Messages in this thread | | | Subject | Re: [PATCH] USB: serial: option: set driver_info for SIM5218 and compatibles | From | Dan Williams <> | Date | Tue, 19 Mar 2019 09:30:25 -0500 |
| |
On Tue, 2019-03-19 at 13:43 +0100, Johan Hovold wrote: > On Tue, Mar 19, 2019 at 01:27:19PM +0100, Johan Hovold wrote: > > On Tue, Mar 19, 2019 at 12:25:53PM +0000, Måns Rullgård wrote: > > > Johan Hovold <johan@kernel.org> writes: > > > > > > > On Tue, Mar 19, 2019 at 10:54:00AM +0000, Måns Rullgård wrote: > > > > > Johan Hovold <johan@kernel.org> writes: > > > > > > > Regardless, setting the NCTRL flag should be harmless. > > > > > > > > > > > > Well, there are devices that depend on getting these > > > > > > requests, at least > > > > > > for the QMI interface. But we can always revert if anyone > > > > > > complains. > > > > > > > > > > The QMI interface doesn't even pretend to be a uart. The > > > > > other ones do, > > > > > but there isn't actually any real uart behind them. For > > > > > instance, it > > > > > doesn't matter what baud rate one sets. > > > > > > > > Sure, but some devices still require "DTR" to be set for the > > > > QMI > > > > interface, so there not being any real uart is no guarantee > > > > that there > > > > is no firmware that expects these calls. > > > > > > Now I'm thoroughly confused. The QMI interface has a completely > > > separate driver that creates a network device (if I'm reading the > > > code > > > correctly). > > > > I was just giving an example of firmware sometimes doing unexpected > > things. > > See 93725149794d ("net: qmi_wwan: MDM9x30 specific power management") > for some background.
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.
Dan
| |