设备总线驱动模型：http://blog.csdn.net/lizuobin2/article/details/51570196
本文主要参考：http://www.wowotech.net/device_model/platform_device.html
platform平台设备驱动是基于设备总线驱动模型的，它只不过是将 device 进一步封装成为 platform_device，将 device_driver 进一步封装成为 platform_device_driver,前面已经分析过设备总线驱动模型，关于device 与 device_driver 的注册过程以及它们在sysfs文件系统中的层次关系就不在分析，本文重点分析platform平台设备驱动与设备总线驱动模型相比较新增添的那些东西。
在Linux设备模型的抽象中，存在着一类称作“Platform Device”的设备，内核是这样描述它们的（Documentation/driver-model/platform.txt）：
Platform devices are devices that typically appear as autonomous entities in the system. This includes legacy port-based devices and host bridges to peripheral buses, and most controllers integrated into system-on-chip platforms. What they usually have
in common is direct addressing from a CPU bus. Rarely, a platform_device will be connected through a segment of some other kind of bus; but its registers will still be directly addressable.
概括来说，Platform设备包括：基于端口的设备（已不推荐使用，保留下来只为兼容旧设备，legacy）；连接物理总线的桥设备；集成在SOC平台上面的控制器；连接在其它bus上的设备（很少见）。等等。
这些设备有一个基本的特征：可以通过CPU bus直接寻址（例如在嵌入式系统常见的“寄存器”）。因此，由于这个共性，内核在设备模型的基础上（device和device_driver），对这些设备进行了更进一步的封装，抽象出paltform bus、platform device和platform driver，以便驱动开发人员可以方便的开发这类设备的驱动。
可以说，paltform设备对Linux驱动工程师是非常重要的，因为我们编写的大多数设备驱动，都是为了驱动plaftom设备。
platform_bus_type
我们知道，在设备总线驱动模型的中，BUS像一个月老一样，通过它的match函数，将注册到bus中的device与driver进行配对，那么每一个不同的bus 都有自己的match函数，我们来看看platform_bus_type.
struct bus_type platform_bus_type = {
.name = "platform",
.dev_attrs = platform_dev_attrs,
.match = platform_match,
.uevent = platform_uevent,
.pm = &platform_dev_pm_ops,
};
static int platform_match(struct device *dev, struct device_driver *drv)
{
struct platform_device *pdev = to_platform_device(dev);
struct platform_driver *pdrv = to_platform_driver(drv);
/* match against the id table first */
if (pdrv->id_table)
return platform_match_id(pdrv->id_table, pdev) != NULL;
/* fall-back to driver name match */
return (strcmp(pdev->name, drv->name) == 0);
}
如果platform_device_driver中定义了id_table，则调用 platform_match_id 进行匹配struct platform_device {
const char * name;
int id;
struct device dev;
u32 num_resources;
struct resource * resource;
struct platform_device_id *id_entry;
/* arch specific additions */
struct pdev_archdata archdata;
}; name，设备的名称，该名称在设备注册时，会拷贝到dev.init_name中。struct resource {
resource_size_t start;
resource_size_t end;
const char *name;
unsigned long flags;
struct resource *parent, *sibling, *child;
};static struct resource led_resource[] = { //jz2440的参数，驱动未测试
[0] = {
.start = 0x56000010,
.end = 0x56000010 + 8 - 1,
.flags = IORESOURCE_MEM,
},
[1] = {
.start = 5,
.end = 5,
.flags = IORESOURCE_IRQ,
},
};
static struct platform_device led_dev = {
.name = "myled", //设备名字 与 驱动相匹配
.id = -1,
.num_resources = ARRAY_SIZE(led_resource),
.resource = led_resource,
.dev = {
.release = led_release,
//.devt = MKDEV(252, 1),
},
};
struct platform_driver {
int (*probe)(struct platform_device *);
int (*remove)(struct platform_device *);
void (*shutdown)(struct platform_device *);
int (*suspend)(struct platform_device *, pm_message_t state);
int (*resume)(struct platform_device *);
struct device_driver driver;
struct platform_device_id *id_table;
};int platform_driver_register(struct platform_driver *drv)
{
drv->driver.bus = &platform_bus_type;
if (drv->probe)
drv->driver.probe = platform_drv_probe;
if (drv->remove)
drv->driver.remove = platform_drv_remove;
if (drv->shutdown)
drv->driver.shutdown = platform_drv_shutdown;
return driver_register(&drv->driver);
} struct platform_driver结构和struct device_driver非常类似,上边的platform_drv_probe、platform_drv_remove、platform_drv_shutdown，只不过稍作转换调用platform_driver中的probe、remove、shutdown函数，举个例子稍微看一下
static int platform_drv_probe(struct device *_dev)
{
struct platform_driver *drv = to_platform_driver(_dev->driver);
struct platform_device *dev = to_platform_device(_dev);
return drv->probe(dev);
}
/* include/linux/platform_device.h */
extern int platform_device_register(struct platform_device *);
extern void platform_device_unregister(struct platform_device *);
extern void arch_setup_pdev_archdata(struct platform_device *);
extern struct resource *platform_get_resource(struct platform_device *, unsigned int, unsigned int);
extern int platform_get_irq(struct platform_device *, unsigned int);
extern struct resource *platform_get_resource_byname(struct platform_device *, unsigned int, const char *);
extern int platform_get_irq_byname(struct platform_device *, const char *);
extern int platform_add_devices(struct platform_device **, int);
extern struct platform_device *platform_device_register_full(const struct platform_device_info *pdevinfo);
static inline struct platform_device *platform_device_register_resndata(
struct device *parent, const char *name, int id,
const struct resource *res, unsigned int num,
const void *data, size_t size)
static inline struct platform_device *platform_device_register_simple(
const char *name, int id,
const struct resource *res, unsigned int num)
static inline struct platform_device *platform_device_register_data(
struct device *parent, const char *name, int id,
const void *data, size_t size)
extern struct platform_device *platform_device_alloc(const char *name, int id);
extern int platform_device_add_resources(struct platform_device *pdev,
const struct resource *res,
unsigned int num);
extern int platform_device_add_data(struct platform_device *pdev,
const void *data, size_t size);
extern int platform_device_add(struct platform_device *pdev);
extern void platform_device_del(struct platform_device *pdev);
extern void platform_device_put(struct platform_device *pdev); platform_device_register、platform_device_unregister，Platform设备的注册/注销接口，和底层的device_register等接口类似。 extern struct platform_device *platform_create_bundle(
struct platform_driver *driver, int (*probe)(struct platform_device *),
struct resource *res, unsigned int n_res,
const void *data, size_t size); 只要提供一个platform_driver（要把driver的probe接口显式的传入），并告知该设备占用的资源信息，platform模块就会帮忙分配资源，并执行probe操作。对于那些不需要热拔插的设备来说，这种方式是最省事的了。
简单一例：
开发板：Mini2440
内核版本：2.6.32.2
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <linux/input.h>
#include <linux/platform_device.h>
// 设备资源
static struct resource led_resource[] = { //jz2440的参数，驱动未测试
[0] = {
.start = 0x56000010,
.end = 0x56000010 + 8 - 1,
.flags = IORESOURCE_MEM,
},
[1] = {
.start = 5,
.end = 5,
.flags = IORESOURCE_IRQ,
},
};
static void led_release(struct device *dev){
}
// 创建一个设备
static struct platform_device led_dev = {
.name = "myled", //设备名字 与 驱动相匹配
.id = -1,
.num_resources = ARRAY_SIZE(led_resource),
.resource = led_resource,
.dev = {
.release = led_release,
//.devt = MKDEV(252, 1),
},
};
static int led_dev_init(void){
//向bus注册led_dev match drv链表进行配对
platform_device_register(&led_dev);
return 0;
}
static void led_dev_exit(void){
platform_device_unregister(&led_dev);
}
module_init(led_dev_init);
module_exit(led_dev_exit);
MODULE_LICENSE("GPL");
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/device.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/irq.h>
#include <asm/uaccess.h>
#include <linux/platform_device.h>
#include <linux/io.h>
static int major;
static struct class *cls;
static struct device *dev;
static volatile unsigned long *gpio_con;
static volatile unsigned long *gpio_dat;
static int pin;
static int led_open(struct inode *inode, struct file *file){
*gpio_con &= ~(0x03 << (pin*2));
*gpio_con |= (0x01 << (pin*2));
return 0;
}
static ssize_t led_write(struct file *file, const char __user *buf,
size_t count, loff_t *ppos){
int val;
copy_from_user(&val, buf, count);
if(val == 1){
*gpio_dat &= ~(1<<pin);
}else{
*gpio_dat &= (1<<pin);
}
return 0;
}
static struct file_operations led_fops = {
.owner = THIS_MODULE,
.open = led_open,
.write = led_write,
};
static int led_probe(struct platform_device *pdev){
struct resource *res;
// 最后一个参数 0 表示第1个该类型的资源
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
gpio_con = ioremap(res->start, res->end - res->start + 1);
gpio_dat = gpio_con + 1;
res = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
pin = res->start;
printk("led_probe, found led\n");
// 注册设备驱动 创建设备节点
major = register_chrdev(0, "myled", &led_fops);
// 创建类
cls = class_create(THIS_MODULE, "myled");
// 创建设备节点
dev = device_create(cls, NULL, MKDEV(major, 0), NULL, "led");
return 0;
}
static int led_remove(struct platform_device *pdev){
printk("led_remove, remove led\n");
// 删除设备节点
device_unregister(dev);
// 销毁类
class_destroy(cls);
// 取消注册设备驱动
unregister_chrdev(major, "myled");
// 取消内存映射
iounmap(gpio_con);
return 0;
}
struct platform_driver led_drv = {
.probe = led_probe, //匹配到dev之后调用probe
.remove = led_remove,
.driver = {
.name = "myled",
},
};
static int led_drv_init(void){
platform_driver_register(&led_drv);
return 0;
}
static void led_drv_exit(void){
platform_driver_unregister(&led_drv);
}
module_init(led_drv_init);
module_exit(led_drv_exit);
MODULE_LICENSE("GPL");
原文：http://blog.csdn.net/lizuobin2/article/details/51607813