What You Will Learn

• A single map of every stage from getting kernel source to a booted target
• How to decide between building a driver as a module or built-in for an embedded target
• A reusable pre-flight checklist you can run before any new board bring-up
• What’s still missing after a successful boot, and why that’s the next topic

Prerequisites

• Having followed the earlier lectures in this free linux kernel development course chapter, from getting kernel source through booting a board kernel

The Full Porting Pipeline, End To End

Every board bring-up, however different the SoC, follows the same shape. Source comes from either mainline, a vendor tree, or a third party BSP. That source is configured for the target with Kconfig, built with Kbuild into an image plus any modules and device tree blobs, and then handed to the target by a bootloader that identifies the hardware before jumping into the kernel.

That final box, root filesystem, is deliberately unfinished here — a kernel that boots but finds no usable root filesystem stops with a kernel panic, and that hand-off is exactly where the next chapter of this course begins.

Modules Versus Built-In, Revisited

This decision comes up on nearly every board, so it’s worth having a firm rule of thumb rather than re-deriving it each time.

A Reusable Pre-Flight Checklist

Here is a small original shell script you can drop into any board bring-up repository. It doesn’t touch the kernel tree itself — it just verifies your build environment agrees with itself before you spend ten minutes on a build only to find ARCH was never exported.

#!/bin/sh
# ep_kernel_preflight.sh — sanity-check a cross build environment
set -e

: "${ARCH:?ARCH is not set, e.g. export ARCH=arm}"
: "${CROSS_COMPILE:?CROSS_COMPILE is not set, e.g. export CROSS_COMPILE=arm-linux-gnueabihf-}"

if ! command -v "${CROSS_COMPILE}gcc" >/dev/null 2>&1; then
    echo "ERROR: ${CROSS_COMPILE}gcc not found on PATH" >&2
    exit 1
fi

echo "ARCH=${ARCH}"
echo "CROSS_COMPILE=${CROSS_COMPILE}"
"${CROSS_COMPILE}gcc" --version | head -n1
echo "Preflight OK — safe to run make defconfig"

Expected output on a correctly configured host:

$ export ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf-
$ ./ep_kernel_preflight.sh
ARCH=arm
CROSS_COMPILE=arm-linux-gnueabihf-
arm-linux-gnueabihf-gcc (Ubuntu 13.2.0) 13.2.0
Preflight OK — safe to run make defconfig

Common Mistakes Across This Whole Chapter

• Starting from a random vendor tree instead of checking whether mainline already supports the SoC — mainline gets long-term maintenance, vendor trees often don’t.
• Configuring everything as a module on a board where nothing ever changes after manufacturing, adding unnecessary boot-time fragility.
• Not distinguishing a porting failure (nothing on the console) from a root filesystem failure (clean version banner, then a panic) — they need completely different debugging.

Best Practices Recap

• Start from the closest matching mainline board support and diff outward, rather than writing from a blank defconfig.
• Keep board-specific patches rebased and out-of-tree code to an absolute minimum so future kernel upgrades stay tractable.
• Treat the porting pipeline as one reproducible pipeline (source → config → build → boot), not four disconnected manual steps.

Additional Reading

• The kernel’s own in-tree documentation at Documentation/admin-guide/README.rst
• Your SoC vendor’s board integration guide, for anything genuinely hardware-specific that mainline docs can’t cover

Summary And Conclusion

The Linux kernel’s configurability is exactly what lets one codebase span a tiny sensor node and a full server. Porting to a new board is really just: get the right source, configure it, build it, and let a bootloader identify the hardware correctly. Where boards differ is only in how much of that work is already done for you by mainline versus how much you have to do yourself. A booted kernel is a milestone, not the finish line — it still needs a root filesystem to actually run any user-space program, which is exactly where this course picks up next.

FAQ