Android平台驱动模块编写实例

       Android平台的驱动编译跟普通的linux驱动编写有一点区别，主要区别在Makefile文件(需要交叉工具连DBG_CROSS_COMPILE)),这里以hello.c文件为例

#include <linux/module.h>

static int __init hello_init(void)
{ 
	printk(KERN_INFO "%s\n",__FUNCTION__);      
	return 0;
}

static void __exit hello_exit(void)
{	
	printk(KERN_INFO "%s\n",__FUNCTION__);
}

module_init(hello_init);
module_exit(hello_exit);
MODULE_LICENSE("GPL");

如果是普通的linux驱动，Makefile的写法为

ifeq ($(KERNELRELEASE),)
KERNELDIR ?= /usr/src/linux-headers-4.4.0-24-generic/  
PWD :=$(shell pwd)

modules:  
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules  
modules_install:  
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install  
clean:  
	rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules.order  Module.symvers  
.PHONY: modules modules_install clean  
else  
	obj-m:= hello.o  
endif

对于Android平台，Makefile的内容为

ifeq ($(KERNELRELEASE),)  
  
KERNELDIR_OUT ?= Android源码路径/kernel
CROSS_COMPILE ?= Android源码路径/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/bin/arm-eabi-
PWD :=$(shell pwd)  
  
modules:  
	$(MAKE) -C $(KERNELDIR_OUT) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) modules 
modules_install:  
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install  
clean:  
	rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules.order  Module.symvers 
.PHONY: modules modules_install clean  
else  
	obj-m:= hello.o  
endif

        对于某些平台(qcom或者mtk)，所有的生成文件都放在了Android源码的out目录下，所有内核源码路径要改成( Android源码根路径/out/target/product/具体cpu/obj/KERNEL_OBJ)，对于64系统，要将ARCH=arm改成ARCH=arm64。其实，路径具体怎么填，参考编译源码时的打印信息即可，如

make -C kernel-3.18 O=/Android源码根路径/out/target/product/xxxx/obj/KERNEL_OBJ 
ARCH=arm64 CROSS_COMPILE=/Android源码根路径/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/bin/aarch64-linux-android- 
ROOTDIR=/home/w/xxx  modules

如果驱动模块由多个c文件组成，Makefile的编写如下

ifeq ($(KERNELRELEASE),)         
KERNELDIR_OUT ?= /home/w/M8974AAAAANLYD4275/out/target/product/msm8974/obj/KERNEL_OBJ
CROSS_COMPILE ?= /home/w/M8974AAAAANLYD4275/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/bin/arm-eabi-    
PWD := $(shell pwd)             
modules:                         #编译为驱动模块    
    $(MAKE) -C $(KERNELDIR_OUT) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) modules    
modules_install:    
    $(MAKE) -C $(KERNELDIR_OUT) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) modules  
clean:    
    rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules.order Module.symvers        
.PHONY: modules modules_install clean         
else                                  
GT9xx_CORE_OBJS  := gt9xx.o             #指定驱动模块的核心文件（有init 和 exit）    
GT9xx_OTHER_OBJS := goodix_tool.o gt9xx_update.o #依赖文件    
touchscreen-objs   := $(GT9xx_CORE_OBJS) $(GT9xx_OTHER_OBJS) #xxx-objs := 指定驱动模块的所有依赖文件    
obj-m := touchscreen.o   #最终由xxx-objs链接生成touchscreen.o，再生成touchscreen.ko    
endif

如果要多个c文件分别编译成相应的驱动，Makefile的编写如下

ifeq ($(KERNELRELEASE),)    
KERNELDIR_OUT ?= /home/w/M8974AAAAANLYD4275/out/target/product/msm8974/obj/KERNEL_OBJ  
CROSS_COMPILE ?= /home/w/M8974AAAAANLYD4275/prebuilts/gcc/linux-x86/arm/arm-eabi-4.8/bin/arm-eabi-  
PWD :=$(shell pwd)  
modules:  
	$(MAKE) -C $(KERNELDIR_OUT) M=$(PWD) ARCH=arm CROSS_COMPILE=$(CROSS_COMPILE) modules  
modules_install:  
	$(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install  
clean:  
	rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions modules.order  Module.symvers app  
.PHONY: modules modules_install clean  
else  
    obj-m+= notifier_chain.o  
    obj-m+= consumer.o  
    obj-m+= producer.o  
endif