PHY设备驱动

1. 概述

        MAC控制器的驱动使用的是platform总线的连接方式，PHY设备驱动是基于device、driver、bus的连接方式。

        其驱动涉及如下几个重要部分：

总线 - sturct mii_bus (mii stand for media independent interface)

设备 - struct phy_device

驱动 - struct phy_driver

        phy设备不像i2c/spi有一个board_info函数进行设备的添加，而是直接读取phy中的寄存器<根据IEEE的规定，PHY芯片的前16个寄存器的内容必须是固定的>。

2. mdio_bus总线

2.1 总线注册的入口函数

# linux-4.9.225\drivers\net\phy\phy_device.c
static int __init phy_init(void)
{
	int rc;

	rc = mdio_bus_init(); //mdio_bus总线的注册
	if (rc)
		return rc;

	rc = phy_drivers_register(genphy_driver,ARRAY_SIZE(genphy_driver), THIS_MODULE); //通用PHY驱动
	if (rc)
		mdio_bus_exit();

	return rc;
}

subsys_initcall(phy_init); 

        subsys_initcall(phy_init) 这行的作用非常重要，这一行就决定了内核在启动的时候会调用该函数，注册完了之后紧接着又注册一个通用的PHY驱动。

2.2 总线注册函数— mdio_bus_init解析

# linux-4.9.225\drivers\net\phy\mdio_bus.c
static struct class mdio_bus_class = {
	.name		= "mdio_bus",
	.dev_release	= mdiobus_release,
};

static int mdio_bus_match(struct device *dev, struct device_driver *drv)
{
	struct mdio_device *mdio = to_mdio_device(dev);

	if (of_driver_match_device(dev, drv))
		return 1;

	if (mdio->bus_match)
		return mdio->bus_match(dev, drv);

	return 0;
}

struct bus_type mdio_bus_type = {
	.name		= "mdio_bus",     //总线名称
	.match		= mdio_bus_match, //用来匹配总线上设备和驱动的函数
	.pm		= MDIO_BUS_PM_OPS,
};
EXPORT_SYMBOL(mdio_bus_type);

int __init mdio_bus_init(void)
{
	int ret;

	ret = class_register(&mdio_bus_class); //注册设备类 (在linux设备模型中，我再仔细讲这个类的概念)
	if (!ret) {
		ret = bus_register(&mdio_bus_type);//总线注册
		if (ret)
			class_unregister(&mdio_bus_class);
	}

	return ret;
}

        其中

        (1) class_register(&mdio_bus_class)执行后会有以下设备类：

/sys/class/mdio_bus

        (2)bus_register(&mdio_bus_type)执行后会有以下总线类型：

/sys/bus/mdio_bus

2.3 总线中的match函数解析

/**
 * mdio_bus_match - determine if given MDIO driver supports the given
 *		    MDIO device
 * @dev: target MDIO device
 * @drv: given MDIO driver
 *
 * Description: Given a MDIO device, and a MDIO driver, return 1 if
 *   the driver supports the device.  Otherwise, return 0. This may
 *   require calling the devices own match function, since different classes
 *   of MDIO devices have different match criteria.
 */
static int mdio_bus_match(struct device *dev, struct device_driver *drv)
{
	struct mdio_device *mdio = to_mdio_device(dev);

	if (of_driver_match_device(dev, drv))
		return 1;

	if (mdio->bus_match)               //实现匹配的函数
		return mdio->bus_match(dev, drv);

	return 0;
}

3. 设备驱动的注册

        在phy_init函数中不仅注册了mdio_bus总线，还注册了一个通用的PHY驱动作为缺省的内核PHY驱动，但是如果PHY芯片的内部寄存器和802.3定义的并不一样或者需要特殊的功能配置以实现更强的功能，这就需要专有的驱动。

        对于市场上存在的主流PHY品牌，一般在内核源码 drivers\net\phy目录下都有对应的驱动。本节主要以realtek RTL8211F为例，讲述PHY的驱动，代码如下：

# linux-4.9.225\drivers\net\phy\realtek.c
static struct phy_driver realtek_drvs[] = {
	......
	, {
		.phy_id		= 0x001cc916,
		.name		= "RTL8211F Gigabit Ethernet",
		.phy_id_mask	= 0x001fffff,
		.features	= PHY_GBIT_FEATURES,
		.flags		= PHY_HAS_INTERRUPT,
		.config_aneg	= &genphy_config_aneg,
		.config_init	= &rtl8211f_config_init,
		.read_status	= &genphy_read_status,
		.ack_interrupt	= &rtl8211f_ack_interrupt,
		.config_intr	= &rtl8211f_config_intr,
		.suspend	= genphy_suspend,
		.resume		= genphy_resume,
	},
};

module_phy_driver(realtek_drvs);                           //注册PHY驱动

static struct mdio_device_id __maybe_unused realtek_tbl[] = {
	{ 0x001cc912, 0x001fffff },
	{ 0x001cc914, 0x001fffff },
	{ 0x001cc915, 0x001fffff },
	{ 0x001cc916, 0x001fffff },
	{ }
};

MODULE_DEVICE_TABLE(mdio, realtek_tbl);

3.1 phy驱动的注册

        同一品牌的PHY设备有多种不同的型号，内核为了支持一次可以注册多个型号的PHY的驱动，在include\linux\phy.h中提供了用于注册PHY驱动的宏module_phy_driver。该宏的定义如下：

# linux-4.9.225\include\linux\phy.h

#define phy_module_driver(__phy_drivers, __count)			\
static int __init phy_module_init(void)					\
{									\
	return phy_drivers_register(__phy_drivers, __count, THIS_MODULE); \
}	

#define module_phy_driver(__phy_drivers)				\
	phy_module_driver(__phy_drivers, ARRAY_SIZE(__phy_drivers))

       phy_driver_register定义如下(注意这里与老版本内核有一定的改动)

/**
 * phy_driver_register - register a phy_driver with the PHY layer
 * @new_driver: new phy_driver to register
 * @owner: module owning this PHY
 */
int phy_driver_register(struct phy_driver *new_driver, struct module *owner)
{
	int retval;

	new_driver->mdiodrv.flags |= MDIO_DEVICE_IS_PHY;
	new_driver->mdiodrv.driver.name = new_driver->name;//驱动名称
	new_driver->mdiodrv.driver.bus = &mdio_bus_type;   //驱动挂载的总线
	new_driver->mdiodrv.driver.probe = phy_probe;      //PHY设备和驱动匹配后调用的probe函数 
	new_driver->mdiodrv.driver.remove = phy_remove;
	new_driver->mdiodrv.driver.owner = owner;

	retval = driver_register(&new_driver->mdiodrv.driver); //向linux设备模型框架中注册device_driver驱动
	if (retval) {
		pr_err("%s: Error %d in registering driver\n",
		       new_driver->name, retval);

		return retval;
	}

	pr_debug("%s: Registered new driver\n", new_driver->name);

	return 0;
}

int phy_drivers_register(struct phy_driver *new_driver, int n,
			 struct module *owner)
{
	int i, ret = 0;

	for (i = 0; i < n; i++) {
		ret = phy_driver_register(new_driver + i, owner);//注册数组中所有的phy驱动
		if (ret) {
			while (i-- > 0)
				phy_driver_unregister(new_driver + i);
			break;
		}
	}
	return ret;
}

3.2 MODULE_DEVICE_TABLE(mdio, realtek_tbl)解析

宏定义展开后如下：

#define MODULE_DEVICE_TABLE(mdio, realtek_tbl)					\
extern const struct mdio_device_id __mod_mdio__realtek_tbl_device_table		\
  __attribute__ ((unused, "realtek_tbl")))

4. 设备驱动与控制器驱动之间的关系图