linux：3.10WiFi芯片：RTL8723接口：SDIO
本文從硬件結構到軟件實現探究Linux中WiFi驅動的框架。如下圖：
硬件角度：CPUWiFi芯片，以rtl8723為例接口SDIO
軟件角度：1、電源、GPIO：負責WiFi模組的電源管理、IO管理2、SDIO：數據通道3、WiFi驅動：負責WiFi規范實現4、Sysfs：/sys/文件系統中提供訪問接口
Linux有非常好的模塊化機制，所以這幾部分作為各自獨立的模塊進行注冊，下面從代碼示例的方式看下。
一、電源、GPIO管理模塊
該模塊完成CPU對WiFi模組電源、引腳的初始化、控制等功能。由于Linux采用設備樹(Device Tree)方式管理硬件設置，所以第一步就是解析dts文件中的設置項并進行賦值、初始化操作，如：
static struct of_device_id wlan_platdata_of_match[] = {    { .compatible = "wlan-platdata" },    { }};MODULE_DEVICE_TABLE(of, wlan_platdata_of_match);static int wlan_platdata_parse_dt(struct device *dev, struct wifi_moudle *data){	struct device_node *node = dev->of_node;    ret = of_PRoperty_read_string(node, "wifi_chip_type", &strings);	ret = of_property_read_u32(node, "sdio_vref", &value);    of_find_property(node, "keep_wifi_power_on", NULL)    of_find_property(node, "vref_ctrl_enable", NULL)	of_find_property(node, "power_ctrl_by_pmu", NULL);	of_get_named_gpio_flags(node, "WIFI,poweren_gpio", 0, &flags);    of_get_named_gpio_flags(node, "WIFI,reset_gpio", 0, &flags);    of_get_named_gpio_flags(node, "WIFI,host_wake_irq", 0, &flags);    return 0;}除此以外，還需要導出設置方式，以供其他模塊進行需要的設置，如：
EXPORT_SYMBOL(get_wifi_chip_type);驅動以平臺驅動的方式進行注冊：
static struct platform_driver wlan_driver = {	.probe = wlan_probe,	.remove = wlan_remove,    .suspend = wlan_suspend,    .resume = wlan_resume,	.driver = {		.name = "wlan-platdata",		.owner = THIS_MODULE,        .of_match_table = of_match_ptr(wlan_platdata_of_match),	},};static int wlan_probe(struct platform_device *pdev){	......	wlan_platdata_parse_dt(&pdev->dev, pdata);	......}static int __init wlan_init(void){    LOG("Enter %s/n", __func__);	return platform_driver_register(&wlan_driver);}module_init(wlan_init);module_exit(wlan_exit);
二、SDIO Host端
CPU集成由SDIO控制器，所以Host端就是對CPU上SDIO控制器的編程、使用，然后把函數指針賦予Core層(分層思想)。這部分代碼一般存在于drivers/mmc/host/目錄。操作接口比如：
static const struct mmc_host_ops dw_mci_ops = {	.request		= dw_mci_request,	.pre_req		= dw_mci_pre_req,	.post_req		= dw_mci_post_req,	.set_ios		= dw_mci_set_ios,	.get_ro			= dw_mci_get_ro,	.get_cd			= dw_mci_get_cd,	.set_sdio_status	= dw_mci_set_sdio_status,	.hw_reset		= dw_mci_hw_reset,	.enable_sdio_irq	= dw_mci_enable_sdio_irq,	.execute_tuning		= dw_mci_execute_tuning,        .post_tmo		= dw_mci_post_tmo,	#ifdef CONFIG_MMC_DW_ROCKCHIP_SWITCH_VOLTAGE        .start_signal_voltage_switch				= dw_mci_start_signal_voltage_switch,        .card_busy		= dw_mci_card_busy,        #endif};
三、SDIO Client端
WiFi模組自身集成有SDIO控制器，所以這部分完成對WiFi模組上SDIO控制器的編程、使用。針對RTL8723，SDIO Client的代碼實現在其驅動源碼里。如下：
rtl8723：static struct sdio_drv_priv sdio_drvpriv = {	.r871xs_drv.probe = rtw_drv_init,	.r871xs_drv.remove = rtw_dev_remove,	.r871xs_drv.name = (char*)DRV_NAME,	.r871xs_drv.id_table = sdio_ids,	#if (LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,29)) 	.r871xs_drv.drv = {		.pm = &rtw_sdio_pm_ops,	}	#endif};static int rtw_drv_entry(void){	sdio_drvpriv.drv_registered = _TRUE;	// sdio_register_driver: kernel/drivers/mmc/core/sdio_bus.c	ret = sdio_register_driver(&sdio_drvpriv.r871xs_drv);	return ret;}	int rtl8723_wifi_init_module(void){	return rtw_drv_entry();}late_initcall(rtl8723_wifi_init_module);
四、Sysfs
通過sys文件系統，用戶可以讀寫驅動信息。
static ssize_t wifi_chip_read(struct class *cls, struct class_attribute *attr, char *_buf){	ssize_t count = sprintf(_buf, "%s", "RTL8723BS");	printk("Current WiFi chip is RTL8723BS./n");	return count;}static ssize_t wifi_power_write(struct class *cls, struct class_attribute *attr, const char *_buf, size_t _count){	int poweren = 0;    poweren = simple_strtol(_buf, NULL, 10);    if(poweren > 0) {        wifi_power(1);    } else {        wifi_power(0);    }	return _count;}static struct class *wifi_class = NULL;// 生成class_attr_chipstatic CLASS_ATTR(chip, 0664, wifi_chip_read, NULL);// 生成class_attr_powerstatic CLASS_ATTR(power, 0660, NULL, wifi_power_write);int wifi_sysif_init(void){    int ret;    wifi_class = class_create(THIS_MODULE, "rtlwifi");        ret = class_create_file(wifi_class, &class_attr_chip);    ret = class_create_file(wifi_class, &class_attr_power);    return 0;}void wifi_sysif_exit(void){    // need to remove the sys files and class    class_remove_file(wifi_class, &class_attr_chip);    class_remove_file(wifi_class, &class_attr_power);            wifi_class = NULL;}module_init(wifi_sysif_init);module_exit(wifi_sysif_exit);該模塊注冊后，將出現/sys/class/rtlwifi目錄，且目錄下含有/sys/class/rtlwifi/chip、/sys/class/rtlwifi/power兩個文件，cat chip文件將會得到RTL8723BS，而讀寫power文件能夠獲取、設置WiFi模組供電狀態。