Linux USB-Wifi Driver
1. USB设备枚举过程
设备在插入USB 接口到设备成功找到它自己的驱动这一过程为：当把USB 设备插到USB 接口上后，USB 中央控制器会检测到有设备插入USB 接口了，Linux 内核会给设备分配一个数据结构来代表这个设备，Linux 会分配一个struct usb_device 数据结构来代表该设备，该数据结构记录设备的一些属性及数据。并把该数据结构挂载到一个全局的USB 设备链上。在这一期间主机通过0 号端点得知了设备的一些信息，并知道了设备的厂家号和产品号。然后到一个全局的USB 驱动链上查找(通过调用驱动的probe函数来询问)，看看哪个驱动程序支持的设备列表中有该设备的厂家号和产品号。当找到后设备就和驱动匹配上了。
2. 关键数据结构
1) struct cfg80211_ops ：backend description for wireless configuration
2) struct wiphy：wireless hardware description
3) struct ieee80211_ops：callbacks from mac80211 to the driver
4) struct ieee80211_hw：hardware information and state
5) struct ieee80211_channel：channel definition
6) struct usb_driver：identifies USB interface driver to usbcore
3. USB-Wifi驱动架构
USB-Wifi驱动架构如下图所示：
1) ieee802.11 协议层
Linux Kernel中有ieee802.11 协议子层，各个不同型号的硬件设备驱动程序都是实现ieee80211_ops 数据结构中的函数，例如打开是start()函数，发送是tx()函数，关闭是stop()函数，睡眠是suspend函数，唤醒是resume函数等。
其代码位于： kernel/net/mac80211
2) USB无线网卡驱动层
由上图可见，USB无线网卡驱动层位于USB与802.11协议层之间，为了使其可正常工作，它必须搞好上下级关系：
a) 向USB Core注册USB驱动，通过USB通道收发数据
b) 向ieee802.11注册ieee80211_ops，以供ieee80211随时召唤，然后通过USB通道进行数据传输
3.1 向USB Core注册USB驱动
向USB Core注册USB驱动，通过USB通道收发数据，如我的代码为：
kernel/drivers/net/wireless/ath/ath9k/hif_usb.c
static struct usb_driver ath9k_hif_usb_driver = { //USB 驱动
.name = KBUILD_MODNAME,
.probe = ath9k_hif_usb_probe,
.disconnect = ath9k_hif_usb_disconnect,
#ifdef CONFIG_PM
.suspend = ath9k_hif_usb_suspend,
.resume = ath9k_hif_usb_resume,
.reset_resume = ath9k_hif_usb_resume,
#endif
.id_table = ath9k_hif_usb_ids,
.soft_unbind = 1,
};
int ath9k_hif_usb_init(void)
{
return usb_register(&ath9k_hif_usb_driver); // 把driver注册到USB驱动链中
}
void ath9k_hif_usb_exit(void)
{
usb_deregister(&ath9k_hif_usb_driver); // 把driver从USB驱动链中删除
}
3.2 向ieee802.11注册ieee80211_ops
向ieee802.11注册ieee80211_ops，以供ieee80211随时召唤，然后通过USB通道进行数据传输，如我的代码为：
在kernel/drivers/net/wireless/ath/ath9k/htc_drv_main.c中定义了ath9k_htc_ops，其详细定义如下：
struct ieee80211_ops ath9k_htc_ops = {
.tx = ath9k_htc_tx,
.start = ath9k_htc_start,
.stop = ath9k_htc_stop,
.add_interface = ath9k_htc_add_interface,
.remove_interface = ath9k_htc_remove_interface,
.config = ath9k_htc_config,
.configure_filter = ath9k_htc_configure_filter,
.sta_add = ath9k_htc_sta_add,
.sta_remove = ath9k_htc_sta_remove,
.conf_tx = ath9k_htc_conf_tx,
.bss_info_changed = ath9k_htc_bss_info_changed,
.set_key = ath9k_htc_set_key,
.get_tsf = ath9k_htc_get_tsf,
.set_tsf = ath9k_htc_set_tsf,
.reset_tsf = ath9k_htc_reset_tsf,
.ampdu_action = ath9k_htc_ampdu_action,
.sw_scan_start = ath9k_htc_sw_scan_start,
.sw_scan_complete = ath9k_htc_sw_scan_complete,
.set_rts_threshold = ath9k_htc_set_rts_threshold,
.rfkill_poll = ath9k_htc_rfkill_poll_state,
.set_coverage_class = ath9k_htc_set_coverage_class,
.set_bitrate_mask = ath9k_htc_set_bitrate_mask,
};
ath9k_htc_ops注册流程如下图所示：
ieee80211_alloc_hw()函数是即分配了802.11 协议层需要的内存结构，又顺便分配了驱动的私有数据结构，该函数分配的内存结构如下图所示：
/* Ensure 32-byte alignment of our private data and hw private data. * We use the wiphy priv data for both our ieee80211_local and for * the driver's private data * * In memory it'll be like this: * * +-------------------------+ * | struct wiphy | * +-------------------------+ * | struct ieee80211_local | * +-------------------------+ * | driver's private data | * +-------------------------+ * */
4. Wifi工作流程
4.1 Wifi打开基本流程
Wifi打开基本流程如下图所示：
4.2 Wifi关闭基本流程
Wifi关闭基本流程如下图所示：
4.3 Wifi待机和唤醒流程
5. 注册ieee80211_class
其详细代码如下：
net/wireless/sysfs.c
struct class ieee80211_class = {
.name = "ieee80211",
.owner = THIS_MODULE,
.dev_release = wiphy_dev_release,
.dev_attrs = ieee80211_dev_attrs,
#ifdef CONFIG_HOTPLUG
.dev_uevent = wiphy_uevent,
#endif
.suspend = wiphy_suspend, // Suspend Wifi
.resume = wiphy_resume, // Resume Wifi
.ns_type = &net_ns_type_operations,
.namespace = wiphy_namespace,
};
int wiphy_sysfs_init(void)
{
return class_register(&ieee80211_class);
}
void wiphy_sysfs_exit(void)
{
class_unregister(&ieee80211_class);
}
它需要调用的struct cfg80211_ops定义如下：
net/mac80211/cfg.c
struct cfg80211_ops mac80211_config_ops = {
.add_virtual_intf = ieee80211_add_iface,
.del_virtual_intf = ieee80211_del_iface,
.change_virtual_intf = ieee80211_change_iface,
.add_key = ieee80211_add_key,
.del_key = ieee80211_del_key,
.get_key = ieee80211_get_key,
.set_default_key = ieee80211_config_default_key,
.set_default_mgmt_key = ieee80211_config_default_mgmt_key,
.add_beacon = ieee80211_add_beacon,
.set_beacon = ieee80211_set_beacon,
.del_beacon = ieee80211_del_beacon,
.add_station = ieee80211_add_station,
.del_station = ieee80211_del_station,
.change_station = ieee80211_change_station,
.get_station = ieee80211_get_station,
.dump_station = ieee80211_dump_station,
.dump_survey = ieee80211_dump_survey,
#ifdef CONFIG_MAC80211_MESH
.add_mpath = ieee80211_add_mpath,
.del_mpath = ieee80211_del_mpath,
.change_mpath = ieee80211_change_mpath,
.get_mpath = ieee80211_get_mpath,
.dump_mpath = ieee80211_dump_mpath,
.update_mesh_config = ieee80211_update_mesh_config,
.get_mesh_config = ieee80211_get_mesh_config,
.join_mesh = ieee80211_join_mesh,
.leave_mesh = ieee80211_leave_mesh,
#endif
.change_bss = ieee80211_change_bss,
.set_txq_params = ieee80211_set_txq_params,
.set_channel = ieee80211_set_channel,
.suspend = ieee80211_suspend,
.resume = ieee80211_resume,
.scan = ieee80211_scan,
.sched_scan_start = ieee80211_sched_scan_start,
.sched_scan_stop = ieee80211_sched_scan_stop,
.auth = ieee80211_auth,
.assoc = ieee80211_assoc,
.deauth = ieee80211_deauth,
.disassoc = ieee80211_disassoc,
.join_ibss = ieee80211_join_ibss,
.leave_ibss = ieee80211_leave_ibss,
.set_wiphy_params = ieee80211_set_wiphy_params,
.set_tx_power = ieee80211_set_tx_power,
.get_tx_power = ieee80211_get_tx_power,
.set_wds_peer = ieee80211_set_wds_peer,
.rfkill_poll = ieee80211_rfkill_poll,
CFG80211_TESTMODE_CMD(ieee80211_testmode_cmd)
.set_power_mgmt = ieee80211_set_power_mgmt,
.set_bitrate_mask = ieee80211_set_bitrate_mask,
.remain_on_channel = ieee80211_remain_on_channel,
.cancel_remain_on_channel = ieee80211_cancel_remain_on_channel,
.mgmt_tx = ieee80211_mgmt_tx,
.mgmt_tx_cancel_wait = ieee80211_mgmt_tx_cancel_wait,
.set_cqm_rssi_config = ieee80211_set_cqm_rssi_config,
.mgmt_frame_register = ieee80211_mgmt_frame_register,
.set_antenna = ieee80211_set_antenna,
.get_antenna = ieee80211_get_antenna,
.set_ringparam = ieee80211_set_ringparam,
.get_ringparam = ieee80211_get_ringparam,
};