3.2.1. Users Guide
3.2.1.1. Overview
This document will cover the basic steps for building the Linux kernel.
Install host dependencies
To install host dependencies for building TI Linux kernel source (standalone) on Ubuntu 22.04+, run the following command in the terminal prompt:
sudo apt install git xz-utils build-essential flex bison bc libssl-dev libncurses-dev
3.2.1.2. Getting the Kernel Source Code
The easiest way to get access to the kernel source code is by downloading and installing the Processor SDK Linux J7200. You can download the latest Processor SDK Linux J7200 installer from Jacinto7-Linux-SDK-Download-page. Once installed, the kernel source code is included in the SDK’s board-support directory. For your convenience the sources also includes the kernel’s git repository including commit history. Alternatively, Kernel sources can directly be fetched from GIT.
3.2.1.3. Preparing to Build
Note
Run these commands from the root of the kernel tree unless otherwise
specified. The root of the kernel tree is the top-level directory, which
you can identify by the presence of the MAINTAINERS file.
3.2.1.3.1. Setup Cross Compile Environment
Important
When using the GCC toolchain provided with the SDK or stand alone from TI that you do
NOT source the environment-setup file included with the toolchain when
building the kernel. Doing so will cause the compilation of host side components within
the kernel tree to fail.
3.2.1.3.2. Cleaning the Kernel Sources
Prior to compiling the Linux kernel it is often a good idea to make sure that the kernel sources are clean and that there are no remnants left over from a previous build.
Note
The next step will delete any saved .config file in the kernel tree as
well as the generated object files. If you have configured the kernel
before and do not want to lose your existing configuration you should
save a copy of the configuration file (.config) before proceeding.
The command to clean the kernel is:
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" distclean
3.2.1.4. Configuring the Kernel
Before compiling the Linux kernel it needs to be configured to select what components will become part of the kernel image, which components will be build as dynamic modules, and which components will be left out all together. This is done using the Linux kernel configuration system.
It is often easiest to start with a base default configuration and then customize it for your use case if needed. Apply Linux kernel configurations with a command of the form:
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" <defconfig>
3.2.1.4.1. Using Default Configurations
For this sdk, the defconfig found in arch/arm64/configs is used to create the prebuilt
files. We recommend users to use this kernel configuration (or at least use it
as a starting point).
For example, to apply the recommended kernel configuration for K3 devices, use:
For Linux,
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" defconfig ti_arm64_prune.config
For RT-Linux,
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" defconfig ti_arm64_prune.config ti_rt.config
The config fragments found in <path-to-ti-linux-kernel>/kernel/configs can be used to trim/add features when building a kernel that targets only TI EVMs. Append a config fragment to the end of “make” command like above to add/remove features.
After the configuration step has run the full configuration file is saved to the root of the kernel tree as .config. Any further configuration changes are based on this file until it is cleaned up by doing a kernel clean as mentioned above.
3.2.1.4.2. Customizing the Configuration
When you want to customize the kernel configuration the easiest way is to use the built in kernel configuration systems. One popular configuration system is menuconfig. menuconfig is an ncurses based configuration utility.
To invoke the kernel configuration you simply use a command like:
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" <config type>
i.e. for menuconfig the command would look like
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" menuconfig
Once the configuration window is open you can then select which kernel components should be included in the build. Exiting the configuration will save your selections to a file in the root of the kernel tree called .config.
3.2.1.5. Compiling the Sources
3.2.1.5.1. Compiling the Kernel
By default U-boot expects to boot kernel Image, DTB, and DTOs found in root/boot of the
SD card if using SD/MMC boot. The exception is for HS-SE (High Security - Security Enforced)
devices where the FIT image (Flattened Image Tree) named fitImage will boot by default.
The FIT image includes the kernel Image, DTB, and DTOs. Booting with the FIT image could be
enabled/disabled by setting/resetting u-boot environment variable boot_fit. If boot_fit is set
to 1, then u-boot will boot the FIT image found in root/boot of the SD card.
Once the kernel has been configured it must be compiled to generate the bootable kernel Image
as well as any dynamic kernel modules that were selected. To rebuild kernel Image to boot as
is or for FIT image boot, use this command:
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" Image
This will result in a kernel image file being created in the
arch/arm64/boot/ directory called Image.
3.2.1.5.2. Compiling the Device Tree Binaries
Each TI evm has an unique device tree
binary file required by the kernel. Therefore, you will need to build
and install the correct dtb for the target device. TI device tree files
are located in arch/arm64/boot/dts/ti. Below list various TI evms and the
matching device tree file.
Boards |
Device Tree File |
|---|---|
AM62Lx EVM |
k3-am62l3-evm.dts |
BeagleBadge |
k3-am62l3-badge.dts |
AM62Px SK |
k3-am62p5-sk.dts |
AM62Ax SK |
k3-am62a7-sk.dts |
AM62Dx EVM |
k3-am62d2-evm.dts |
AM62x LP SK |
k3-am62-lp-sk.dts |
Beagle Play |
k3-am625-beagleplay.dts |
AM62SIP SK / AM62x SK |
k3-am625-sk.dts |
AM64x EVM |
k3-am642-evm.dts |
AM64x SK |
k3-am642-sk.dts |
AM65x EVM / AM65x IDK |
k3-am654-base-board.dts, daughter cards use .dtso files |
J721e EVM |
k3-j721e-common-proc-board.dts |
J721e SK |
k3-j721e-sk.dts |
J7200 EVM |
k3-j7200-common-proc-board.dts |
J721S2 EVM |
k3-j721s2-common-proc-board.dts |
AM68 SK |
k3-am68-sk-base-board.dts |
J784S4 EVM |
k3-j784s4-evm.dts |
AM69 SK |
k3-am69-sk.dts |
J722S EVM |
k3-j722s-evm.dts |
To build an individual device tree file find the name of the dts file for the board you are using and replace the .dts extension with .dtb. Then run the following command:
make DTC_FLAGS=-@ ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" ti/<dt filename>.dtb
The compiled device tree file with be located in arch/arm64/boot/dts/ti.
For example, the AM64x EVM device tree file is named
k3-am642-evm.dts. To build the device tree binary you would run:
make DTC_FLAGS=-@ ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" ti/k3-am642-evm.dtb
Alternatively, you can build every device tree binary with command
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" dtbs
3.2.1.5.3. Compiling the Kernel Modules
By default the majority of the Linux drivers used in the sdk are not
integrated into the kernel image file Image. These drivers are built as
dynamic modules. The command to build these modules is:
make ARCH=arm64 CROSS_COMPILE="$CROSS_COMPILE_64" modules
This will result in .ko (kernel object) files being placed in the kernel tree. These .ko files are the dynamic kernel modules.
Note
If you make a change to the kernel that requires you to recompile the kernel, then you should also recompile the kernel modules and reinstall the kernel modules. Otherwise your kernel modules might refuse to load, which will result in a loss of functionality.
3.2.1.6. FIT Image
3.2.1.7. Installing the Kernel
Once the Linux kernel, dtb files and modules have been compiled they must be installed. In the case of the kernel image this can be installed by copying the kernel image file to the location where it is going to be read from. The device tree binaries should also be copied to the same directory that the kernel image was copied to.
3.2.1.7.1. Installing the Kernel Image and Device Tree Binaries
cd <kernel sources dir>
sudo cp arch/arm64/boot/Image <rootfs path>/boot
sudo cp arch/arm64/boot/dts/ti/<dt file>.dtb <rootfs path>/boot/dtb/ti
For example, if you wanted to copy the kernel image and AM64x EVM device tree file to the rootfs partition of a SD card you would enter the below commands:
cd <kernel sources dir>
sudo cp arch/arm64/boot/Image /media/$USER/rootfs/boot
sudo cp arch/arm64/boot/dts/ti/k3-am642-evm.dtb /media/$USER/rootfs/boot/dtb/ti
Starting with U-boot 2013.10, the kernel and device tree binaries are read from
the root file system’s boot directory when booting from MMC/EMMC. (NOT from the
/boot/ partition on the MMC). This would mean you copy the kernel image and device
tree binaries to /media/$USER/rootfs/boot instead of /media/$USER/boot.
Here, $USER is the username of the user on the host machine where the SD card
is mounted.
3.2.1.7.2. Installing the Kernel Modules
To install the kernel modules you use another make command similar to the others, but with an additional parameter which give the base location where the modules should be installed. This command will create a directory tree from that location like lib/modules/<kernel version> which will contain the dynamic modules corresponding to this version of the kernel. The base location should usually be the root of your target file system. The general format of the command is:
sudo make ARCH=arm64 INSTALL_MOD_PATH=<path to root of file system> modules_install
For example if you are installing the modules on the rootfs partition of the SD card you would do:
sudo make ARCH=arm64 INSTALL_MOD_PATH=/media/$USER/rootfs modules_install
Here, $USER is the username of the user on the host machine where the SD card
is mounted.
Note
Append INSTALL_MOD_STRIP=1 to the make modules_install command to reduce the size of the resulting installation