Building a custom Ubuntu kernel

README.md

I had a need to build a custom Ubuntu 18.04 kernel with a minor config option change.

The build script is based on these instructions from the Ubuntu wiki.

Differences from mainline

• Enables interrupt support for the PCA9535 GPIO controller
• Excludes the Nvidia DKMS modules

Building with Docker

It is recommended that the compilation be done in a Docker container:

# Ubuntu 18.04 Bionic
docker run --rm -it \
    -v "$(pwd):/output" \
    -e DISTRIB_CODENAME=bionic \
    -e KERNELVERS=4.15.0-122-generic \
    ubuntu:bionic \
    /output/build.sh

# Ubuntu 20.04 Focal
docker run --rm -it \
    -v "$(pwd):/output" \
    -e DISTRIB_CODENAME=focal \
    -e KERNELVERS=5.4.0-65-generic \
    ubuntu:focal \
    /output/build.sh

Note that it can take several hours to build the kernel and drivers.

The resulting .deb files will appear in the current directory.

Patching

The build script applies patches that are prefixed with the Ubuntu version codename, e.g., bionic-01-blah-blah.patch.

bionic-01-pca9535-interrupt-support.patch

This patch file was produced by running

    LANG=C fakeroot debian/rules editconfigs

and enabling the GPIO_PCA953X and GPIO_PCA953X_IRQ settings for the amd64 arch.
The Debian scripts propagate the old setting to all of the other architectures.

Because we are no longer building gpio_pca953x as a module, we also need to
disable a sanity check for the presence of the .ko file. This is done
dynamically in the build.sh script.

--------------------------------------------------------------------------------
diff -ru linux-4.15.0-orig/debian.master/config/amd64/config.flavour.generic linux-4.15.0/debian.master/config/amd64/config.flavour.generic
--- linux-4.15.0-orig/debian.master/config/amd64/config.flavour.generic	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/amd64/config.flavour.generic	2021-02-12 17:38:14.323530000 +0000
@@ -1,6 +1,7 @@
 #
 # Config options for config.flavour.generic automatically generated by splitconfig.pl
 #
+CONFIG_GPIO_PCA953X=y
 CONFIG_HZ=250
 # CONFIG_HZ_1000 is not set
 CONFIG_HZ_250=y
diff -ru linux-4.15.0-orig/debian.master/config/amd64/config.flavour.lowlatency linux-4.15.0/debian.master/config/amd64/config.flavour.lowlatency
--- linux-4.15.0-orig/debian.master/config/amd64/config.flavour.lowlatency	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/amd64/config.flavour.lowlatency	2021-02-12 17:38:14.314530000 +0000
@@ -1,6 +1,7 @@
 #
 # Config options for config.flavour.lowlatency automatically generated by splitconfig.pl
 #
+CONFIG_GPIO_PCA953X=m
 CONFIG_HZ=1000
 CONFIG_HZ_1000=y
 # CONFIG_HZ_250 is not set
diff -ru linux-4.15.0-orig/debian.master/config/arm64/config.common.arm64 linux-4.15.0/debian.master/config/arm64/config.common.arm64
--- linux-4.15.0-orig/debian.master/config/arm64/config.common.arm64	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/arm64/config.common.arm64	2021-02-12 17:38:40.079516000 +0000
@@ -134,6 +134,7 @@
 CONFIG_GPIO_GENERIC=y
 CONFIG_GPIO_GENERIC_PLATFORM=y
 CONFIG_GPIO_MB86S7X=m
+CONFIG_GPIO_PCA953X=m
 CONFIG_GPIO_TWL4030=m
 CONFIG_GPIO_TWL6040=m
 # CONFIG_HAVE_AOUT is not set
diff -ru linux-4.15.0-orig/debian.master/config/armhf/config.common.armhf linux-4.15.0/debian.master/config/armhf/config.common.armhf
--- linux-4.15.0-orig/debian.master/config/armhf/config.common.armhf	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/armhf/config.common.armhf	2021-02-12 17:38:40.078516000 +0000
@@ -117,6 +117,7 @@
 CONFIG_GPIO_GENERIC=y
 CONFIG_GPIO_GENERIC_PLATFORM=y
 CONFIG_GPIO_MB86S7X=m
+CONFIG_GPIO_PCA953X=m
 CONFIG_GPIO_TWL4030=y
 CONFIG_GPIO_TWL6040=y
 # CONFIG_HAVE_AOUT is not set
diff -ru linux-4.15.0-orig/debian.master/config/config.common.ubuntu linux-4.15.0/debian.master/config/config.common.ubuntu
--- linux-4.15.0-orig/debian.master/config/config.common.ubuntu	2021-02-12 17:36:12.591636000 +0000
+++ linux-4.15.0/debian.master/config/config.common.ubuntu	2021-02-12 17:38:40.073516000 +0000
@@ -3248,7 +3248,7 @@
 CONFIG_GPIO_MXC=y
 CONFIG_GPIO_OMAP=y
 CONFIG_GPIO_PALMAS=y
-CONFIG_GPIO_PCA953X=m
+CONFIG_GPIO_PCA953X_IRQ=y
 CONFIG_GPIO_PCF857X=m
 CONFIG_GPIO_PCH=m
 CONFIG_GPIO_PCI_IDIO_16=m
diff -ru linux-4.15.0-orig/debian.master/config/i386/config.common.i386 linux-4.15.0/debian.master/config/i386/config.common.i386
--- linux-4.15.0-orig/debian.master/config/i386/config.common.i386	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/i386/config.common.i386	2021-02-12 17:38:40.076516000 +0000
@@ -118,6 +118,7 @@
 CONFIG_GPIO_GENERIC=m
 CONFIG_GPIO_GENERIC_PLATFORM=m
 CONFIG_GPIO_MB86S7X=m
+CONFIG_GPIO_PCA953X=m
 CONFIG_GPIO_TWL4030=m
 CONFIG_GPIO_TWL6040=m
 CONFIG_HAVE_AOUT=y
diff -ru linux-4.15.0-orig/debian.master/config/ppc64el/config.common.ppc64el linux-4.15.0/debian.master/config/ppc64el/config.common.ppc64el
--- linux-4.15.0-orig/debian.master/config/ppc64el/config.common.ppc64el	2021-02-12 17:36:12.590636000 +0000
+++ linux-4.15.0/debian.master/config/ppc64el/config.common.ppc64el	2021-02-12 17:38:40.082516000 +0000
@@ -119,6 +119,7 @@
 CONFIG_GPIO_GENERIC=y
 CONFIG_GPIO_GENERIC_PLATFORM=m
 CONFIG_GPIO_MB86S7X=m
+CONFIG_GPIO_PCA953X=m
 CONFIG_GPIO_TWL4030=m
 CONFIG_GPIO_TWL6040=m
 # CONFIG_HAVE_AOUT is not set

build.sh

#!/bin/bash
set -eu -o pipefail
shopt -s nullglob

# For example: 4.15.0-122-generic
KERNELVERS="${KERNELVERS:-$(uname -r)}"

# For example: bionic
[ -z "$DISTRIB_CODENAME" ] && source /etc/lsb-release

# Drop into an interactive shell on error
function on_error {
    echo
    echo
    echo "An error occurred, you are being dropped into an interactive shell:"
    exec /bin/bash
}
trap on_error ERR

# Add source repositories
echo "deb-src http://archive.ubuntu.com/ubuntu ${DISTRIB_CODENAME} main" >> /etc/apt/sources.list
echo "deb-src http://archive.ubuntu.com/ubuntu ${DISTRIB_CODENAME}-updates main" >> /etc/apt/sources.list
apt update

# Keep tzdata from asking us questions during install
ln -snf /usr/share/zoneinfo/UTC /etc/localtime
echo UTC > /etc/timezone

# Install dependencies
apt build-dep -y linux-image-$KERNELVERS
apt install -y \
    bc \
    bison \
    cpio \
    curl \
    flex \
    dkms \
    gawk \
    kernel-wedge \
    kmod \
    libelf-dev \
    libssl-dev \
    lz4 \
    openssl

# Download the Linux sources
apt source linux-image-unsigned-$KERNELVERS
cd linux-*/

# Make scripts executable
chmod a+x debian/rules
chmod a+x debian/scripts/*
chmod a+x debian/scripts/misc/*

# Update the package version
sed -i -E '1 s/\((.*)\)/(\1+lrauv)/' debian.master/changelog

# Disable the module check
# https://wiki.ubuntu.com/KernelTeam/KernelMaintenance#Overriding_module_check_failures
PREV_ABIDIR=$(echo debian.master/abi/*/amd64)
sed -i "/gpio-pca953x/d" "$PREV_ABIDIR"/generic.modules

# Apply patches
for PATCH in "$(dirname "$0")/${DISTRIB_CODENAME}-"*.patch; do
    patch -p1 < "$PATCH"
done

# On Ubuntu Bionic, the build process tries to download an Nvidia driver package
# that has been pruned from the package repository. Since our system does not
# use any Nvidia components, we just disable it.
sed -i '/do_dkms_nvidia/ s/true/false/' debian.master/rules.d/amd64.mk

# Build
LANG=C fakeroot debian/rules clean
LANG=C fakeroot debian/rules binary-headers binary-generic

# Move built packages
mv ../*.deb "$(dirname "$0")"/

focal-01-pca9535-interrupt-support.patch

See bionic-01-pca9535-interrupt-support.patch for details.

On Focal, the debian.master/config/annotations file must also be updated.

--------------------------------------------------------------------------------
diff -ru linux-5.4.0-orig/debian.master/config/amd64/config.common.amd64 linux-5.4.0/debian.master/config/amd64/config.common.amd64
--- linux-5.4.0-orig/debian.master/config/amd64/config.common.amd64	2021-02-15 20:19:18.486654797 -0500
+++ linux-5.4.0/debian.master/config/amd64/config.common.amd64	2021-02-15 20:21:55.861268695 -0500
@@ -168,7 +168,6 @@
 CONFIG_GPIO_MAX7300=m
 CONFIG_GPIO_MAX732X=m
 CONFIG_GPIO_MB86S7X=m
-CONFIG_GPIO_PCA953X=m
 CONFIG_GPIO_PCF857X=m
 CONFIG_GPIO_SIOX=m
 CONFIG_GPIO_TPIC2810=m
diff -ru linux-5.4.0-orig/debian.master/config/config.common.ubuntu linux-5.4.0/debian.master/config/config.common.ubuntu
--- linux-5.4.0-orig/debian.master/config/config.common.ubuntu	2021-02-15 20:19:18.485654797 -0500
+++ linux-5.4.0/debian.master/config/config.common.ubuntu	2021-02-15 20:21:55.860268695 -0500
@@ -3607,6 +3607,7 @@
 CONFIG_GPIO_MXC=y
 CONFIG_GPIO_OMAP=y
 CONFIG_GPIO_PALMAS=y
+CONFIG_GPIO_PCA953X_IRQ=y
 CONFIG_GPIO_PCH=m
 CONFIG_GPIO_PCIE_IDIO_24=m
 CONFIG_GPIO_PCI_IDIO_16=m
diff -ru linux-5.4.0-orig/debian.master/config/annotations linux-5.4.0/debian.master/config/annotations
--- linux-5.4.0-orig/debian.master/config/annotations	2021-02-15 20:19:18.484654797 -0500
+++ linux-5.4.0/debian.master/config/annotations	2021-02-15 20:35:44.112182860 -0500
@@ -1456,7 +1456,7 @@
 CONFIG_GPIO_GW_PLD                              policy<{'arm64': 'm', 'armhf': 'm', 'ppc64el': 'm', }>
 CONFIG_GPIO_MAX7300                             policy<{'amd64': 'm', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
 CONFIG_GPIO_MAX732X                             policy<{'amd64': 'm', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
-CONFIG_GPIO_PCA953X                             policy<{'amd64': 'm', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
+CONFIG_GPIO_PCA953X                             policy<{'amd64': 'y', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
 CONFIG_GPIO_PCF857X                             policy<{'amd64': 'm', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
 CONFIG_GPIO_TPIC2810                            policy<{'amd64': 'm', 'arm64': 'm', 'armhf': 'm', 'i386': 'm', 'ppc64el': 'm', 's390x': 'n'}>
 CONFIG_GPIO_TS4900                              policy<{'armhf-generic': 'm'}>