Linux: Compiling a kernel device driver in standalone fashion

Question

I'm compiling linux for an ARM board. I need to make some customized changes into an existing driver code present in the kernel repository and reload the driver.

I was expecting to find a ".ko" file in the driver directory after doing the make, but no such file exists. Apparently uImage/device tree image compilation doesn't work that way.

Do I need to write my own Makefile for standalone device driver compilation?

It may be a silly question, but sorry I'm pretty new to kernel/device drivers.

EDIT: I followed the process outlined here: http://odroid.com/dokuwiki/doku.php?id=en:c1_building_kernel After git checkout and installing the cross-compiler(arm-linux-gnueabihf-gcc 4.9.2), I issue the basic make comands

$ make odroidc_defconfig
$ make -j4
$ make -j4 modules
$ make uImage

All the steps are successful. The last few lines of log look like

KSYM    .tmp_kallsyms1.o
KSYM    .tmp_kallsyms2.o
LD      vmlinux
SORTEX  vmlinux
SYSMAP  System.map
OBJCOPY arch/arm/boot/ccImage
Kernel: arch/arm/boot/ccImage is ready
Image arch/arm/boot/ccImage.lzo is ready
UIMAGE  arch/arm/boot/uImage
Image Name:   Linux-3.10.72
Created:      Sat Mar 28 22:44:45 2015
Image Type:   ARM Linux Kernel Image (lzo compressed)
Data Size:    5459649 Bytes = 5331.69 kB = 5.21 MB
Load Address: 00208000
Entry Point:  00208000
Image arch/arm/boot/uImage is ready

EDIT 2: Path to the driver code https://github.com/hardkernel/linux/tree/odroidc-3.10.y/drivers/amlogic/efuse

I assume you wanted to say "but no such file exists". What commands did you issue to build the kernel object? And what was the output? — mcleod_ideafix
Agree on wondering what the build process and output was, additionally is it possible your build system is configured to dump output somewhere out of tree? You might try using find somepath -name "*.ko" Also make sure that the Makefile in the module source directory has the module of interest enabled, either permanently or via a config option which is on. If you get really uncertain, put a #error or something in the source and see if the build breaks - if it doesn't, your source code isn't being processed. — Chris Stratton
@ChrisStratton - Doing find . -name "*.ko" gives me a list of "ko" files, but none for the driver I'm interested in. And that driver DOES gets compiled(ex. Adding a syntax error aborts the compilation) — Neo
Show the Makefile of the driver in question, or better yet deep link to the source tree where it lives. Are you sure that it is supposed to be built as a module, and not statically linked into the kernel? Show the state of any config options it depends on. — Chris Stratton

Chris Stratton Chris Stratton · Accepted Answer · 2015-03-28T17:44:01

Examining your Makefile

#                             
# Makefile for eFuse.         
#                             

obj-$(CONFIG_EFUSE) += efuse_bch_8.o efuse_version.o efuse_hw.o efuse.o

We learn that the code can be built as either a loadable module, or permanently linked into the kernel itself.

Examining odroidc_defconfig from branch odroidc-3.10.y-android mentioned in your instructions we find

#
# EFUSE Support
#
CONFIG_EFUSE=y

With the "y" indicating that the code is to be linked into the driver. Had it instead said "m" it would be built as a module.

It's possible you could change that in the kernel config, but it might also cause problems if there's nothing setup to load the module before it is needed.

Likely simply installing the newly built kernel with the code already linked inside (ie, forgetting about the module idea) will work.

Linux: Compiling a kernel device driver in standalone fashion

2 Answers