** Objectives of this tuto is to build module compatible with current AKF kernel **

Kernel version of the force is 5.15.89-inmusic-2023-01-18-rt56


To build same kernel/module as force you'll need : 

 - Arm processor to build source, you can cross compile but it is easier to do it on an arm processor ( so you can use raspberry pi, arm chromebook etc.., on my side i use an ARM chromebook with a RK3288; same chip as akaiforce. 

 - Linux kernel source version 5.15 
[[https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.15.tar.xz]]

 - Linux kernel patch version 5.15.86 
[[https://cdn.kernel.org/pub/linux/kernel/v5.x/patch-5.15.86.xz]]

 - Linux incremental patch 5.15.86-87 
[[https://cdn.kernel.org/pub/linux/kernel/v5.x/incr/patch-5.15.86-87.xz]]

 - Linux incremental patch 5.15.87-88  
[[https://cdn.kernel.org/pub/linux/kernel/v5.x/incr/patch-5.15.87-88.xz]]

 - Linux incremental patch 5.15.88-89
[[https://cdn.kernel.org/pub/linux/kernel/v5.x/incr/patch-5.15.88-89.xz]] 

 - Linux realtime ( RT ) patch 5.15.86-rt56 
[[https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.86-rt56.tar.gz]]

 - dos2unix tool (apt-get) 
 
 - config file from AKF kernel.


Extract kernel source 5.15 with 
<code> tar -xf linux-5.15.tar.xz </code>

it will create a folder linux-5.15, this is what i call __**source tree**__ ( or kernel source ) 

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/KernelSourceFile.JPG}}



Unzip all patches

<code>
unxz patch-5.15.86.xz 
unxz patch-5.15.86-87.xz
unxz patch-5.15.87-88.xz 
unxz patch-5.15.88-89.xz 
tar xvzf patches-5.15.86-rt56.tar.gz
</code>

You should have something like this : 

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/KernelFilesList.JPG}}


apply dos2unix on each patches, and in folder patches ( extracted from patches-5.15.86-rt56)
<code>dos2unix patch-5* 
cd patches 
dos2unix *.patch </code>

__Go to kernel source__ and patch like below 


<code>cd linux-5.15
/linux-5.15$ patch -p1 < ../patch-5.15.86
/linux-5.15$ cat ../patches/*.patch | patch -p1
/linux-5.15$ patch -p1 < ../patch-5.15.86-87
/linux-5.15$ patch -p1 < ../patch-5.15.87-88
/linux-5.15$ patch -p1 < ../patch-5.15.88-89
</code>

Order is : 5.15.86, Rtpatch 5.15.86-rt56 , 5.15.86-87 , 5.15.87-88 , 5.15.88-89

Now we have 5.15.89-rt56 8-)


__stay in source tree folder :__ 

Change localversion in file localversion-rt
<code> change -rt56 to -inmusic-2023-01-18-rt56 </code>
{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/localversion_change.JPG}}


Get kernel config from AkaiForce kernel : this file is named config.gz and we can find it in /proc/ (on AKF )
unzip the file with gunzip
<code>gunzip config.gz </code>

It gives a file named "config"  

Copy this file in source tree folder as **".config"** name. 

go to source tree folder to build menuconfig 
<code> make menuconfig </code>

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Make_menuconfig.JPG}}



.config taken from force has features like : 

 - General Setup / Local version string, now it's empty (let it empty ) 

 - General Setup / Preemption model => Fully Preemptible Kernel ( Real-Time ) : this give the rt features. 
       this option is only available after patching with rt56 patch. 

( and of course other features ...) 


{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Menuconfig_generalsetup.JPG}}
{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Menuconfig_Premptionmodel.JPG}}
{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Menuconfig_CheckRTl.JPG}}

       
As we have the kernel configuration, you can see what features are already in the kernel, and whiches are not.
To test kernel viability, i will compile a module which is not there by default , I will do it with "Joystick Interface" :

It's in  : DeviceDrivers >> Input device support >> Joystick Interface

Just put a M like below , then save & Exit menuconfig


{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/JoystickModule.JPG}}


Now when your back in source tree folder type :

<code> make modules_prepare </code>

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/make_module_prepare.JPG}}

Then go to your module folder in source tree. 
For joystick module we've checked in kernel config, it's located in /src/builddemo/linux-5.15/drivers/input 

and launch :

<code> 
syntax is : make -C <path_to_kernel_dir> M=$PWD

so i do : 
~/src/builddemo/linux-5.15/drivers/input$ make -C ~/src/builddemo/linux-5.15/ M=$PWD 

</code>

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Make_module.JPG}}


Make detects that you have checked joystick device as module in kernel config, so it compiles the associated module source file. 


{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/Make_module_2.JPG}}

Then you have your module. 

you can check version in module with command 
<code> grep -a inm joydev.ko </code>

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/grep_inmusic.JPG}}


Now it's time to copy module on your force.


On AKF : 

remount / partition in rw : 

<code> mount remount / -o rw,exec,remount </code> 

copy module file to /usr/lib/modules/5.15.89-inmusic-2023-01-18-rt56/kernel/drivers/input 

Each time i copy a module, i try to respect the source tree path, so if you don't have **drivers/input** folder, create it and put module inside. 
then do command depmod to says system new module is there. 

<code> depmod </code>

Issue command lsmod to see current loaded modules : 

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/lsmod_before.JPG}}

do modprobe joydev 

Issue it again, tadaaaa it's there. 

{{http://dnttalo.cluster029.hosting.ovh.net/Pictures/Kernel/modprobe_joydev.JPG}}