一：加载wifi驱动模块

    在hardware/libhardware_legacy/wifi/wifi.c调用函数

    insmod(DRIVER_MODULE_PATH, DRIVER_MODULE_ARG)

    其中

     DRIVER_MODULE_PATH = /system/lib/dhd.ko

      DRIVER_MODULE_ARG  = "firmware_path=/etc/wifi/40181/fw_bcm40181a2.bin nvram_path=/etc/wifi/40181/nvram.txt"

二：wifi驱动模块运行

     wifi驱动入口dhd_module_init(void) dhd_linux.c

dhd_module_init(void)
{
	int error = 0;

	DHD_TRACE(("%s: Enter\n", __FUNCTION__));

	wl_android_init(); //初始化dhd_msg_level |= DHD_ERROR_VAL,给iface_name赋值为wlan

	do {
		sema_init(&dhd_chipup_sem, 0);
		dhd_bus_reg_sdio_notify(&dhd_chipup_sem); //注册sdio driver,支持如下图wifi列表，sdio驱动获取wifi列表的设备后调用                                                                    //dummy_probe() --> up(dhd_chipup_sem);		dhd_customer_gpio_wlan_ctrl(WLAN_POWER_ON);
                
		if (down_timeout(&dhd_chipup_sem,        //2000ms超时等待dhd_chipup_sem			msecs_to_jiffies(POWERUP_WAIT_MS)) == 0) {
			dhd_bus_unreg_sdio_notify();
			chip_up = 1;
			break;
		}
		DHD_ERROR(("\nfailed to power up wifi chip, retry again (%d left) **\n\n",
			retry+1));
		dhd_bus_unreg_sdio_notify();
		dhd_customer_gpio_wlan_ctrl(WLAN_POWER_OFF);
	} while (retry-- > 0);

	if (!chip_up) {
		DHD_ERROR(("\nfailed to power up wifi chip, max retry reached, exits **\n\n"));
		return -ENODEV;
	}

	sema_init(&dhd_registration_sem, 0);

	error = dhd_bus_register();     //注册dhd_sdio驱动，最终会调用到dhd_net_attach();

	if (!error)
		printf("\n%s\n", dhd_version);
	else {
		DHD_ERROR(("%s: sdio_register_driver failed\n", __FUNCTION__));
		goto fail_1;
	}

	/*
	 * Wait till MMC sdio_register_driver callback called and made driver attach.
	 * It‘s needed to make sync up exit from dhd insmod  and
	 * Kernel MMC sdio device callback registration
	 */
	if ((down_timeout(&dhd_registration_sem,  //函数dhd_net_attach() --> up(&dhd_registration_sem);		msecs_to_jiffies(DHD_REGISTRATION_TIMEOUT)) != 0) ||
		(dhd_registration_check != TRUE)) {
		error = -ENODEV;
		DHD_ERROR(("%s: sdio_register_driver timeout or error \n", __FUNCTION__));
		goto fail_2;
	}

	wl_android_post_init();


	return error;

fail_2:
	dhd_bus_unregister();

fail_1:

	/* Call customer gpio to turn off power with WL_REG_ON signal */
	dhd_customer_gpio_wlan_ctrl(WLAN_POWER_OFF);

	return error;
}