Let's code a Linux Driver - 1: Hello World Linux Kernel Module 

Monkey see monkey do. I wish the Linux people would learn this. RU-vid is full of great presentations by the Linux foundation on various interesting things but when you sit down to actually test the stuff they presented you are immediately stuck. They spend 1h talking about something that 1 % of the listeners can apply. If they just did what they are trying to present live it would be a thousand times more useful.

eh ya zmeely

Thank you. Yes, maybe later this year I want to do a session about Cross Compiling. But therefore I would like to use an industrial grade SoC on an evaluation board. And I am still looking for an affordable candidate.

Thank you. Yes, I can recommend Linux Device Drivers 3rd edition. It is a little bit old, bit the concepts still apply. makelinux.net/ldd3/ There are more recent books available, but I haven't read them, so I can't really recommend them. Embetronix also has a great series of written tutorials to Linux Drivers. embetronicx.com/tutorials/linux/device-drivers/linux-device-driver-part-1-introduction/

Thanks a lot @@johannes4gnu_linux96 Please add more content, your tutorials are really neat and easy to follow.

It resovles to something similar like this: /lib/modules/6.10.5-arch1-1/build If you are missing the build folder, you have to install the linux kernel headders, e.g. with "sudo apt install raspberrypi-linux-headers" on a raspberry pi.

Thank you for our feedback and the info :) I mentioned this "preparation steps" in the first video, I have done on this "Let's code a Linux Driver" session: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-x1Y203vH-Dc.html But it is also good to mention it here.

Well, both methods have their advantages and disadvantages. I choose to use a raspberry pi, because of the following reasons: - a lot of people have RPis and know how to use them - Good documentation - Powerful computers (Mine has a Quad core A53 and 1GB of memory, which is a lot for an embedded device!) - Full featured linux distro (with package manager, python, compiler, ... already available) - RPi has all the important interfaces (SPI, GPIO, I2C, ...) So, I choose the RPi because I wanted to use a comfortable computing platform, where I could just start to develop my Kernel Modules. I didn't want to use *Cross-Compiling* or *Virtualization with QMENU* because this are quite difficult topics and I just want to focus on the Kernel-Module-Programming. I believe for a beginner this approach is more straight forward and easier. But if your target for your project is not a RPi, using your hardware, which is maybe not as powerful as the RPi, Yocto and Cross-Compiling is the way to go. Using Yocto has the advantages you can compile everything yourself (and apply some Kernel-Patches you are interested in, e.g. Realtime patches), you only have the programs onboard, you really need, you can use a custom Device Tree and your SD-Card Image will be a lot smaller then Raspbian. But going this way you loose a lot of comfort from the RPi, e.g. most Yoctos don't have a package manager as powerfull as apt, most of them don't have python or a compiler installed, ... With Yocto you really get a minimal Linux for an embedded system with all up- and downsides. You have to cross compile, because the compilation is to resource heavy for your tiny hardware, etc. I would only use Virtualization with QMENU, if you don't have the hardware available and you want to start developing or if you have to debug a lot and you don't have a good (and most of the time expensive) JTAG-HW-Debugger. So, for beginners, I would recommend to use a RPi. It will offer you a lot of comforts and a lot of interfaces. But if you don't mind the interfaces, you can develop Kernel modules on a normal x86-PC too! All of my tutorials, where I do not need I2C, SPI or GPIOs will work fine there too! Then, when you are more familiar with the Kernel-Programming and you have a project with a different Target-HW, then go the next step and start using Yocto, Cross-Compiling and Virtualization.

​@@johannes4gnu_linux96 Thanks for your detailed answer which cleared my mind a lot, till now I have learned all of your device driver videos and from other channels, so I have written GPIO, USB, I2C and many more drivers. i have noticed that in all of that i just take any hardware attached with my rpi and start writing code. For example, In USB driver I attached my mobile phone with usb to rpi, and got the vendor id, product id with lsusb , and then wrote a driver to probe, disconnect and table, and get a minor number of device in output. and the same goes with the other drivers also. But I am unable to understand the need of writing drivers, in GPIO driver we can simply write c code or anything, what is the need of writing kernel device drivers. i have read my articles but I don't understand them completely, so I decided to ask you because your previous reply helped me a lot.

It depends on your makefile. In the makefile, I am using in the video, I just set some variables and then call another makefile located in /lib/modules/$(shell uname -r)/build. Here everything about how to build the module is defined. The makefile is only smart enough to build every c file it finds in the folder, if you specify it in the makefile. In the case of our makefile it isn't.

Have you installed the Kernel headers? On Ubuntu run: sudo apt-get install linux-headers-$(uname -r) Are You using the same makefile as I do? The path /home/Jonathan/Linux_Kernel/5.* Looks wrong.

@@johannes4gnu_linux96 Cool it seems to work! but i didn't get .ko file : make -C /lib/modules/5.3.0-28-generic/build M=/home/jonathan/Linux_Kernel modules make[1]: Entering directory '/usr/src/linux-headers-5.3.0-28-generic' Building modules, stage 2. MODPOST 0 modules make[1]: Leaving directory '/usr/src/linux-headers-5.3.0-28-generic'

Update: it produces .ko file. i had spelling error in make file

@@Jonathan-ru9zl Good to hear it works.

I don't understand what you mean here.But you can find videos where I am overloading syscalls for device files in my playlist.

Yes, all of my driver tutorial videos (if they are not outdated like the first SPI and I2C videos) should be compile-able on any Linux system. That's one of the tasks of an operating system to give us a hardware abstraction layer. When you come to drivers accessing hardware (e.g. accessing GPIOs) maybe you have to change something (e.g. pin numbers), but in general it should work.

It look like the kernel modules are not installed. Are you using a TI EVM or beaglebone with (Yocto) Linux? For the raspberry pi maybe this helps: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RJr0c4dpKxI.html

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RJr0c4dpKxI.html This should solve the problem

Most of the videos should work except for those in which I access pheripherals Like GPIOs, I2C, SPI, ... These are normally not so easy accessable on a Standard PC Like on the Raspberry Pi.

@@johannes4gnu_linux96 Thank you very much, I will continue watching your videos.

You are welcome. To help you, I need more information: - What is your target (Raspberry Pi)? - Are you doing the compiling on the target (on the RPi) or are you using cross compiling? - If you are on a RPi, have you followed the tips shown here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RJr0c4dpKxI.html I know this error from doing cross compiling and the Kernel Version on my Target didn't match with the Kernel I used to compile my sources.

@@johannes4gnu_linux96 Oh okay, I am actually on Ubuntu virtual machine. I looked around before I commented here, I am sure the kernel I am running and the target kernel during compilation is the same, because the output of uname -r command matches.

Thank you. Run this Commando: sudo apt install raspberrypi-kernel-headers This should solve the problem.

@@johannes4gnu_linux96 thanks Reading package lists... Done Building dependency tree Reading state information... Done raspberrypi-kernel-headers is already the newest version (1:1.20210831-3~buster). 0 upgraded, 0 newly installed, 0 to remove and 51 not upgraded.

@@imranrajjad7028 i m having same problem help me

make -C /lib/modules/5.10.63-v7+/build M=/home/pi/Programming/Linux_Driver_Tutorial modules make[1]: *** /lib/modules/5.10.63-v7+/build: No such file or directory. Stop. make: *** [Makefile:3: all] Error 2

@@johannes4gnu_linux96 error still continue :( make -C /lib/modules//build M=/home/pi/hello modules make[1]: *** /lib/modules//build: No such file or directory. Stop. make: *** [Makefile:4: all] Error 2

ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RJr0c4dpKxI.html This should solve the problem

Looks Like the Kernel headers are not installed correctly. Watch this: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-RJr0c4dpKxI.html

Yes, if you indicate the source it is ok from my side.

@@johannes4gnu_linux96 thank you , no problem!