rtl8821CS

在 drivers/net/wireless/realtek/rtl8821/Kconfig 中，调整 help 字段以匹配 Luban 的解析格式：

config RTL8821CS
    tristate "Realtek 8821C SDIO WiFi"
-    ---help---
+       help

大部分 WiFi 驱动为了增强兼容性，驱动中会有一些存放 .h 文件的目录，在 Makefile 中进行引用。因为版本的差异， 此类目录的引用方法可能不一样，从而导致出错。以下为一种报错的示例及解决方法：

在 menuconfig 功能配置界面，进行如下功能配置：

1. 无线配置

   如需使用 WiFi ，必须要在 Kernel 中打开 cfg80211 和 mac80211 的支持：

   Networking support > Wireless
   
   --- Wireless
   <*>   cfg80211 - wireless configuration API
   [ ]     nl80211 testmode command (NEW)
   [ ]     enable developer warnings (NEW)
   [ ]     cfg80211 certification onus (NEW)
   [*]     enable powersave by default(NEW)
   [ ]     cfg80211 DebugFS entries (NEW)
   [*]     support CRDA (NEW)
   [*]     cfg80211 wireless extensions compatibility
   <*>   Generic IEEE 802.11 Networking Stack (mac80211)
   [*]   Minstrel (NEW)
         Default rate control algorithm (Minstrel)  --->
   [ ]   Enable mac80211 mesh networking support (NEW)
   [ ]   Export mac80211 internals in DebugFS (NEW)
   [ ]   Trace all mac80211 debug messages (NEW)
   [ ]   Select mac80211 debugging features (NEW)
   

2. 蓝牙配置

   BT 的使用必须要在 Kernel 中打开 bluetooth 子系统相关配置：

   Networking support > Bluetooth subsystem support > Bluetooth device drivers
   
   < > HCI USB driver
   < > HCI SDIO driver
   <*> HCI UART driver
   [*]   UART (H4) protocol support
   < >   UART Nokia H4+ protocol support
   [ ]   BCSP protocol support
   [ ]   Atheros AR300x serial support
   [ ] HCILL protocol support
   -*- Three-wire UART (H5) protocol support
   [ ] Intel protocol support
   [ ] Broadcom protocol support
   [*] Realtek protocol support
   [ ] Qualcomm Atheros protocol support
   [ ] Intel AG6XX protocol support
   [ ] Marvell protocol support
   < > HCI BCM203x USB driver
   < > HCI BPA10x USB driver
   < > HCI BlueFRITZ! USB driver
   < > HCI VHCI (Virtual HCI device) driver
   < > Marvell Bluetooth driver support
   < > MediaTek HCI SDIO driver
   < > MediaTek HCI UART driver
   

3. RFKILL 配置

   RFKILL 的使用必须要在 Kernel 中打开相关配置

   Networking support > RF switch subsystem support
   
    --- RF switch subsystem support
    [ ]   RF switch input support
    <*>   GPIO RFKILL driver
   

4. 驱动选择

   要使用 8821C 驱动，需要在 Kernel 中打开该驱动

   Device Drivers > Network device support > Wireless LAN
   
   [*]   Realtek devices
   < >     Realtek 8187 and 8187B USB support
   < >     Realtek rtlwifi family of devices  ----
   < >     RTL8723AU/RTL8188[CR]U/RTL819[12]CU (mac80211) support
   < >     Realtek 802.11ac wireless chips support  ----
   <*>     Realtek 8821C SDIO WiFi
   

在 board.dts 中配置各个子节点：

1. WIFI
   1. 打开对应的 SDMC：

      &sdmc1 {
          pinctrl-names = "default";
          pinctrl-0 = <&sdmc1_pins_a>;//核对引脚是否和原理图一致
          bus-width = <4>;
          no-mmc;
          no-sd;
          non-removalbe;
          cap-sdio-irq;
          status = "okay";
      };

   2. 配置控制引脚：

      rfkill_wlan {
          compatible = "rfkill-gpio";
          rfkill-name = "wlan";
          rfkill-type = <1>;
          reset-gpios = <&gpio_e 4 GPIO_ACTIVE_HIGH>;//模组 WiFi 使能引脚，根据实际原理图配置
          shutdown-gpios = <&gpio_d 8 GPIO_ACTIVE_LOW>;//电源控制引脚，根据实际原理图配置
          status = "okay";
      };

2. BT
   1. 打开对应 UART：

      &uart6 {
          pinctrl-names = "default";
          pinctrl-0 = <&uart6_pins_a>, <&uart6_rts_pins_a>, <&uart6_rts_pins_b>;//须和原理图保持一致
         status = "okay";
      };

   2. 配置控制引脚：

      rfkill_bt {
          compatible = "rfkill-gpio";
          rfkill-name = "bluetooth";
          rfkill-type = <2>;
          reset-gpios = <&gpio_c 6 GPIO_ACTIVE_HIGH>;//模组蓝牙使能引脚，须和原理图保持一致
          status = "okay";
      };

蓝牙固件和下载工具，可以从模组厂获取，存放于 overylay 目录。目录结构如下所示：

├── lib
│   └── firmware
│       └── rtlbt
│           ├── rtl8821c_config//模组配置文件，最好从模组厂获取
│           └── rtl8821c_fw//模组固件，最好从模组厂获取
├── usr
│   └── bin
│       └── rtk_hciattach//模组蓝牙固件下载工具，最好从模组厂获取