#modifying_kernel_configuration]] example, you should:
* Create fragment-cma-size.config with the following line:
CONFIG_CMA_SIZE_MBYTES=256
* Copy fragment-cma-size.config to ../meta-my-custo-layer/recipes-kernel/linux/linux-stm32mp/4.14/
* Update ../meta-my-custo-layer/recipes-kernel/linux/linux-stm32mp.bbappend accordingly by adding these lines:
 KERNEL_CONFIG_FRAGMENTS_append += "${WORKDIR}/fragments/4.14/fragment-cma-size.config"
 SRC_URI_append = " file://4.14/fragment-cma-size.config;subdir=fragments "