Linux设备模型（下）之Platform
从Linux2.6内核起，引入一套新的驱动管理和注册机制：platform_device和 platform_driver 。Linux 中大部分的设备驱动，都可以使用这套机制，设备用 platform_device 表示；驱动用platform_driver 进行注册。 platform是一个虚拟的地址总线，相比pci，usb，它主要用于描述SOC上的片上资源，比如s3c2440上集成的控制器（lcd，watchdog，rtc等）， platform所描述的资源有一个共同点，就是在cpu的总线上直接取址。平台设备会分到一个名称(用在驱动绑定中)以及一系列诸如地址和中断请求号(IRQ)之类的资源.
struct platform_device {
const char * name;
intid;
struct device dev;
u32num_resources;
struct resource * resource;
};
平台驱动遵循标准驱动模型的规范, 平台驱动按标准规范对电源管理和关机通告提供支 持
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 (*suspend_late)(struct platform_device *, pm_message_t state);
int (*resume_early)(struct platform_device *);
int (*resume)(struct platform_device *);
struct device_driver driver;
};
probe()总应该核实指定的设备硬件确实存在;平台设置代码有时不能确定这一点
系统为platform总线定义一个bus_type的实例platform_bus_type，通过其成员函数match()，确定device和driver如何匹配。
匹配platform_device和platform_driver主要看二者的name字段是否相同。（name必须要相同才能匹配）
用platform_device_register(platform_device*)函数注册单个的平台设备。
一般是在平台的BSP文件中定义platform_device，通过platform_add_devices(platform_device*)函数将平台设备注册到系统中platform_driver 的注册与注销：
platform_driver_register(platform_driver*)
platform_driver_unregister(platform_driver*)
设备资源（struct resource)
关于资源的操作（平台设备会分到一系列诸如地址和中断请求号(IRQ)之类的资源)
struct resource {
resource_size_t start;
resource_size_t end;
const char *name;
unsigned long flags;
// IORESOURCE_IO
//IORESOURCE_MEM
//IORESOURCE_IRQ
//IORESOURCE_DMA
struct resource *parent, *sibling, *child;
};
基于资源的分类（flags）有I/O端口、IRQ、DMA等等，而I/O端口又分为2种类型，IORESOURCE_IO（I/O映射） IORESOURCE_MEM（内存映射）CPU对外设IO端口物理地址的编址方式有2种：一种是IO映射方式（IO-mapped）， 另一种是内存映射方式（Memory-mapped）。具体采用哪一种方式则取决于CPU的体系结构。 像X86体系对外设就专门实现了一个单独地址空间，并且有专门的I/O指令来访问I/O端口，像ARM体系结构通常只是实现一个物理地址空间，I/O端口就被映射到CPU的单一物理地址空间中，而成为内存的一部分，所以一般资源都采用（IORESOURCE_MEM）。linux中对设备的资源按照资源树的结构来组织(其实就是一个链表结构的插入、删除、查找等操作），上面再添加设备（platform_device_add）的同时对相应的资源在资源树上进行插入操作
int insert_resource(struct resource *parent, struct resource *new)
关于platform resource有相关的函数进行对资源的操作。
struct resource *platform_get_resource(struct platform_device *, unsigned int, unsigned int);
int platform_get_irq(struct platform_device *, unsigned int);
struct resource *platform_get_resource_byname(struct platform_device *, unsigned int, char *);
int platform_get_irq_byname(struct platform_device *, char *);
例如s3c2440的watchdog资源分配实例：
watchdog寄存器的基地址为0x5300000
#define S3C2410_PA_WATCHDOG (0x53000000)
#define S3C24XX_SZ_WATCHDOG SZ_1M
static struct resource s3c_wdt_resource[] = {
[0] = {
.start = S3C24XX_PA_WATCHDOG,
.end = S3C24XX_PA_WATCHDOG + S3C24XX_SZ_WATCHDOG - 1,
.flags = IORESOURCE_MEM, //内存映射
},
[1] = {
.start = IRQ_WDT,
.end = IRQ_WDT,
.flags = IORESOURCE_IRQ, //IRQ
}
};
plat_button_device.c：
#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <mach/regs-gpio.h>
#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/io.h>
/*平台资源的定义*/
static struct resource s3c_buttons_resource[] = {
[0]={
.start = S3C24XX_PA_GPIO,// (0x56000000)
.end = S3C24XX_PA_GPIO + S3C24XX_SZ_GPIO - 1,//(0x56000000) + 0x00100000 -1
.flags = IORESOURCE_MEM,
},
[1]={
.start = IRQ_EINT7,
.end = IRQ_EINT7,
.flags = IORESOURCE_IRQ,
},
[2]={
.start = IRQ_EINT1,
.end = IRQ_EINT1,
.flags = IORESOURCE_IRQ,
},
[3]={
.start = IRQ_EINT2,
.end = IRQ_EINT2,
.flags = IORESOURCE_IRQ,
},
[4]={
.start = IRQ_EINT3,
.end = IRQ_EINT3,
.flags = IORESOURCE_IRQ,
},
[5]={
.start = IRQ_EINT4,
.end = IRQ_EINT4,
.flags = IORESOURCE_IRQ,
},
[6]={
.start = IRQ_EINT5,
.end = IRQ_EINT5,
.flags = IORESOURCE_IRQ,
}
};
static struct platform_device *s3c_buttons;
static int __init platform_init(void)
{
s3c_buttons = platform_device_alloc("gec2440-buttons",-1);
platform_device_add_resources(s3c_buttons,&s3c_buttons_resource,7);
/*平台设备的注册*/
platform_device_add(s3c_buttons);
}
static void __exit platform_exit(void)
{
platform_device_unregister(s3c_buttons);
}
module_init(platform_init);
module_exit(platform_exit);
MODULE_AUTHOR("Steven Bai");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:gec2440buttons");
plat_button_driver.c：
#include <linux/module.h>
#include <linux/types.h>
#include <linux/miscdevice.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/platform_device.h>
#include <linux/interrupt.h>
#include <linux/clk.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <mach/map.h>
#include <mach/regs-gpio.h>
#include <linux/poll.h>
#include <linux/irq.h>
#include <asm/unistd.h>
#include <linux/device.h>
#define DEVICE_NAME "buttons"
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
static volatile int ev_press = 0;
static int key_value;
static struct device *buttons_dev; /* platform device attached to */
static struct resource *buttons_mem;
static struct resource *buttons_irq;
static void __iomem *buttons_base;
static int button_irqs[6];
static irqreturn_t buttons_interrupt(int irq, void *dev_id)
{
int i;
for(i=0; i<6; i++){
if(irq == button_irqs[i]){
printk("==>interrput number:%d\n",irq);
key_value = i;
ev_press =1;
wake_up_interruptible(&button_waitq);
}
}
return IRQ_RETVAL(IRQ_HANDLED);
}
static int s3c24xx_buttons_open(struct inode *inode, struct file *file)
{
int i;
int err = 0;
/*注册中断*/
for(i=0; i<6; i++){
if (button_irqs[i] < 0)
continue;
/*中断触发方式：上升沿触发*/
err = request_irq(button_irqs[i],buttons_interrupt,IRQ_TYPE_EDGE_RISING,NULL,NULL);
if(err)
break;
}
if (err) {
i--;
for (; i >= 0; i--) {
if (button_irqs[i] < 0) {
continue;
}
disable_irq(button_irqs[i]);
free_irq(button_irqs[i], NULL);
}
return -EBUSY;
}
ev_press = 0;
return 0;
}
static int s3c24xx_buttons_close(struct inode *inode, struct file *file)
{
int i;
for (i=0; i<6; i++) {
if (button_irqs[i] < 0) {
continue;
}
free_irq(button_irqs[i],NULL);
}
return 0;
}
static int s3c24xx_buttons_read(struct file *filp, char __user *buff, size_t count, loff_t *offp)
{
unsigned long err;
if (!ev_press) {
if (filp->f_flags & O_NONBLOCK)
return -EAGAIN;
else
wait_event_interruptible(button_waitq, ev_press);
}
ev_press = 0;
err = copy_to_user(buff, &key_value, sizeof(key_value));
return sizeof(key_value);
}
static unsigned int s3c24xx_buttons_poll( struct file *file, struct poll_table_struct *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait);
if (ev_press){
mask |= POLLIN | POLLRDNORM;
}
return mask;
}
static struct file_operations gec2440buttons_fops = {
.owner = THIS_MODULE,
.open = s3c24xx_buttons_open,
.release = s3c24xx_buttons_close,
.read = s3c24xx_buttons_read,
.poll = s3c24xx_buttons_poll,
};
static struct miscdevice gec2440_miscdev = {
.minor = MISC_DYNAMIC_MINOR,
.name = DEVICE_NAME,
.fops = &gec2440buttons_fops,
};
/* device interface */
static int gec2440_buttons_probe(struct platform_device *pdev)
{
struct resource *res;
struct device *dev;
int ret;
int size;
int i;
printk("probe:%s\n", __func__);
dev = &pdev->dev;
buttons_dev = &pdev->dev;
/*平台资源获取*/
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
dev_err(dev, "no memory resource specified\n");
return -ENOENT;
}
size = (res->end - res->start) + 1;
buttons_mem = request_mem_region(res->start, size, pdev->name);
if (buttons_mem == NULL) {
dev_err(dev, "failed to get memory region\n");
ret = -ENOENT;
goto err_req;
}
buttons_base = ioremap(res->start, size);
if (buttons_base == NULL) {
dev_err(dev, "failed to ioremap() region\n");
ret = -EINVAL;
goto err_req;
}
printk(KERN_DEBUG"probe: mapped buttons_base=%p\n", buttons_base);
/*get irq number*/
for(i=0; i<6; i++)
{
buttons_irq = platform_get_resource(pdev,IORESOURCE_IRQ,i);
if(buttons_irq == NULL)
{
dev_err(dev,"no irq resource specified\n");
ret = -ENOENT;
goto err_map;
}
button_irqs[i] = buttons_irq->start;
printk("button_irqs[%d]=%d\n",i,button_irqs[i]);
}
ret = misc_register(&gec2440_miscdev);
return 0;
err_map:
iounmap(buttons_base);
err_req:
release_resource(buttons_mem);
kfree(buttons_mem);
return ret;
}
static int gec2440_buttons_remove(struct platform_device *dev)
{
release_resource(buttons_mem);
kfree(buttons_mem);
buttons_mem = NULL;
iounmap(buttons_base);
misc_deregister(&gec2440_miscdev);
return 0;
}
/*平台驱动定义*/
static struct platform_driver gec2440buttons_driver = {
.probe = gec2440_buttons_probe,
.remove = gec2440_buttons_remove,
.driver = {
.owner = THIS_MODULE,
.name = "gec2440-buttons",
},
};
static char banner[] __initdata =
"gec2440 Buttons Driver\n";
static int __init buttons_init(void)
{
printk(banner);
/*平台驱动注册*/
platform_driver_register(&gec2440buttons_driver);
return 0;
}
static void __exit buttons_exit(void)
{
platform_driver_unregister(&gec2440buttons_driver);
}
module_init(buttons_init);
module_exit(buttons_exit);
MODULE_AUTHOR("Steven Bai");
MODULE_DESCRIPTION("gec2440 Buttons Driver");
MODULE_LICENSE("GPL");
开发板一上电后，可以/sys/bus/platform/下会挂上这个设备和对应的驱动