I would like to add various kernel command line arguments (e.g isolcpus=3) to the yocto build. I’ve searched the various layers/recipes in Yocto and can’t seem to find the correct location. What is the correct recipe to append/file to patch?
(I was able to do this using torizoncore-builder but would like to integrate it into our yocto build.)
Hi, I’m the Toradex AI Assistant.
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To add kernel command line arguments to your Yocto build, you need to create a .bbappend file for the Linux kernel recipe in your custom meta layer. The approach depends on your System on Module (SoM) architecture(1).
Create the following directory structure and file in your custom meta layer(1):
$ cd ../layers/meta-customer/
$ mkdir -p recipes-kernel/linux/linux-toradex
$ touch recipes-kernel/linux/linux-toradex/linux-toradex%.bbappend
Create the directory and append file for TI modules(1):
recipes-kernel/linux/linux-toradex-ti.bbappend file: linux-toradex-ti%.bbappendIn your .bbappend file (e.g., recipes-kernel/linux/linux-toradex%.bbappend), you can add kernel arguments through the kernel configuration. Here’s the basic structure(1):
FILESEXTRAPATHS:prepend := "${THISDIR}/linux-toradex:"
# Prevent the use of in-tree defconfig
unset KBUILD_DEFCONFIG
SRC_URI += "\
file://defconfig \
"
Create a defconfig file in your recipes-kernel/linux/linux-toradex/ directory and add your kernel command line arguments. For your specific example with isolcpus=3, you would modify the kernel configuration to include this parameter.
If you’re building Torizon OS with Yocto, you can also reference how TorizonCore Builder handles kernel arguments. The tool uses device tree overlays to set custom kernel arguments(2), creating a custom-kargs_overlay.dts that gets compiled and applied(2).
Your final directory structure should look like this(1):
meta-customer/
├── conf
│ └── layer.conf
└── recipes-kernel
└── linux
└── linux-toradex (or linux-toradex-ti for TI SoMs)
├── linux-toradex%.bbappend
└── defconfig
Make sure your custom meta layer is properly initialized as a Git project if you’re building Torizon OS, as this is mandatory for OSTree integration(1).
Best regards, Toradex AI Assistant.
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Hi @ToradexAI
I would like to explore the device tree overlay method. Can you elaborate more on the contents of the dts file and the steps to integrate it into the torizon yocto build?
You can use device tree overlays to set kernel command line arguments like isolcpus=3. Here’s how to create the overlay and integrate it into your Yocto build:
Create a device tree overlay source file (.dts) with the /plugin/ directive (1). Here’s the basic structure for adding kernel arguments:
/dts-v1/;
/plugin/;
/ {
compatible = "toradex,<your-module>";
fragment@0 {
target-path = "/chosen";
__overlay__ {
bootargs-append = "isolcpus=3";
};
};
};
The overlay must be denoted with /plugin/; in the header (2). Replace <your-module> with your specific Toradex module (e.g., verdin-imx8mp, colibri-imx8x) (1).
You can use this template for pin muxing or other customizations (1):
/dts-v1/;
/plugin/; //Indicates a Device Tree Overlay
// Header file with pin definitions
#include <soc-pinfunc.h>
/ {
compatible = "toradex,apalis-imx8"; // Set hardware compatibility
};
&iomuxc {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl-originally-in-device-tree>, <&pinctrl_my_pins>; // Pin group available in userspace i.e. as GPIO
name-of-som {
pinctrl_my_pins: my_muxgrp {
fsl,pins = <
PIN_NAME_PIN_MUX PAD_CTRL // PINS
>;
};
};
};
&node {
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_my_pins>; // Pin group used in genericPeripheral
status = "okay";
};
There are two recipes that handle device tree overlays (2):
meta-toradex-bsp-common/recipes-kernel/linux/device-tree-overlays-mainline_git.bb (2)meta-toradex-nxp/recipes-kernel/linux/device-tree-overlays_git.bb (2)You can write your own bbappends to add your device tree overlays repository (2).
Create a bbappend file with this structure (2):
FILESEXTRAPATHS:prepend := "${THISDIR}/device-tree-overlays:"
CUSTOM_OVERLAYS_SOURCE = " \
my-device-tree_overlay.dts \
"
CUSTOM_OVERLAYS_BINARY = " \
my-device-tree_overlay.dtbo \
"
SRC_URI += " \
file://my-device-tree_overlay.dts \
"
TEZI_EXTERNAL_KERNEL_DEVICETREE += " \
${CUSTOM_OVERLAYS_BINARY} \
"
TEZI_EXTERNAL_KERNEL_DEVICETREE_BOOT = " \
${CUSTOM_OVERLAYS_BINARY} \
"
do_collect_overlays:prepend() {
for DTS in ${CUSTOM_OVERLAYS_SOURCE}; do
cp ${WORKDIR}/${DTS} ${S}
done
}
The class meta-toradex-bsp-common/classes/image_type_tezi.bbclass uses the variable TEZI_EXTERNAL_KERNEL_DEVICETREE_BOOT to add overlays that will be applied during boot time (2).
You can find the variable settings using grep in the layers directory (2):
$ cd <yocto projet setup>
$ grep -nre "TEZI_EXTERNAL_KERNEL_DEVICETREE_BOOT" layers/*
For evaluation and development, you can use TorizonCore Builder’s dto command (1):
$ torizoncore-builder dto apply device-trees/overlays/<your-custom-device-tree-overlay.dts>
For production, use the build.yaml file approach (1):
customization:
device-tree:
include-dirs:
- device-trees/include/
overlays:
add:
- device-trees/overlays/<your-custom-device-tree-overlay.dts>
This enables the build command to compile and deploy the DTOs to your customized image (1).
device-tree-overlays folder at the same directory as your bbappend (2)Best regards, Toradex AI Assistant.
Did you like my answer?
If I answered your question, please tick the “Solution” checkbox.
For follow-up questions to me, please use @ToradexAI in your post.