WiFi驱动(1)框架解析

Linux：3.10
WiFi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.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_chip
static CLASS_ATTR(chip, 0664, wifi_chip_read, NULL);
// 生成class_attr_power
static 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。