当前使用的Linux内核版本： 4.4.189
插上USB Bluetooth 5.0 Adapter后，dmesg显示如下log:
[ 240.348480] usb 3-1.2: new full-speed USB device number 6 using ehci-platform
[ 240.437834] usb 3-1.2: New USB device found, idVendor=0bda, idProduct=8771
[ 240.438541] usb 3-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 240.439311] usb 3-1.2: Product: Bluetooth Radio
[ 240.439730] usb 3-1.2: Manufacturer: Realtek
[ 240.440124] usb 3-1.2: SerialNumber: 00E04C239987
[ 240.447374] Bluetooth: hci0: rtl: examining hci_ver=0a hci_rev=000b lmp_ver=0a lmp_subver=8761
[ 240.448393] Bluetooth: hci0: rtl: loading rtl_bt/rtl8761a_fw.bin
[ 240.451607] Bluetooth: hci0: rom_version status=0 version=1
[ 242.616194] Bluetooth: hci0 command 0xfc20 tx timeout
[ 250.612377] Bluetooth: hci0: download fw command failed (-110)由于蓝牙适配器的芯片组较新，为Realtek RTL8761B，4.4版本的内核并不支持这个型号的蓝牙适配器，所以驱动报错。
解决办法：
1. 把较高内核版本的驱动移植到4.4.189上来：
这里我们选择 kernel4.17.19 版本的驱动，可以从这个仓库获取驱动源码： https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
Realtek USB bluetooth适配器的驱动文件为：
- drivers/bluetooth/btrtl.h
- drivers/bluetooth/btrtl.c
用上述btrtl.c和btrtl.h替换掉 kernel4.4.189 版本里对应的文件。
注意：这里也可以移植更高内核版本的驱动，比如 kernel5.4 版本的驱动。但是有个缺点，选择的驱动版本的跨度越大需要修改的地方就越多。
2. 修改4.17.19内核版本Realtek bluetooth驱动源码：
修改 drivers/bluetooth/btrtl.c 和 drivers/bluetooth/btrtl.h
这里我做了一个修改后的patch：support_RTL8761B_chipset_from_kernel4.4_to_kernel4.17.patch， patch内容如下：
diff --git a/kernel/drivers/bluetooth/btrtl.c b/kernel/drivers/bluetooth/btrtl.c
index 437f080..bd00d25 100644
--- a/kernel/drivers/bluetooth/btrtl.c
+++ b/kernel/drivers/bluetooth/btrtl.c
@@ -32,7 +32,7 @@
#define RTL_ROM_LMP_8723A 0x1200
#define RTL_ROM_LMP_8723B 0x8723
#define RTL_ROM_LMP_8821A 0x8821
-#define RTL_ROM_LMP_8761A 0x8761
+#define RTL_ROM_LMP_8761B 0x8761
#define RTL_ROM_LMP_8822B 0x8822
#define IC_MATCH_FL_LMPSUBV (1 << 0)
@@ -76,11 +76,11 @@ static const struct id_table ic_id_table[] = {
.fw_name = "rtl_bt/rtl8821c_fw.bin",
.cfg_name = "rtl_bt/rtl8821c_config.bin" },
- /* 8761A */
- { IC_MATCH_FL_LMPSUBV, RTL_ROM_LMP_8761A, 0x0,
+ /* 8761B */
+ { IC_MATCH_FL_LMPSUBV, RTL_ROM_LMP_8761B, 0x0,
.config_needed = false,
- .fw_name = "rtl_bt/rtl8761a_fw.bin",
- .cfg_name = "rtl_bt/rtl8761a_config.bin" },
+ .fw_name = "rtl_bt/rtl8761b_fw.bin",
+ .cfg_name = "rtl_bt/rtl8761b_config.bin" },
/* 8822B */
{ IC_INFO(RTL_ROM_LMP_8822B, 0xb),
@@ -140,10 +140,10 @@ static int rtlbt_parse_firmware(struct hci_dev *hdev, u16 lmp_subver,
{ RTL_ROM_LMP_8723A, 0 },
{ RTL_ROM_LMP_8723B, 1 },
{ RTL_ROM_LMP_8821A, 2 },
- { RTL_ROM_LMP_8761A, 3 },
{ RTL_ROM_LMP_8822B, 8 },
{ RTL_ROM_LMP_8723B, 9 }, /* 8723D */
{ RTL_ROM_LMP_8821A, 10 }, /* 8821C */
+ { RTL_ROM_LMP_8761B, 14 }, /* 8761BU */
};
ret = rtl_read_rom_version(hdev, &rom_version);
@@ -514,7 +514,7 @@ int btrtl_setup_realtek(struct hci_dev *hdev)
return btrtl_setup_rtl8723a(hdev);
case RTL_ROM_LMP_8723B:
case RTL_ROM_LMP_8821A:
- case RTL_ROM_LMP_8761A:
+ case RTL_ROM_LMP_8761B:
case RTL_ROM_LMP_8822B:
return btrtl_setup_rtl8723b(hdev, hci_rev, lmp_subver);
default:内核编译选项：
重新编译内核和更新内核，内核重新启动后，插入RTL8761B chipset蓝牙适配器，dmesg打印log如下：
[ 13.340498] usb 4-1.2: new full-speed USB device number 4 using ehci-platform
[ 13.428053] usb 4-1.2: New USB device found, idVendor=0bda, idProduct=8771
[ 13.428738] usb 4-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 13.429457] usb 4-1.2: Product: Bluetooth Radio
[ 13.429875] usb 4-1.2: Manufacturer: Realtek
[ 13.430296] usb 4-1.2: SerialNumber: 00E04C239987
[ 13.437530] Bluetooth: hci1: rtl: examining hci_ver=0a hci_rev=000b lmp_ver=0a lmp_subver=8761
[ 13.438361] Bluetooth: hci1: rtl: loading rtl_bt/rtl8761b_config.bin
[ 13.441437] Bluetooth: hci1: rtl: loading rtl_bt/rtl8761b_fw.bin
[ 13.443434] Bluetooth: hci1: rom_version status=0 version=1
[ 13.444009] Bluetooth: hci1: cfg_sz 14, total size 11678上述使用的固件版本rtl8761b_config.bin和rtl8761b_fw.bin可以用此仓库获得： git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git ，或者从ubuntu20.04(kernel版本>= 5.4)的/lib/firmware/rtl_bt/目录下拷贝来直接用。
如果bluetoothd程序已经启动了的话，执行 hciconfig 结果如下：
# hciconfig
hci0: Type: Primary Bus: USB
BD Address: E8:EA:6A:8C:20:ED ACL MTU: 1021:6 SCO MTU: 255:12
UP RUNNING
RX bytes:12651 acl:0 sco:0 events:414 errors:0
TX bytes:14146 acl:0 sco:0 commands:101 errors:0执行 bluetoothctl scan on 进行扫描，结果如下：
# bluetoothctl scan on
Discovery started
[CHG] Controller E8:EA:6A:8C:20:ED Discovering: yes
[NEW] Device 52:FB:49:66:89:C0 52-FB-49-66-89-C0
[NEW] Device 4D:A3:E2:E0:D1:8A 4D-A3-E2-E0-D1-8A
[NEW] Device 5C:73:91:E3:7C:23 5C-73-91-E3-7C-23
[NEW] Device 7A:AC:FF:A1:12:49 7A-AC-FF-A1-12-49
[NEW] Device 52:EE:DB:DF:78:F1 52-EE-DB-DF-78-F1
[NEW] Device 67:6A:97:56:84:F2 67-6A-97-56-84-F2
[NEW] Device 42:B8:EB:55:82:D8 42-B8-EB-55-82-D8
[NEW] Device C8:28:32:8F:C9:96 C8-28-32-8F-C9-96
[NEW] Device 50:B3:3E:9A:94:2E 50-B3-3E-9A-94-2E
[NEW] Device 63:E1:C1:03:78:FB 63-E1-C1-03-78-FB
[NEW] Device 63:B5:8F:19:01:3E 63-B5-8F-19-01-3E
[NEW] Device 63:7E:AA:D0:47:1E 63-7E-AA-D0-47-1E
[NEW] Device 46:3C:37:25:5E:EE 46-3C-37-25-5E-EE
[NEW] Device 44:28:A3:BE:B3:A1 MI RC
[NEW] Device 47:C0:B7:D4:A8:9F 47-C0-B7-D4-A8-9F
[NEW] Device 70:28:24:F1:24:7B 70-28-24-F1-24-7B
[NEW] Device 63:F8:74:A3:4A:39 63-F8-74-A3-4A-39
[NEW] Device 5B:6E:56:B5:4F:F1 5B-6E-56-B5-4F-F1
[NEW] Device 47:B7:9C:97:E0:30 47-B7-9C-97-E0-30
[NEW] Device 4D:94:FC:E5:F8:29 4D-94-FC-E5-F8-29
[NEW] Device 68:94:22:61:95:9D 68-94-22-61-95-9D
[NEW] Device 78:35:4A:C5:99:2A 78-35-4A-C5-99-2A从上面的扫描结果来看，蓝牙适配器已经能正常工作了。
至此，从kernel4.4到kernel.4.17版本的内核，都可以使用上述修改过的驱动来支持RTL8761B芯片组的蓝牙适配器。