WiFi驱动(1)框架解析

Linux：3.10WiFi芯片：RTL8723接口：SDIO

本文从硬件结构到软件实现探究Linux中WiFi驱动的框架。如下图：

硬件角度：

• CPU

• WiFi芯片，以rtl8723为例

• 总线SDIO
  

软件角度：

• 电源、GPIO：负责WiFi模组的电源管理、IO管理

• SDIO：数据通道

• WiFi驱动：负责WiFi规范实现

• Sysfs：/sys/文件系统中提供访问驱动接口

Linux有非常好的模块化机制，所以这几部分作为各自独立的模块进行注册，下面从代码示例的方式看下。

一、电源、GPIO管理模块

该模块完成CPU对WiFi模组电源、引脚的初始化、控制等功能。由于Linux采用设备树(Device Tree)方式管理硬件设置，所以第一步就是解析dts文件中的设置项并进行赋值、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;}

驱动以平台驱动的方式进行注册：

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集成有SDIO控制器，所以Host端就是对CPU上SDIO控制器的驱动实现，然后把函数指针通过mmc_add_host()赋予Core层。这部分代码存在于drivers\mmc\host\目录。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_SWITCH_VOLTAGE        .start_signal_voltage_switch= dw_mci_start_signal_voltage_switch,        .card_busy= dw_mci_card_busy,        #endif};

添加Host：

struct mmc_host *mmc;mmc = mmc_alloc_host(sizeof(struct dw_mci_slot), host->dev);mmc->ops = &dw_mci_ops;mmc_add_host(mmc);

三、SDIO Client端

WiFi模组自身集成有SDIO控制器，所以这部分完成对WiFi模组上SDIO控制器的驱动实现。针对RTL8723，SDIO Client的代码实现在其驱动源码里。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.cret = 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

通过sys文件系统，用户可以读写驱动信息。

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);

该模块注册后，将出现/sys/class/rtlwifi目录，且目录下含有/sys/class/rtlwifi/chip、/sys/class/rtlwifi/power两个文件，cat chip文件将会得到RTL8723BS，而读写power文件能够获取、设置WiFi模组供电状态。