Compiling the Kernel (NVIDIA DRIVE OS Linux)

This topic contains instructions for compiling the Linux Kernel Source in your Linux SDKproduct.

Prerequisites

You have installed the Kernel Source Code (already installed in Docker) and the toolchains:

sudo -E apt install  nv-driveos-linux-*_amd64.deb
sudo -E apt install nv-driveos-foundation-toolchains-*_amd64.deb

The top-level directory layout has this appearance:

drive-foundation
drive-linux
drive-linux_src
toolchains

To compile the kernel

Set up the environment macros: The LOCAL_VERSION environment variable appends -tegra to the kernel version and modules.

export ARCH=arm64
export CROSS_COMPILE=${PWD}/toolchains/aarch64--glibc--stable-2022.03-1/bin/aarch64-buildroot-linux-gnu-
export LOCALVERSION="-tegra"
export NV_BUILD_KERNEL_OPTIONS="5.10"

Set the kernel source directory as the current working directory:
```
cd <top>/drive-linux/kernel/source/oss_src
```
Enter the following command to apply the rt-patches.
```
bash kernel/scripts/rt-patch.sh apply-patches
```
Create an output directory, and then configure the kernel for the board:
```
mkdir out-linux
make -C kernel O=${PWD}/out-linux clean
```
If prompted, install the packages:
```
sudo apt-get install imagemagick graphviz dvipng python3-venv fonts-noto-cjk latexmk librsvg2-bin texlive-xetex flex bison -y
```
/usr/bin/python3 -m venv sphinx_2.4.4
. sphinx_2.4.4/bin/activate
```
pip install -r <top>/drive-linux/kernel/source/oss_src/kernel/Documentation/sphinx/requirements.txt
```
sudo apt-get install flex
sudo apt-get install bison
Add the following command:
```
make -C kernel O=${PWD}/out-linux tegra_defconfig
```
Build the kernel:
```
make -j3 -C kernel O=${PWD}/out-linux
```
Note:
If the preceding command fails, enter the make command without the j<number> option.
To flash the built images, copy the uncompressed (Image) kernel images to the kernel top directory with the following command:
```
sudo cp ${PWD}/out-linux/arch/arm64/boot/Image 
<top>/drive-linux/kernel/preempt_rt/images/
```
CAUTION:
Before copying the new kernel images, create a backup of the default kernels provided.
Consolidate the built kernel modules in the build directory with the following commands:
```
export INSTALL_MOD_PATH=${PWD}/out-linux
make -C kernel O=${PWD}/out-linux modules_install
```
Deactivate Sphinx with the following command:
```
$ deactivate
```
Copy the built modules to the root filesystem path with the following commands:
1. Copy the built modules to the SDK kernel modules path:
```
sudo cp -a ${PWD}/out-linux/lib/modules/* <top>/drive-linux/kernel/preempt_rt/modules
```
2. To copy the updated modules into the root filesystem, use the following Build-FS steps:
  1. Create a Build-FS JSON with the following content:
```
$ vim update_rfs.CONFIG.json
{
    "OS": "linux",
    "Output": "driveos-updated-rfs",
    "Base": "${BASE_DIR}/targetfs.img",
    "CopyTargets": [
        "${COPYTARGETYAML_DIR}/copytarget-kernel-modules.yaml"
    ]
}
```
  2. Execute Build-FS with the preceding configuration to rebuild the filesystem. Set NV_WORKSPACE to opt of SDK install directory (containing drive-linux directory).
```
$ sudo -E /usr/bin/python3 -B /opt/nvidia/driveos/common/filesystems/build-fs/17/bin/build_fs.py -w ${NV_WORKSPACE}/ -i $PWD/update_rfs.CONFIG.json -o ${NV_WORKSPACE}/drive-linux/filesystem/targetfs-images/
$ sudo rm -f ${NV_WORKSPACE}/drive-linux/filesystem/targetfs.img
$ sudo ln -s ${NV_WORKSPACE}/drive-linux/filesystem/targetfs-images/driveos-updated-rfs.img ${NV_WORKSPACE}/drive-linux/filesystem/targetfs.img
```
  3. Flash the target using the SDK Bootburn tool.
Note:
To ensure that all modules are loaded, at the target side, execute these commands:
```
depmod -a
sync
```
The sync command must be executed as superuser. From the next boot onward, the kernel modules are auto-loaded on boot.
If there is a change in the device tree source files, copy the newly generated DTB files:
```
sudo cp ${PWD}/out-linux/arch/arm64/boot/dts/nvidia/<dtb_file>
<top>/drive-linux/kernel/preempt_rt/
```