Re: [PATCH] USB: serial: option: set driver_info for SIM5218 and compatibles

From: Måns Rullgård
Date: Tue Mar 19 2019 - 12:26:43 EST

Bjørn Mork <bjorn@xxxxxxx> writes:

> Måns Rullgård <mans@xxxxxxxxx> writes:
>> Dan Williams <dcbw@xxxxxxxxxx> writes:
>>> TLDR; some firmware uses the DTR signal as an indicator to come out of
>>> low-power mode. Without doing so you cannot talk to the modem over any
>>> of it's ports, QMI, net, or serial.
>> I must be missing something, but how does a network interface have a DTR
>> signal?
> It does not. But the network function is (ab)using the Comm class USB
> control message "SetControlLineState" to signal "wake up" from the host
> to the device. Which is perfectly fine since the USB function in
> question is vendor specific. The vendor can define any USB control
> message to mean anything they want. Reusing a Comm class message
> probably made sense to the firmware engineer designing this. We can
> only note and adapt.
> It doesn't have anything to do with DTR.

Every time you think USB can't get any worse, it does.

Måns Rullgård