4.1.2. platform驱动
4.1.2.1. 数据结构
linux内核使用bus_type结构体表示总线
[include/linux/device.h]
struct bus_type {
const char *name; //总线名字
const char *dev_name;
struct device *dev_root;
const struct attribute_group **bus_groups; //总线属性
const struct attribute_group **dev_groups; //设备属性
const struct attribute_group **drv_groups; //驱动属性
int (*match)(struct device *dev, struct device_driver *drv);
int (*uevent)(struct device *dev, struct kobj_uevent_env *env);
int (*probe)(struct device *dev);
int (*remove)(struct device *dev);
void (*shutdown)(struct device *dev);
int (*online)(struct device *dev);
int (*offline)(struct device *dev);
int (*suspend)(struct device *dev, pm_message_t state);
int (*resume)(struct device *dev);
int (*num_vf)(struct device *dev);
int (*dma_configure)(struct device *dev);
const struct dev_pm_ops *pm;
const struct iommu_ops *iommu_ops;
struct subsys_private *p;
struct lock_class_key lock_key;
bool need_parent_lock;
};
platform总线是bus_type的一个具体实例
[drivers/base/platform.c]
struct bus_type platform_bus_type = {
.name = "platform",
.dev_groups = platform_dev_groups,
.match = platform_match,
.uevent = platform_uevent,
.dma_configure = platform_dma_configure,
.pm = &platform_dev_pm_ops,
};
EXPORT_SYMBOL_GPL(platform_bus_type);
linux设备驱动模型下的总线都有两个重要的结构体:描述设备和驱动的结构体
[include/linux/platform_device.h]
struct platform_device {
const char *name;
int id;
bool id_auto;
struct device dev; //嵌入device结构体
u64 platform_dma_mask;
u32 num_resources;
struct resource *resource;
const struct platform_device_id *id_entry;
char *driver_override; /* Driver name to force a match */
/* MFD cell pointer */
struct mfd_cell *mfd_cell;
/* arch specific additions */
struct pdev_archdata archdata;
};
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; //嵌入device_driver结构体
const struct platform_device_id *id_table;
bool prevent_deferred_probe;
};
4.1.2.2. platform驱动和设备的匹配
platform_bus_type是platform平台总线，其中platfrom_match就是匹配函数
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);
/* When driver_override is set, only bind to the matching driver */
if (pdev->driver_override)
return !strcmp(pdev->driver_override, drv->name);
/* Attempt an OF style match first */
if (of_driver_match_device(dev, drv))
return 1;
/* Then try ACPI style match */
if (acpi_driver_match_device(dev, drv))
return 1;
/* Then try to match against the id table */
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);
}
4.1.2.2.1. of设备树匹配
OF类型的匹配，也就是设备树采用的匹配方式，Of_driver_match_device函数在文件include/linux/of_device.h中，device_driver结构体(表示设备驱动)中有个名为 of_match_table的成员变量，此成员变量保存着驱动的compatible匹配表，设备树中每个设备节点的compatible属性会和of_match_table表中的所有成员进行比较，查看 是否有相同的条目,如果有则表示设备和驱动匹配，匹配成功后probe函数就会执行
函数原型如下
/**
* of_driver_match_device - Tell if a driver's of_match_table matches a device.
* @drv: the device_driver structure to test
* @dev: the device structure to match against
*/
static inline int of_driver_match_device(struct device *dev,
const struct device_driver *drv)
{
return of_match_device(drv->of_match_table, dev) != NULL;
}
device_driver结构体如下
struct device_driver {
const char *name;
struct bus_type *bus;
struct module *owner;
const char *mod_name; /* used for built-in modules */
bool suppress_bind_attrs; /* disables bind/unbind via sysfs */
const struct of_device_id *of_match_table;
const struct acpi_device_id *acpi_match_table;
int (*probe) (struct device *dev);
int (*remove) (struct device *dev);
void (*shutdown) (struct device *dev);
int (*suspend) (struct device *dev, pm_message_t state);
int (*resume) (struct device *dev);
const struct attribute_group **groups;
const struct dev_pm_ops *pm;
struct driver_private *p;
};
of_match_table就是采用设备树的时候驱动使用的匹配表,类型为of_device_id
struct of_device_id {
char name[32];
char type[32];
char compatible[128];
const void *data;
};
示例如下
static const struct of_device_id omap_rtc_of_match[] = {
{
.compatible = "ti,am3352-rtc",
.data = &omap_rtc_am3352_type,
}, {
.compatible = "ti,da830-rtc",
.data = &omap_rtc_da830_type,
}, {
/* sentinel */
}
};
MODULE_DEVICE_TABLE(of, omap_rtc_of_match);
static struct platform_driver omap_rtc_driver = {
.probe = omap_rtc_probe,
.remove = omap_rtc_remove,
.shutdown = omap_rtc_shutdown,
.driver = {
.name = "omap_rtc",
.pm = &omap_rtc_pm_ops,
.of_match_table = omap_rtc_of_match,
},
.id_table = omap_rtc_id_table,
};
4.1.2.2.2. acpi匹配
如果of_driver_match_device没有匹配到则使用acpi进行匹配。首先从device中找到对应的acpi_device，找到acpi_device设备后就可以进行匹配了。acpi设备使用两种方式匹配
[drivers/acpi/bus.c]
bool acpi_driver_match_device(struct device *dev,
const struct device_driver *drv)
{
if (!drv->acpi_match_table)
return acpi_of_match_device(ACPI_COMPANION(dev),
drv->of_match_table,
NULL);
return __acpi_match_device(acpi_companion_match(dev),
drv->acpi_match_table, drv->of_match_table,
NULL, NULL);
}
EXPORT_SYMBOL_GPL(acpi_driver_match_device);
4.1.2.2.3. id_table匹配
id_table匹配，每个platform_driver结构体有一个id_table成员变量，顾名思义，保存了很多id信息。这些id信息存放着这个platform驱动所支持的驱动类型
示例如下
static const struct platform_device_id omap_rtc_id_table[] = {
{
.name = "omap_rtc",
.driver_data = (kernel_ulong_t)&omap_rtc_default_type,
}, {
.name = "am3352-rtc",
.driver_data = (kernel_ulong_t)&omap_rtc_am3352_type,
}, {
.name = "da830-rtc",
.driver_data = (kernel_ulong_t)&omap_rtc_da830_type,
}, {
/* sentinel */
}
};
4.1.2.2.4. name匹配
如果前三种方式都不存在的话，就直接比较驱动和设备的那么字段，看看是否相同
static struct platform_driver omap_rtc_driver = {
.probe = omap_rtc_probe,
.remove = omap_rtc_remove,
.shutdown = omap_rtc_shutdown,
.driver = {
.name = "omap_rtc", //此字段为device和driver匹配的最后一种方式
.pm = &omap_rtc_pm_ops,
.of_match_table = omap_rtc_of_match,
},
.id_table = omap_rtc_id_table,
};
4.1.2.3. platform总线下的驱动编写流程
首先定义一个platform_driver结构体变量
然后实现结构体中各个成员变量，重点是实现匹配方式以及probe函数
当我们定义并初始化好platform_driver结构体变量以后，需要在驱动入口函数里面调用platform_driver_register函数向内核注册一个platform驱动
驱动卸载函数中通过platform_driver_unregister函数卸载
框架流程如下
struct xxx_dev{
struct cdev cdev;
/* 设备结构体其他具体内容 */
};
struct xxx_dev xxxdev; /* 定义个设备结构体变量 */
static int xxx_open(struct inode *inode, struct file *filp)
{
/* 函数具体内容 */
return 0;
}
static ssize_t xxx_write(struct file *filp, const char __user *buf,
size_t cnt, loff_t *offt)
{
/* 函数具体内容 */
return 0;
}
/*
* 字符设备驱动操作集
*/
static struct file_operations xxx_fops = {
.owner = THIS_MODULE,
.open = xxx_open,
.write = xxx_write,
};
/*
* platform 驱动的 probe 函数
* 驱动与设备匹配成功以后此函数就会执行
*/
static int xxx_probe(struct platform_device *dev)
{
......
cdev_init(&xxxdev.cdev, &xxx_fops); /* 注册字符设备驱动 */
/* 函数具体内容 */
return 0;
}
static int xxx_remove(struct platform_device *dev)
{
......
cdev_del(&xxxdev.cdev);/* 删除 cdev */
/* 函数具体内容 */
return 0;
}
/* 匹配列表 */
static const struct of_device_id xxx_of_match[] = {
{
.compatible = "xxx-gpio" },
{
/* Sentinel */ }
};
/*
* platform 平台驱动结构体
*/
static struct platform_driver xxx_driver = {
.driver = {
.name = "xxx",
.of_match_table = xxx_of_match,
},
.probe = xxx_probe,
.remove = xxx_remove,
};
/* 驱动模块加载 */
static int __init xxxdriver_init(void)
{
return platform_driver_register(&xxx_driver);
}
/* 驱动模块卸载 */
static void __exit xxxdriver_exit(void)
{
platform_driver_unregister(&xxx_driver);
}
module_init(xxxdriver_init);
module_exit(xxxdriver_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("yinwg");