Linux 驱动设备匹配过程

一、Linux 驱动-总线-设备模型

1、驱动分层

Linux内核需要兼容多个平台，不同平台的寄存器设计不同导致操作方法不同，故内核提出分层思想，抽象出与硬件无关的软件层作为核心层来管理下层驱动，各厂商根据自己的硬件编写驱动代码作为硬件驱动层

2、设备&总线&驱动

Linux内核建立的设备-总线-驱动模型，定义如下：

1、device
include\linux\device.h
struct device {...struct bus_type	*bus;		  /* type of bus device is on */struct device_driver *driver; /* which driver has allocated this device */struct device_node	*of_node; /* associated device tree node */...
}2、driver
include\linux\device\driver.h
struct device_driver {...struct bus_type		*bus;...
}3、bus
include\linux\bus\bus.h
struct bus_type {...int (*match)(struct device *dev, struct device_driver *drv);int (*probe)(struct device *dev);...
}

这里提到的是虚拟总线，总线能将对应的设备和驱动进行匹配，可以用下面的命令查看不同总线类型

/sys/bus # ls -l 
......
drwxr-xr-x 4 root root 0 2023-02-21 13:35 i2c
drwxr-xr-x 4 root root 0 2023-02-21 13:35 mmc
drwxr-xr-x 5 root root 0 2023-02-21 13:35 pci
drwxr-xr-x 4 root root 0 2023-02-20 07:09 platform
drwxr-xr-x 4 root root 0 2023-02-21 13:35 scsi
drwxr-xr-x 4 root root 0 2023-02-21 13:35 usb
......

总线类型	描述
I2C总线	挂在i2c总线(硬件)下的从设备，比如加密芯片、rtc芯片、触摸屏芯片等等都需要驱动，自然也要按照分离思想来设计。内核中的i2c 总线就是用来帮助i2c从设备的设备信息和驱动互相匹配的
Platform总线	像i2c、spi这样硬件有实体总线的，从设备驱动可以用总线来管理。那么没有总线的硬件外设怎么办？比如gpio、uart、i2c控制器、spi 控制器…等等，这些通通用 platform 总线来管理

二、驱动匹配设备过程简述

在写驱动时会用到一些注册函数比如：platform_driver_register，spi_register_driver、i2c_add_driver，接下来分析内核驱动和设备匹配的流程，原理就是在注册到总线的时候，去获取对方的链表并根据规则检测，匹配后调用probe()，也就是驱动的入口函数

以Platform Driver举例，整个匹配过程如下

2.1 整体调用逻辑

module_platform_driver|-- module_driver|-- __platform_driver_register|-- driver_register|-- bus_add_driver|-- driver_attach|-- bus_for_each_dev|-- __driver_attach|-- driver_match_device|-- platform_match|-- of_driver_match_device|-- of_match_device|-- __of_match_node|-- driver_probe_device|-- really_probe|-- call_driver_probe|-- platform_probe|-- drv->probe()

2.2 module_platform_driver

封装了一层，展开后实际上就是module_init和module_exit

/* module_platform_driver() - Helper macro for drivers that don't do* anything special in module init/exit.  This eliminates a lot of* boilerplate.  Each module may only use this macro once, and* calling it replaces module_init() and module_exit()*/
#define module_platform_driver(__platform_driver) \module_driver(__platform_driver, platform_driver_register, \platform_driver_unregister)

例如对于MTK某平台UFS驱动，传入__platform_driver 参数为

static struct platform_driver ufs_mtk_pltform = {.probe      = ufs_mtk_probe,.remove     = ufs_mtk_remove,.shutdown   = ufshcd_pltfrm_shutdown,.driver = {.name   = "ufshcd-mtk",.pm     = &ufs_mtk_pm_ops,.of_match_table = ufs_mtk_of_match,},
};

2.3 module_driver

/*** module_driver() - Helper macro for drivers that don't do anything* special in module init/exit. This eliminates a lot of boilerplate.* Each module may only use this macro once, and calling it replaces* module_init() and module_exit().** @__driver: driver name* @__register: register function for this driver type* @__unregister: unregister function for this driver type* @...: Additional arguments to be passed to __register and __unregister.** Use this macro to construct bus specific macros for registering* drivers, and do not use it on its own.*/
#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);

2.4 __platform_driver_register

注意此处的__register是传进来的__platform_driver_register

/*** __platform_driver_register - register a driver for platform-level devices* @drv: platform driver structure* @owner: owning module/driver*/
int __platform_driver_register(struct platform_driver *drv,struct module *owner)
{drv->driver.owner = owner;drv->driver.bus = &platform_bus_type;return driver_register(&drv->driver);
}
EXPORT_SYMBOL_GPL(__platform_driver_register);

对bus参数进行赋值

struct bus_type platform_bus_type = {.name		= "platform",.dev_groups	= platform_dev_groups,.match	= platform_match,.uevent	= platform_uevent,.probe	= platform_probe,.remove	= platform_remove,.shutdown	= platform_shutdown,.dma_configure= platform_dma_configure,.dma_cleanup= platform_dma_cleanup,.pm	= &platform_dev_pm_ops,
};
EXPORT_SYMBOL_GPL(platform_bus_type);

2.5 driver_register

/*** driver_register - register driver with bus* @drv: driver to register** We pass off most of the work to the bus_add_driver() call,* since most of the things we have to do deal with the bus* structures.*/
int driver_register(struct device_driver *drv)
{......other = driver_find(drv->name, drv->bus);if (other) {pr_err("Error: Driver '%s' is already registered, ""aborting...\n", drv->name);return -EBUSY;}ret = bus_add_driver(drv);......
}
EXPORT_SYMBOL_GPL(driver_register);

2.6 bus_add_driver

drv->bus->p->drivers_autoprobe默认是1，结构体定义时就赋值了

struct subsys_private {...unsigned int drivers_autoprobe:1;    
}

/*** bus_add_driver - Add a driver to the bus.* @drv: driver.*/
int bus_add_driver(struct device_driver *drv)
{......if (drv->bus->p->drivers_autoprobe) {error = driver_attach(drv);if (error)goto out_del_list;}......
}

2.7 driver_attach

/*** driver_attach - try to bind driver to devices.* @drv: driver.** Walk the list of devices that the bus has on it and try to* match the driver with each one.  If driver_probe_device()* returns 0 and the @dev->driver is set, we've found a* compatible pair.*/
int driver_attach(struct device_driver *drv)
{return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}
EXPORT_SYMBOL_GPL(driver_attach);

2.8 bus_for_each_dev

此函数 fn 即为 __driver_attach 函数指针，data参数是 drv

int bus_for_each_dev(struct bus_type *bus, struct device *start,void *data, int (*fn)(struct device *, void *))
{struct klist_iter i;struct device *dev;int error = 0;if (!bus || !bus->p)return -EINVAL;klist_iter_init_node(&bus->p->klist_devices, &i,(start ? &start->p->knode_bus : NULL));while (!error && (dev = next_device(&i)))error = fn(dev, data);klist_iter_exit(&i);return error;
}
EXPORT_SYMBOL_GPL(bus_for_each_dev);

2.9 __driver_attach

static int __driver_attach(struct device *dev, void *data){......ret = driver_match_device(drv, dev);......ret = driver_probe_device(drv, dev);......
}

2.9.1.1 driver_match_device

static inline int driver_match_device(struct device_driver *drv,struct device *dev)
{return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}/* 返回 1 是可以继续往下走的 ret <= 0 不行*/

可以看到在Register时有match回调

struct bus_type platform_bus_type = {.......match	= platform_match,.probe	= platform_probe,......
};

2.9.1.2 platform_match

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);
}

2.9.1.3 of_driver_match_device

/*** 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;
}

of_match_table定义如下

static struct platform_driver ufs_mtk_pltform = {.probe      = ufs_mtk_probe,.remove     = ufs_mtk_remove,.shutdown   = ufshcd_pltfrm_shutdown,.driver = {.name   = "ufshcd-mtk",.pm     = &ufs_mtk_pm_ops,.of_match_table = ufs_mtk_of_match,},
};
static const struct of_device_id ufs_mtk_of_match[] = {{ .compatible = "mediatek,mtxxxx-ufshci" },
};

2.9.1.4 of_match_device

const struct of_device_id *of_match_device(const struct of_device_id *matches,const struct device *dev)
{if (!matches || !dev->of_node || dev->of_node_reused)return NULL;return of_match_node(matches, dev->of_node);
}
EXPORT_SYMBOL(of_match_device);

2.9.1.5 of_match_node

const struct of_device_id *of_match_node(const struct of_device_id *matches,const struct device_node *node)
{match = __of_match_node(matches, node);
}
EXPORT_SYMBOL(of_match_node);

2.9.1.6 __of_match_node

static
const struct of_device_id *__of_match_node(const struct of_device_id *matches,const struct device_node *node)
{for (; matches->name[0] ||matches->type[0] || matches->compatible[0]; matches++) { /* 每次循环，选择Vendor驱动中的match table结构体数组的下一个比较 */score = __of_device_is_compatible(node, matches->compatible,matches->type, matches->name);if (score > best_score) {best_match = matches;best_score = score;}}return best_match;
}

2.9.1.7 __of_device_is_compatible

static int __of_device_is_compatible(const struct device_node *device,const char *compat, const char *type, const char *name)
{......if (of_compat_cmp(cp, compat, strlen(compat)) == 0) {score = INT_MAX/2 - (index << 2);break;}......
}

cp即为从设备树节点中获取的compatible信息，示例如下

ufshci: ufshci@112b0000 {compatible = "mediatek,mtxxxx-ufshci";reg = <0 0x112b0000 0 0x2a00>;
}

2.9.2.1 driver_probe_device

static int driver_probe_device(struct device_driver *drv, struct device *dev)
{......ret = __driver_probe_device(drv, dev);......
}

2.9.2.2 __driver_probe_device

initcall_debug是一个内核参数，可以跟踪initcall，用来定位内核初始化的问题。在cmdline中增加initcall_debug后，内核启动过程中会在调用每一个init函数前有一句打印，结束后再有一句打印并且输出了该Init函数运行的时间，通过这个信息可以用来定位启动过程中哪个init函数运行失败以及哪些init函数运行时间较长

really_probe_debug()内部还是调用了really _probe()

static int __driver_probe_device(struct device_driver *drv, struct device *dev)
{......if (initcall_debug)ret = really_probe_debug(dev, drv);elseret = really_probe(dev, drv);......
}

2.9.2.3 really_probe

static int really_probe(struct device *dev, struct device_driver *drv)
{......ret = call_driver_probe(dev, drv);......
}

2.9.2.4 call_driver_probe

static int call_driver_probe(struct device *dev,struct device_driver *drv)
{......if (dev->bus->probe)ret = dev->bus->probe(dev);else if (drv->probe)ret = drv->probe(dev);......
}

2.9.2.5 platform_probe

不管走没有dev->bus->probe，最终都会走到drv->probe

static int platform_probe(struct device *_dev)
{struct platform_driver *drv = to_platform_driver(_dev->driver);struct platform_device *dev = to_platform_device(_dev);......if (drv->probe) {ret = drv->probe(dev);if (ret)dev_pm_domain_detach(_dev, true);}......
}

此时驱动匹配设备成功，会走到之前Register的probe

static struct platform_driver ufs_mtk_pltform = {.probe      = ufs_mtk_probe,......
};

【参考博客】

[1] Linux设备驱动和设备匹配过程_linux驱动和设备匹配过程-CSDN博客

[2] platform 总线_怎么查询platform 总线-CSDN博客

[3] Linux Driver 和Device匹配过程分析（1）_linux设备驱动和设备树的match过程-CSDN博客