Difference between revisions of "How to customize the Linux kernel"

[quality revision] [quality revision]
m (Adding kernel driver or device tree modifications)
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Applicable for STM32MP13x lines, STM32MP15x lines

1 Purpose of article[edit]

This article gives the main steps needed to add kernel customization within the Yocto build process (with a Distribution Package).

2 Pre-requesites[edit]

You are already familiar with the Yocto build process and OpenSTLinux distribution.

You have already created a customer layer (How to create a new open embedded layer) to update, for your own needs, the OpenSTLinux distribution.

We describe here what you must do once you have:

so that these modifications are taken into account in your build process.

3 Adding kernel customization (including Linux kernel device tree, configuration, driver modification)[edit]

  • First, create (in your custom layer) a <name of kernel recipe>.bbappend file
 touch ../meta-my-custo-layer/recipes-kernel/linux/<name of kernel recipe>.bbappend

3.1 Adding kernel configuration modifications[edit]

  • Identify all new configs you set or unset with: bitbake <name of kernel recipe> -c menuconfig
  • Put them inside a new fragment file and copy the fragment here:
 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/<kernel version>
  • Update ../meta-my-custo-layer/recipes-kernel/linux/linux-stm32mp.bbappend accordingly by adding these lines:
KERNEL_CONFIG_FRAGMENTS_append += "${WORKDIR}/fragments/${LINUX_VERSION}/fragment-cma-size.config"
SRC_URI_append = " file://${LINUX_VERSION}/fragment-cma-size.config;subdir=fragments "

3.2 Adding kernel driver or device tree modifications[edit]

The example given below is associated with the STM32MP15 Evaluation board, but the method is independent of the board.

Once you have made the changes for the device tree in <build dir>/workspace/sources/<name of kernel recipe>/arch/arm/boot/dts/stm32mp157c-ed1.dts AND, for built-in device driver in <build dir>/workspace/sources/<name of kernel recipe>/drivers/gpu/drm/stm/drv.c, you must:

  • Create the corresponding patch files:
 cd <build dir>/workspace/sources/<name of kernel recipe>/
 git format-patch -2
  • Copy these patch files into the custom layer
 cp *.patch ../meta-my-custo-layer/recipes-kernel/linux/<name of kernel recipe>/<kernel version>/<kernel version>.<revision>/
Warning white.png Warning
Patches are linked to a kernel version, which means that these patches are rebuilt if the kernel version changes, and copied to the according kernel version sub-folder
  • Update <name of kernel recipe>.bbappend accordingly:
SRC_URI_append = " \
   file://${LINUX_VERSION}/${LINUX_VERSION}.${LINUX_SUBVERSION}/0001-DT-leds-change.patch \
   file://${LINUX_VERSION}/${LINUX_VERSION}.${LINUX_SUBVERSION}/0002-Driver-change.patch \
   "


==<noinclude>{{ApplicableFor
|MPUs list=STM32MP13x, STM32MP15x
|MPUs checklist=STM32MP13x,STM32MP15x
}}</noinclude>

==Purpose of article==
This article gives the main steps needed to add kernel customization within the Yocto build process (with a Distribution Package).

==Pre-requesites==
You are already familiar with the Yocto build process and OpenSTLinux distribution.

You have already created a customer layer ([[How to create a new open embedded layer]]) to update, for your own needs, the OpenSTLinux distribution.<br>


We describe here what you must do once you have:
* [[How to cross-compile with the Distribution Package#modifying_kernel_configuration|modified the kernel configuration]]
* [[How to cross-compile with the Distribution Package#Modifying_the_Linux_kernel_device_tree|modified the Linux kernel device tree]]
* [[How to cross-compile with the Distribution Package#Modifying_a_built-in_Linux_kernel_device_driver|modified a built-in device driver]]
so that these modifications are taken into account in your build process.

==Adding kernel customization (including Linux kernel device tree, configuration, driver modification)==

* First, create (in your custom layer) a <name of kernel recipe>.bbappend file
 {{PC$}} touch ../meta-my-custo-layer/recipes-kernel/linux/<name of kernel recipe>.bbappend

===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/<kernel version>

* Update ../meta-my-custo-layer/recipes-kernel/linux/linux-stm32mp.bbappend accordingly by adding these lines:
 KERNEL_CONFIG_FRAGMENTS_append += "${WORKDIR}/fragments/${LINUX_VERSION}/fragment-cma-size.config"
 SRC_URI_append = " file://${LINUX_VERSION}/fragment-cma-size.config;subdir=fragments "

===Adding kernel driver or device tree modifications===
The example given below is associated with the STM32MP15 Evaluation board, but the method is independent of the board.

Once you have made the changes for the device tree in <build dir>/workspace/sources/<name of kernel recipe>/arch/arm/boot/dts/stm32mp157c-ed1.dts '''AND''', for built-in device driver in <build dir>/workspace/sources/<name of kernel recipe>/drivers/gpu/drm/stm/drv.c, you must:

* Create the corresponding patch files:
 {{PC$}} cd <build dir>/workspace/sources/<name of kernel recipe>/
 {{PC$}} git format-patch -2
* Copy these patch files into the custom layer
 {{PC$}} cp *.patch ../meta-my-custo-layer/recipes-kernel/linux/<name of kernel recipe>/<kernel version>/<kernel version>.<revision>/
{{Warning|Patches are linked to a kernel version, which means that these patches are rebuilt if the kernel version changes, and copied to the according kernel version sub-folder}}
* Update <name of kernel recipe>.bbappend accordingly:
 SRC_URI_append = " \
    file://${LINUX_VERSION}/${LINUX_VERSION}.${LINUX_SUBVERSION}/0001-DT-leds-change.patch \
    file://${LINUX_VERSION}/${LINUX_VERSION}.${LINUX_SUBVERSION}/0002-Driver-change.patch \
    "<noinclude>

[[Category:How to customize software]]
[[Category:Distribution Package]]
{{PublicationRequestId | 8461 | 2018-08-29 | PhilipS}}</noinclude>
Line 1: Line 1:
  +
<noinclude>{{ApplicableFor
  +
|MPUs list=STM32MP13x, STM32MP15x
  +
|MPUs checklist=STM32MP13x,STM32MP15x
  +
}}</noinclude>
 
==Purpose of article==
 
==Purpose of article==
 
This article gives the main steps needed to add kernel customization within the Yocto build process (with a Distribution Package).
 
This article gives the main steps needed to add kernel customization within the Yocto build process (with a Distribution Package).