Linux driver easy to learn notes

PC operating system: Ubuntu 16.04 LTS
Compiler: arm poky Linux gnueabi GCC 4.9.1

Based on the i.mx6 platform, the Linux driver module has been modified for some time, in which a lot of information is checked intermittently, and it feels that the knowledge is not so coherent, so it's time to start from the foundation.

1, Create a minimum driver module template

Create a hello.c file

#include<linux/init.h> #include<linux/module.h> /*************************************************************************************************/ // Local macro definition /*************************************************************************************************/ #define EN_DEBUG 1 /* Debug information switch */ #if EN_DEBUG #define PRINT(x...) printk(KERN_EMERG x) /* Improve printing level */ #else #define PRINT(x...) #endif /************************************************************************************************** ** Function name: DRV init ** Function: Driver initialization function, called at load time ** Parameter: None ** Return: no **************************************************************************************************/ static int __init drv_init(void) { PRINT("%s ------ \n", __FUNCTION__); return 0; } /************************************************************************************************** ** Function name: drv_exit ** Function Description: i2c driver exit function, called when uninstalling ** Parameter: None ** Return: no **************************************************************************************************/ static void __exit drv_exit(void) { PRINT("%s ------ \n", __FUNCTION__); } module_init(drv_init); /* Module initialization */ module_exit(drv_exit); /* Module unloading */ MODULE_AUTHOR("hrx"); /* Module author */ MODULE_DESCRIPTION("Linux Driver"); /* Module description */ MODULE_VERSION("1.0.0"); /* Module version */ MODULE_LICENSE("GPL"); /* License that the module complies with */

• Loading function
• Unloading function
• Author, description, version, permission, etc
• Print debug information (printk)

• The user layer uses the printf function
• Linux kernel layer uses the print function
• The Kern? Emerg macro in the print is to set the output level (this is the output level that can output debugging information directly). More definitions can be seen in the kernel \ include \ Linux \ Kern? Levels. H file.
• If the print level is not high, you can also output the cached print information through the dmesg -c command (- c is to clear the cache after output).

2, Write Makefile

#Current directory path PWD = $(shell pwd) #Linux kernel root path KERNEL_DIR = $(PWD)/../../kernel #Driver name DRVNAME = hello #The obj-m option will be compiled as a module and will not be compiled into the kernel. Instead, it will generate a. ko file independently #The obj-y option is compiled into the kernel obj-m += hello.o build: $(MAKE) -C $(KERNEL_DIR) M=$(PWD) clean: @rm -rf *.o *.ko .*.cmd *.mod.c *.order *.symvers .tmp_versions *~

• Kernel? Dir is the kernel directory path relative to the current Makefile.
• **$(MAKE) * * is the macro definition of the make command, which may contain other parameters (I'm here only MAKE).
• -C this C is uppercase. It is to switch to the kernel? Dir directory and make again.
• **M = * * is the directory where the Linux driver source code is specified.

3, Generate driver files (*. ko)

Because I use it on the development board, I need to cross compile.
Reference resources: Configuring the imx6 cross compiling environment

Execute the make command to generate the. ko file.

make build

4, Loading and unloading drive

First, you need to transfer hello.ko to the development board to perform subsequent operations.

root@imx6qsabresd:/tmp# insmod hello.ko [ 7707.518557] drv_init ------

This outputs the initialization function.

root@imx6qsabresd:/tmp# rmmod hello.ko [ 7843.203066] drv_exit ------

This outputs the exit function.

5, View driver information

root@imx6qsabresd:/tmp# lsmod Tainted: G hello 832 0 - Live 0x7f057000 (O)

lsmod actually reads the contents of * * / proc/modules * * file

root@imx6qsabresd:/tmp# cat /proc/modules hello 832 0 - Live 0x7f057000 (O)

After the driver is loaded, a folder with the same name as the driver file will be generated in / sys/module / directory, where the driver loading information is stored.

root@imx6qsabresd:/tmp# ls -l /sys/module/hello/ -r--r--r-- 1 root root 4096 Nov 10 19:40 coresize drwxr-xr-x 2 root root 0 Nov 10 19:40 holders -r--r--r-- 1 root root 4096 Nov 10 19:40 initsize -r--r--r-- 1 root root 4096 Nov 10 19:40 initstate drwxr-xr-x 2 root root 0 Nov 10 19:40 notes -r--r--r-- 1 root root 4096 Nov 10 19:40 refcnt drwxr-xr-x 2 root root 0 Nov 10 19:40 sections -r--r--r-- 1 root root 4096 Nov 10 19:40 srcversion -r--r--r-- 1 root root 4096 Nov 10 19:40 taint --w------- 1 root root 4096 Nov 10 19:35 uevent

• This command queries the driver file directly, and does not need to be loaded.
• The development board is castrated with this command, which is the driver file information viewed on the PC.
• The author, description, version, permission and other descriptions defined in the driver file can be found.

hrx@@@:~/Imx6/platform/driver/hello$ modinfo hello.ko filename: /home/hrx/Imx6/platform/driver/hello/hello.ko license: GPL version: 1.0.0 description: Linux Driver author: hrx srcversion: A5F2F4E32D4DF79D5CF15B7 depends: vermagic: 3.14.38-6UL_ga-svn12810 SMP preempt mod_unload modversions ARMv7 p2v8

Reference 1: https://blog.csdn.net/leon1741/article/details/78165507

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11 February 2020, 05:10 | Views: 6965