设备树语法
Linux DTS(Device Tree Source)设备树文件后缀为*.dts或*.dtsi，编译后文件为*.dtb。
设备树节点
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[label:] node-name[@unit-address] {
[property-name = value;]
[child nodes];
};
解释：
node-name：节点名; label：节点别名，可选；unit-address：设备地址；
[property-name = value;]是属性键值对；
举例：
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mydemo:demo{
compatible = "demo";
status = "disable";
};
属性重写
经过属性重写后，可以替换同属性的键值对，还可以新增原本没有的属性。重写可以在不同的dtsi文件中。下面例子中就替换了mydemo节点中的status属性。
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//mydemo in xxx1.dtsi
mydemo:demo{
compatible = "demo";
status = "disable";
};
//&mydemo in xxx2.dtsi
&mydemo{
status = "okay";
};
建立简单节点
修改linux-4.14.2_iTop-4412_scp/arch/arm/boot/dts/exynos4412-itop-elite.dts文件，在根节点/{…}内新增如下子节点，注意status属性为”okay”
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mydemo:demo{
compatible = "demo";
status = "okay";
};
编译烧写设备树dtb文件，然后会发现/sys/devices/platform/出现demo设备（前提是设备树节点中状态为okay，而非disable）。
获取设备树节点信息的api
编写最简驱动
demo_drv.c
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#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/of.h>
MODULE_LICENSE("Dual BSD/GPL");
MODULE_AUTHOR("jerry");
#define DRV_NAME "demo"
static int demo_probe(struct platform_device *pdv){
struct device_node *node = pdv->dev.of_node;
struct property *comprop = NULL;
printk(KERN_EMERG "%s ok!\n",__FUNCTION__);
//打印节点信息
printk("node name is %s!\n",node->name);
printk("node fullname is %s!\n",node->full_name);
//查找compatible属性信息
comprop = of_find_property(node,"compatible",NULL);
printk("comprop: %s is %s!\n",comprop->name,(char *)comprop->value);
//查找status属性信息
comprop = of_find_property(node,"status",NULL);
printk("comprop: %s is %s!\n",comprop->name,(char *)comprop->value);
return 0;
}
static int demo_remove(struct platform_device *pdv){
printk(KERN_EMERG "%s ok!\n",__FUNCTION__);
return 0;
}
static const struct of_device_id of_demo_dt_match[] = {
{.compatible = DRV_NAME},
{},
};
MODULE_DEVICE_TABLE(of,of_demo_dt_match);
static struct platform_driver platform_drv_demo = {
.driver = {
.name = DRV_NAME,
.owner = THIS_MODULE,
.of_match_table = of_demo_dt_match,
},
.probe = demo_probe,
.remove = demo_remove,
};
static int __init demo_init(void){
printk(KERN_EMERG "%s ok!\n",__FUNCTION__);
platform_driver_register(&platform_drv_demo);
return 0;
}
static void __exit demo_exit(void){
printk(KERN_EMERG "%s ok!\n",__FUNCTION__);
platform_driver_unregister(&platform_drv_demo);
return;
}
module_init(demo_init);
module_exit(demo_exit);
Makefile：
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#!/bin/bash
export ARCH=arm
obj-m += demo_drv.o
KDIR := /home/jerry/Projects/itop4412_kernel_4_14_2_bsp/linux-4.14.2_iTop-4412_scp/
PWD ?= $(shell pwd)
all:
make -C $(KDIR) M=$(PWD) modules
clean:
rm -rf *.o
交叉编译然后加载到内核后发现probe可以正常执行。
