這裏使用的是ath9k網卡驅動，硬件平臺是TP-link TL-WR841N V7.1 路由器
1 ath_pci_init()驅動的主入口爲ath_pci_init()（位於linux-3.3.8 /drivers/net/wireless/ath/ath9k文件夾下的pci.c文件中）：
int ath_pci_init(void)
{
return pci_register_driver(&ath_pci_driver);
}static struct pci_driver ath_pci_driver = {
.name = "ath9k",
.id_table = ath_pci_id_table,
.probe = ath_pci_probe,
.remove = ath_pci_remove,
.driver.pm = ATH9K_PM_OPS,
};
2 ath_pci_probe() 緊接着，系統會通過probe指針來調用ath_pci_probe函數（ath_pci_probe函數定義於linux-3.3.8 /drivers/net/wireless/ath/ath9k文件夾下的pci.c文件中）。
static int ath_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
{
…
hw = ieee80211_alloc_hw(sizeof(struct ath_softc), &ath9k_ops);
if (!hw) {
dev_err(&pdev->dev, "No memory for ieee80211_hw\n");
ret = -ENOMEM;
goto err_alloc_hw;
}
SET_IEEE80211_DEV(hw, &pdev->dev);
pci_set_drvdata(pdev, hw);
sc = hw->priv;
sc->hw = hw;
sc->dev = &pdev->dev;
sc->mem = mem;
/* Will be cleared in ath9k_start() */
sc->sc_flags |= SC_OP_INVALID;
ret = request_irq(pdev->irq, ath_isr, IRQF_SHARED, "ath9k", sc);
if (ret) {
dev_err(&pdev->dev, "request_irq failed\n");
goto err_irq;
}
sc->irq = pdev->irq;
ret = ath9k_init_device(id->device, sc, &ath_pci_bus_ops);
if (ret) {
dev_err(&pdev->dev, "Failed to initialize device\n");
goto err_init;
}
…
}
3 ieee80211_alloc_hw() 注意ath_pci_probe()函數體中的這行代碼:
hw = ieee80211_alloc_hw(sizeof(struct ath_softc), &ath9k_ops);
函數ieee80211_alloc_hw()定義於OpenWRT內核文件夾子目錄/net/mac80211，文件main.c中，這裏傳入的參數是結構體ath9k_ops, 該結構體的定義如下（位於linux-3.3.8 /drivers/net/wireless/ath/ath9k文件夾下的main.c文件中）:
struct ieee80211_ops ath9k_ops = {
.tx = ath9k_tx,
.start = ath9k_start,
.stop = ath9k_stop,
.add_interface = ath9k_add_interface,
.change_interface = ath9k_change_interface,
.remove_interface = ath9k_remove_interface,
.config = ath9k_config,
.configure_filter = ath9k_configure_filter,
.sta_add = ath9k_sta_add,
.sta_remove = ath9k_sta_remove,
.sta_notify = ath9k_sta_notify,
.conf_tx = ath9k_conf_tx,
.bss_info_changed = ath9k_bss_info_changed,
.set_key = ath9k_set_key,
.get_tsf = ath9k_get_tsf,
.set_tsf = ath9k_set_tsf,
.reset_tsf = ath9k_reset_tsf,
.ampdu_action = ath9k_ampdu_action,
.get_survey = ath9k_get_survey,
.rfkill_poll = ath9k_rfkill_poll_state,
.set_coverage_class = ath9k_set_coverage_class,
.flush = ath9k_flush,
.tx_frames_pending = ath9k_tx_frames_pending,
.tx_last_beacon = ath9k_tx_last_beacon,
.get_stats = ath9k_get_stats,
.set_antenna = ath9k_set_antenna,
.get_antenna = ath9k_get_antenna,
};
將參數ath9k_ops傳輸ieee80211_alloc_hw()函數以後，系統將可以使用參數ath9k_ops中定義的函數指針。以tx爲例，在tx.c中將會用到該函數指針。 下面再來看看ieee80211_alloc_hw()函數：
struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len, const struct ieee80211_ops *ops)
{
struct ieee80211_local *local;
int priv_size, i;
struct wiphy *wiphy;
bool use_chanctx;
…
/* 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 |
* +-------------------------+
*
*/
priv_size = ALIGN(sizeof(*local), NETDEV_ALIGN) + priv_data_len;
// 注意這裏的mac80211_config_ops
// 以其中的scan成員爲例，scan時就會觸發對應的函數ieee80211_scan()
wiphy = wiphy_new(&mac80211_config_ops, priv_size); // 注意這裏的mac80211_config_ops
if (!wiphy)
return NULL;
…
// 這裏的local->ops就變成傳進來的參數ath9k_ops
local->ops = ops;
…
// 這個工作隊列很重要, sw scan的情況下會schedule這個工作隊列來做scan
INIT_DELAYED_WORK(&local->scan_work, ieee80211_scan_work);
…
// 這個tasklet跟接受數據緊密相關，後面會提到
tasklet_init(&local->tasklet,
ieee80211_tasklet_handler,
(unsigned long) local);
…
return &local->hw;
}
EXPORT_SYMBOL(ieee80211_alloc_hw);
4 ath9k_init_device() 在ath_pci_probe()的函數體中，完成了ieee80211_alloc_hw()之後的另一行重要代碼就是：
ret = ath9k_init_device(id->device, sc, &ath_pci_bus_ops);
接着分析ath9k_init_device ()（位於OpenWRT內核文件夾子目錄/net/mac80211，文件init.c中），觀察設備的初始化過程。
int ath9k_init_device(u16 devid, struct ath_softc *sc, const struct ath_bus_ops *bus_ops)
{
struct ieee80211_hw *hw = sc->hw;
struct ath_common *common;
struct ath_hw *ah;
int error = 0;
struct ath_regulatory *reg;
/* Bring up device */
error = ath9k_init_softc(devid, sc, bus_ops);
if (error != 0)
goto error_init;
ah = sc->sc_ah;
common = ath9k_hw_common(ah);
ath9k_set_hw_capab(sc, hw);
/* Initialize regulatory */
error = ath_regd_init(&common->regulatory, sc->hw->wiphy,
ath9k_reg_notifier);
if (error)
goto error_regd;
reg = &common->regulatory;
/* Setup TX DMA */
error = ath_tx_init(sc, ATH_TXBUF);
if (error != 0)
goto error_tx;
/* Setup RX DMA */
error = ath_rx_init(sc, ATH_RXBUF);
if (error != 0)
goto error_rx;
ath9k_init_txpower_limits(sc);
…
error = ieee80211_register_hw(hw);
if (error)
goto error_register;
error = ath9k_init_debug(ah);
if (error) {
ath_err(common, "Unable to create debugfs files\n");
goto error_world;
}
…
}
4.1 首先初始化softc static int ath9k_init_softc(u16 devid, struct ath_softc *sc,
const struct ath_bus_ops *bus_ops)
{
…
tasklet_init(&sc->intr_tq, ath9k_tasklet, (unsigned long)sc);
tasklet_init(&sc->bcon_tasklet, ath_beacon_tasklet,
(unsigned long)sc);
…
}4.2 初始化數據收發存儲器訪問
/* Setup TX DMA */
error = ath_tx_init(sc, ATH_TXBUF);
if (error != 0)
goto error_tx;
/* Setup RX DMA */
error = ath_rx_init(sc, ATH_RXBUF);
if (error != 0)
goto error_rx;error = ieee80211_register_hw(hw);
至此，設備啓動，驅動程序成功加載到設備上。