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Option is likely the right driver for this device.
qcaux was mainly for mobile phones that have a TTY (often cdc-acm) as the modem port and a secondary DIAG/DM port driven by qcaux. The DM port doesn't have an interrupt endpoint thus it's not a normal modem port requiring the larger buffers of option and its control signaling.
qcserial (as Bjorn mentioned) is only for actual Gobi-type devices with the specific layouts and the firmware loading requirement where the 1K and 2K devices start in a special 1-port mode waiting for firmware and then become 4-port devices on firmware reboot.
Dan
Thank you all. I believe that many people are confused in selecting serial driver (option and qcserial) for QUALCOMM based module. This thread has provided clearly and properly presented the different between them.
SZ