Add QMI-over-QRTR APDU backend for running on Qualcomm SoCs

[z3ntu]

On modern smartphones the communication happens using the QMI protocol via the QRTR transport to communicate with the modem.

Add support for such devices by wrapping libqrtr-glib and libqmi-glib and using those APIs to provide an APDU backend for lpac.

Fixes #41

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Depends on this libqmi MR which hasn't been merged yet: https://gitlab.freedesktop.org/mobile-broadband/libqmi/-/merge_requests/376

[z3ntu]

Do you have a suggestion how to handle the dual-SIM situations, where one wants to set the slot to 1 or 2 (or in theory slot 3 and higher could also exist)?

One idea is adding an environment variable UIM_SLOT=1 to lpac invocation but this wouldn't be nice in my opinion.

[AndySchroder]

I have a Quectel EM120R-GL (https://www.quectel.com/wp-content/uploads/2021/05/Quectel_EM120R-GLEM160R-GL_Hardware_Design_V1.1.pdf), is that device I could test this with? It supports eSIM, and I think it has a Qualcomm chip. It says it supports QMI and QRTR.

[AndySchroder]

If you have multiple modems, how does it know which one to use?

[AndySchroder]

Explain to me the purpose of this feature exactly. We already have ports like /dev/wwan0at1 and /dev/ttyUSB3 for running AT commands on the modem. Can we not just use those ports with at APDU backend?

[z3ntu]

The modems on Qualcomm smartphones don't do AT commands, you communicate with them through QMI.

But for curiosity, does anything show up with qrtr-lookup (from https://github.com/linux-msm/qrtr) with your Quectel modem?

[AndySchroder]

But for curiosity, does anything show up with qrtr-lookup (from https://github.com/linux-msm/qrtr) with your Quectel modem?

Not sure how to get that installed. There aren't any build instructions. I'm running on ubuntu 22.04.

I don't think I'm running a SoC, it's just a cellular radio. Started my troubleshooting of it here though: #73 . I'm thinking I should be able to use both approaches.

[z3ntu]

@AndySchroder git clone https://github.com/linux-msm/qrtr && cd qrtr && meson setup builddir && meson compile -C builddir && ./builddir/src/qrtr-lookup should work, but yeah if it's an external modem then this PR is probably not applicable.

What I know is that some external modems use MBIM so you can check z3ntu/lpac-libqmi-wrapper#1 or even better https://github.com/stich86/lpac-libmbim-wrapper but I don't know any more about eSIM on external modems than that :)

[AndySchroder]

$ ./builddir/src/qrtr-lookup
ERROR qrtr-lookup: sock(AF_QIPCRTR): Address family not supported by protocol
$

[AndySchroder]

The data sheet for the EM120R-GL says QMI/MBIM. Also, mmcli reports drivers: option, cdc_mbim and ports: cdc-wdm0 (mbim), ttyUSB0 (qcdm).