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.
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- struct bus_type platform_bus_type = {
- .name = "platform",
- .dev_attrs = platform_dev_attrs,
- .match = platform_match,
- .uevent = platform_uevent,
- .pm = &platform_dev_pm_ops,
- };
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- 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
举个例子:
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- static struct platform_device_id s3c24xx_driver_ids[] = {
- {
- .name = "s3c2410-i2c",
- .driver_data = TYPE_S3C2410,
- }, {
- .name = "s3c2440-i2c",
- .driver_data = TYPE_S3C2440,
- }, { },
- };
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- struct platform_device s3c_device_i2c0 = {
- .name = "s3c2410-i2c",
- #ifdef CONFIG_S3C_DEV_I2C1
- .id = 0,
- #else
- .id = -1,
- #endif
- .num_resources = ARRAY_SIZE(s3c_i2c_resource),
- .resource = s3c_i2c_resource,
- };
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- static const struct platform_device_id *platform_match_id(struct platform_device_id *id, struct platform_device *pdev)
- {
- while (id->name[0]) {
- if (strcmp(pdev->name, id->name) == 0) {
- pdev->id_entry = id;
- return id;
- }
- id++;
- }
- return NULL;
- }
显然,platform_match_id
的作用就是遍历整个 Id_table 数组,寻找是否有与 platform_device->name 同名的,如果有,则返回这个 Platform_device_id ,使用Id_table 打破了原本设备总线驱动模型,一个 device 只能用与一个 device_driver 配对的局限性。现在一个platform_device_driver 可以与多个platform_device配对。
如果没有,则只是根据 platform_device_driver->name 与 platform_device->name 进行比较,这也就是老师为啥在写平台设备驱动程序的时候经常说,“将驱动注册到内核中去,如果有同名设备,则调用driver->probe函数....”。
pletform_device 中的 id 的作用:
if (pdev->id != -1) /* 如果不是-1 对name编号 */
dev_set_name(&pdev->dev, "%s.%d", pdev->name, pdev->id);
else /* -1时直接是名字 */
dev_set_name(&pdev->dev, pdev->name);
从device封装而来的platform_device
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- 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。
dev,真正的设备,通过 container_of ,就能找到整个platform_device ,访问其它成员,如后面要提到的 resource
num_resources、resource,该设备的资源描述,由struct resource(include/linux/ioport.h)结构抽象。
在Linux中,系统资源包括I/O、Memory、Register、IRQ、DMA、Bus等多种类型。这些资源大多具有独占性,不允许多个设备同时使用,因此Linux内核提供了一些API,用于分配、管理这些资源。
当某个设备需要使用某些资源时,只需利用struct
resource组织这些资源(如名称、类型、起始、结束地址等),并保存在该设备的resource指针中即可。然后在设备probe时,设备需求会调用资源管理接口,分配、使用这些资源。而内核的资源管理逻辑,可以判断这些资源是否已被使用、是否可被使用等等。
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- struct resource {
- resource_size_t start;
- resource_size_t end;
- const char *name;
- unsigned long flags;
- struct resource *parent, *sibling, *child;
- };
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- 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),
- },
- };
从 device_driver 封装而来的platform_device_dirver
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- 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;
- };
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- 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
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- 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);
- }
Platform Device提供的API
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- /* 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。
arch_setup_pdev_archdata,设置platform_device变量中的archdata指针。
platform_get_resource、platform_get_irq、platform_get_resource_byname、platform_get_irq_byname,通过这些接口,可以获取platform_device变量中的resource信息,以及直接获取IRQ的number等等。
platform_device_register_full、platform_device_register_resndata、platform_device_register_simple、platform_device_register_data,其它形式的设备注册。调用者只需要提供一些必要的信息,如name、ID、resource等,Platform模块就会自动分配一个struct
platform_device变量,填充内容后,注册到内核中。
platform_device_alloc,以name和id为参数,动态分配一个struct platform_device变量。
platform_device_add_resources,向platform device中增加资源描述。
platform_device_add_data,向platform device中添加自定义的数据(保存在pdev->dev.platform_data指针中)。
platform_device_add、platform_device_del、platform_device_put,其它操作接口。
Platform Driver提供的API
platform_driver_registe、platform_driver_unregister,platform driver的注册、注销接口。
platform_driver_probe,主动执行probe动作。
platform_set_drvdata、platform_get_drvdata,设置或者获取driver保存在device变量中的私有数据。
懒人API
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- 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
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- #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");
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- #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");
转自:http://blog.csdn.net/lizuobin2/article/details/51607813