Hi, On an imx7d-based board running kernel 5.10.158, I noticed that a Quectel BG96 modem is gone after sending a reset command via AT: # microcom /dev/ttyUSB3 >AT+CFUN=1,1 OK usb 2-1: USB disconnect, device number 6 option1 ttyUSB0: GSM modem (1-port) converter now disconnected from ttyUSB0 option 2-1:1.0: device disconnected option1 ttyUSB1: GSM modem (1-port) converter now disconnected from ttyUSB1 option 2-1:1.1: device disconnected option1 ttyUSB2: GSM modem (1-port) converter now disconnected from ttyUSB2 option 2-1:1.2: device disconnected option1 ttyUSB3: GSM modem (1-port) converter now disconnected from ttyUSB3 option 2-1:1.3: device disconnected qmi_wwan 2-1:1.4 wwan0: unregister 'qmi_wwan' usb-ci_hdrc.1-1, WWAN/QMI device # lsusb Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub The USB modem is gone. Forcing an 'echo on' to power/control makes the USB modem reappear: # echo 'on' > /sys/bus/usb/devices/usb2/power/control usb 2-1: new high-speed USB device number 7 using ci_hdrc usb 2-1: New USB device found, idVendor=2c7c, idProduct=0296, bcdDevice= 0.00 usb 2-1: New USB device strings: Mfr=3, Product=2, SerialNumber=4 usb 2-1: Product: Qualcomm CDMA Technologies MSM usb 2-1: Manufacturer: Qualcomm, Incorporated usb 2-1: SerialNumber: 7d1563c1 option 2-1:1.0: GSM modem (1-port) converter detected usb 2-1: GSM modem (1-port) converter now attached to ttyUSB0 option 2-1:1.1: GSM modem (1-port) converter detected usb 2-1: GSM modem (1-port) converter now attached to ttyUSB1 option 2-1:1.2: GSM modem (1-port) converter detected usb 2-1: GSM modem (1-port) converter now attached to ttyUSB2 option 2-1:1.3: GSM modem (1-port) converter detected usb 2-1: GSM modem (1-port) converter now attached to ttyUSB3 qmi_wwan 2-1:1.4: cdc-wdm0: USB WDM device qmi_wwan 2-1:1.4 wwan0: register 'qmi_wwan' at usb-ci_hdrc.1-1, WWAN/QMI device, 12:bc:8c:zz:yy:xx # lsusb Bus 002 Device 007: ID 2c7c:0296 Quectel Wireless Solutions Co., Ltd. BG96 CAT-M1/NB-IoT modem Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Sending the AT reset command afterward works fine, and the modem keeps connected. Previously, this board used a vendor-based 4.14 kernel and such a problem did not happen. Kernels 5.10 and 4.14 have the same 'auto' option selected by default. Also tested kernel 6.1 and it behaves the same as 5.10.158. What can be done so that the reset modem command does not cause the modem to disappear by default? Thanks, Fabio Estevam
