Write basic driver for BPI R64 ubuntu 18.04 kernel 5.4.0

phthanhdat · April 12, 2021, 5:23pm

i try to write basic driver for BPI-R64 in ubuntu 18.04 kernel 5.4.0: my hello-world-kernel.c : " #include<linux/kernel.h>

#include<linux/init.h>

#include<linux/module.h>

static int hello_init(void)

{

printk(KERN_ALERT "Start successful \n");

return 0;

}

static void hello_exit(void)

{

printk(KERN_ALERT "End successful \n");

}

module_init(hello_init);

module_exit(hello_exit); "

my makefile: " obj-m += hello_kernel_module.o

all:

  make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:

  make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

"

when i run command “make”, it prints “/lib/modules/5.4.0-BPI-R64-Kernel/build No such file or dictionary . Stop” what a surprise, when i do “cd /lib/modules/5.4.0-BPI-R64-Kernel”. it exist “build” dictionary ? what happend ?

[second problem]

i replace “/lib/modules/$(shell uname -r)/build” by “/usr/src/BPI-R64-bsp-5.4_built/linux-mt” in Makefile. it work. i insmod file .ko . it still work. but when i rmmod, console prints modules used.if i used modprobe, console prints no modules found, how to uninstall module ?

DeadMeat · April 13, 2021, 5:13am

It’s the answer to your firs question - /lib/modules/<version>/build - a symlink that should point to sources, you may just replace this symlink with correct one (/usr/src/BPI-R64-bsp-5.4_built/linux-mt).

to use modprobe you should to install this module to /lib/modules. Usually make modules_install. IDK why you cant unload exactly your module, but you can alway use rmmod -f to force.

phthanhdat · April 13, 2021, 5:31am

tks bro. i tried rmmod -f but console prints “function not implemented” . i search gg and resulte is : set CONFIG_MODULE_UNLOAD in kernel . How to set CONFIG_MODULE_UNLOAD = yes in kernel ?

phthanhdat · April 13, 2021, 5:35am

how to install modules to /lib/modules ? copy file .ko to /lib/modules and insmod ?

DeadMeat · April 13, 2021, 6:05am

using make menuconfig (./build.sh config in Frank’s baranch, i don’t have R64, so idk if any scripts are exists in official BSP)
manually edit .config in your src dir (/usr/src/BPI-R64-bsp-5.4_built/linux-mt/.config should work for you)

simple way - copy it to /lib/modules/<ver>/extra (extra is common dir for 3rd party modules, but as i know you can use any). then run depmod and you can use modprobe.

also you can implement the same in your Makefile

I might miss some details, also it’s a general kernel development quietion so you may refer to kernel docs

frank-w · April 13, 2021, 6:23am

Afair build.sh in official repo does not accept params and replace .config via cp with defconfig.

But after starting build.sh there is a menu where you can select change kernel config or similar…then search for the option alex mentioned by pressing / and press 1 to jump to it. Then select it (*) and exit with saving config

Btw do you compile kernel on r64 directly or on host? I guess build-script is only intended for crosscompile (not native on r64)

phthanhdat · April 16, 2021, 3:23pm

i do : bpi-copy file .img to SD card

frank-w · April 16, 2021, 3:58pm

Have you set the option and do you see your module as .ko file?

Kernel is no img file…it is uImage dtb and modules (ko files +some other files)

phthanhdat · April 17, 2021, 4:19am

your mean is : Module.symvers, modules.builtin,modules.builtin.modinfo,modules.order,System.map,vmlinux ,vmlinux.o ?

phthanhdat · April 17, 2021, 4:24am

i run ./build.sh and press 4 for modified, save and load. then i still run ./build.sh and press 3 for Build kernel only. after 15 minutes, it prints Build success! . i check current folder, i dont see new file . i check folder linux-mt and see a list : modules.builtin,modules.builtin.modinfo,modules.order,System.map,vmlinux ,vmlinux.o .

frank-w · April 17, 2021, 7:43am

Idk how the official kernel was installed. But you can try my debian-image with my kernel-repo (module_remove already active). My build.sh asks for installing to sdcard after build…only need to adjust uenv.txt after install

phthanhdat · April 17, 2021, 7:48am

ok, tks u. i have 1 question. after i choose 1 (run ./build.sh), i have folder SD. how to create file .img(i use bpi-copy tools to SDCard) or how write to SDCard?

frank-w · April 17, 2021, 8:02am

Build.sh from my kernel-repo? 1 is pack there…you have to use 2=install

phthanhdat · April 17, 2021, 8:04am

from source : https://github.com/BPI-SINOVOIP/BPI-R64-bsp-5.4

what do u mean ?

frank-w · April 17, 2021, 8:07am

Ok,you still use official kernel-repo…there i do not know how to install

I guess it’s legacy boot,so you need uImage and dtb on BPI-BOOT partition and your modules (with additional files) in BPI-ROOT/lib/modules/kernelname/

Afair there was a uenv.txt too if filename of uImage or dtb is different

phthanhdat · April 17, 2021, 8:08am

tks u so much . have good a day bro

frank-w · April 17, 2021, 9:11am

Seems like option 1 creates tgz files which needs to be unpacked to sdcard (like my option 1,but here multiple)

github.com

BPI-SINOVOIP/BPI-R64-bsp-5.4/blob/master/build.sh#L58


	## copy files to BPI-ROOT
	#
	mkdir -p $R/usr/lib/u-boot/bananapi/${board}
	cp -a $U/*.gz $R/usr/lib/u-boot/bananapi/${board}/
	rm -rf $R/lib/modules
	mkdir -p $R/lib/modules
	cp -a $T/${BPILINUX}/output/lib/modules/${kernel} $R/lib/modules
	#
	## create files for bpi-tools & bpi-migrate
	#
	(cd $B ; tar czvf $SD/BPI-BOOT-${board}-${service}.tgz .)
	(cd $R ; tar czvf $SD/${kernel}-net.tgz lib/modules/${kernel}/kernel/net)
	(cd $R ; mv lib/modules/${kernel}/kernel/net $R/net)
	(cd $R ; tar czvf $SD/${kernel}.tgz lib/modules)
	(cd $R ; mv $R/net lib/modules/${kernel}/kernel/net)
	(cd $R ; tar czvf $SD/BOOTLOADER-${board}-${service}.tgz usr/lib/u-boot/bananapi)


	return #SKIP
}


list_boards() {

Comment states that you can install it via bpi-tools

Afaik you need to unpack

$SD/BPI-BOOT-${board}-${service}.tgz to BPI-BOOT
$SD/${kernel}.tgz to BPI-ROOT

btw. tried your code and compiled in my tree…at least “MODULE_LICENSE(“GPL”);” was missing

diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index bd1c444e1170..8640523fcb13 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -57,3 +57,5 @@ obj-$(CONFIG_UACCE)           += uacce/
 obj-$(CONFIG_XILINX_SDFEC)     += xilinx_sdfec.o
 obj-$(CONFIG_HISI_HIKEY_USB)   += hisi_hikey_usb.o
 obj-$(CONFIG_MTK_COMBO)        += mediatek/
+
+obj-m+= mydriver.o
diff --git a/drivers/misc/mydriver.c b/drivers/misc/mydriver.c
new file mode 100644
index 000000000000..31e98f8eebd6
--- /dev/null
+++ b/drivers/misc/mydriver.c
@@ -0,0 +1,19 @@
+#include<linux/kernel.h>
+#include<linux/init.h>
+#include<linux/module.h>
+
+static int hello_init(void)
+{
+       printk(KERN_ALERT "Start successful \n");
+       return 0;
+}
+
+static void hello_exit(void)
+{
+       printk(KERN_ALERT "End successful \n");
+}
+
+module_init(hello_init);
+module_exit(hello_exit);
+
+MODULE_LICENSE("GPL");

i used makefile from drivers/misc to place my module there.

https://tldp.org/LDP/lkmpg/2.6/html/x279.html shows __init and __exit statements…imho they are for reducing memory consumption.btw. there is a nice tutorial here

tried to load it:

root@bpi-r2:~# modprobe mydriver                                                                                                     
[  112.868991] Start successful                                                                                                      
root@bpi-r2:~# modprobe -r mydriver                                                                                                  
[  116.607067] End successful                                                                                                        
root@bpi-r2:~#