将 usb 角色从主机切换到小工具在 Linux 上不起作用

Question

我在基于 i.MX6 处理器的定制板上运行 Linux。 USB 端口的设备树配置为 otg，两个角色是工作小工具（

g_ether

或

g_serial

）和主机（插入大容量存储设备）。启动后 USB 配置为小工具，在这种情况下，我可以加载

g_ether

并与我的笔记本电脑毫无问题地通信。之后，我将角色切换为主持人，就像之前一样工作正常。我可以将“大容量存储”连接到电路板，系统可以识别它。最后，当我再次将角色切换回 gadget 时，我无法再使

g_ether

或

g_serial

工作。

dmesg

上没有错误信息。

设备树

&usbotg1 {
    pinctrl-names = "default";
    dr_mode = "otg";
    status = "okay";
};

Linux

root@xxxx:~# uname -a
Linux xxxx 5.4.24-2.0.0+g8115d570b280 #1 SMP PREEMPT Tue Sep 21 14:56:23 UTC 2021 armv7l armv7l armv7l GNU/Linux

硬件

1. The board has a mini USB-B female connector
2. The ID pin is connected to ground
3. The +5V is not used (not connected)

重现问题的分步命令

### 1. After boot the default role is gadget
root@xxxx:~# cat /sys/kernel/debug/ci_hdrc.0/role                                                                                                             
gadget

### 2. Plug laptop and confirm that g_ether is working
root@xxxx:~# ifconfig usb0                                                                                                                                 
usb0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500  metric 1
        inet 192.168.7.1  netmask 255.255.255.0  broadcast 192.168.7.255
        inet6 fe80::64ba:c3ff:fef0:cfba  prefixlen 64  scopeid 0x20<link>
        ether 66:ba:c3:f0:cf:ba  txqueuelen 1000  (Ethernet)
        RX packets 62  bytes 6802 (6.6 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 45  bytes 3754 (3.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

root@xxxx:~# ping -c 2 -w 3 192.168.7.3                                                                                                                            
PING 192.168.7.3 (192.168.7.3): 56 data bytes
64 bytes from 192.168.7.3: seq=0 ttl=64 time=1.161 ms
64 bytes from 192.168.7.3: seq=1 ttl=64 time=1.023 ms

--- 192.168.7.3 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 1.023/1.092/1.161 ms

### 3. Unplug laptop, switch USB role to host and plug mass storage device
root@xxxx:~# echo host > /sys/kernel/debug/ci_hdrc.0/role
root@xxxx:~# cat /sys/kernel/debug/ci_hdrc.0/role
host

root@xxxx:~# dmesg
...
[ 1387.750491] usb 2-1: new high-speed USB device number 3 using ci_hdrc
[ 1387.802654] usb 2-1: New USB device found, idVendor=0525, idProduct=a4a5, bcdDevice= 2.21
[ 1387.802711] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 1387.802745] usb 2-1: Product: USB download gadget
[ 1387.802777] usb 2-1: Manufacturer: FSL
[ 1387.815591] usb-storage 2-1:1.0: USB Mass Storage device detected
[ 1387.837391] usb-storage 2-1:1.0: Quirks match for vid 0525 pid a4a5: 10000
[ 1387.838126] scsi host0: usb-storage 2-1:1.0
[ 1389.031295] usb 2-1: reset high-speed USB device number 3 using ci_hdrc
[ 1389.271363] usb 2-1: reset high-speed USB device number 3 using ci_hdrc
[ 1389.511572] usb 2-1: reset high-speed USB device number 3 using ci_hdrc
[ 1389.751624] usb 2-1: reset high-speed USB device number 3 using ci_hdrc

# sda is present
root@xxxx:~# lsblk 
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda            8:0    1  7.3G  0 disk 
`-sda1         8:1    1  7.3G  0 part 
mmcblk1      179:0    0  7.3G  0 disk 
`-mmcblk1p1  179:1    0  7.3G  0 part /sysroot
mmcblk1boot0 179:8    0    4M  1 disk 
mmcblk1boot1 179:16   0    4M  1 disk 

### 4. Unplug mass store device, switch USB role to gadget
root@xxxx:~# echo gadget > /sys/kernel/debug/ci_hdrc.0/role                                                                                                        
root@xxxx:~# cat /sys/kernel/debug/ci_hdrc.0/role                                                                                                               
gadget

### 5. Interface is present and g_ether is loaded but can't ping laptop anymore
root@xxxx:~# ifconfig usb0                                                                                                                                     
usb0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500  metric 1
        inet 192.168.7.1  netmask 255.255.255.0  broadcast 192.168.7.255
        ether 2e:40:4e:6a:3b:8c  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

root@xxxx:~# lsmod | grep g_ether
g_ether                16384  0

root@xxxx:~# ping -c 2 -w 3 192.168.7.3 
PING 192.168.7.3 (192.168.7.3): 56 data bytes

--- 192.168.7.3 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss

如果在最后一步 (5.) 之后，我再次切换到主机，它仍然可以正常工作，但小工具将不再工作。换句话说，gadget 只有在重新启动后才能工作，而 host 每次都能工作。在切换到小工具之前，我尝试了不同的顺序。比如先卸载

g_ether

再切换角色。我也试过

g_serial

确认问题与网络接口无关。正如我之前提到的，

dmesg

上没有错误，现在我不知道如何调试这个问题。

对正在发生的事情或如何调试它有什么想法吗？