EM9191 PCIe with CM4

[Vincent ESCARGUEL]

Hi,

I’m using a Sierra EM9191(sdx55) with PCIe on a raspberry CM4.
Until now I had a firmware based on openWRT21.02, for which Aleksander had tuned the MM1.18.2 and few drivers.
It worked nicely but we bought a new lot of CM4 and I need to upgrade few files for it to boot (start4.elf and fixup.dat).
Upgrading the gpu-firmware package of the bcm2711 did the trick but it seems to have a side effect because the modem can’t connect properly anymore.
For every new attempt (through luci) it attach, register and fail to connect, leaving the modem in a disabled state.

My first move was to try the ‘official’ new openwrt, with latest update and better support to my hardware.
I had the same result with openwrt 23.05/MM1.20.6 and openwrt master/MM1.22

If I delete my interface in luci, then recreate it, sometimes it connects but there is no downlink traffic.

When I try manually to establish the connection, I have this return:
# mmcli -m 0 -e
successfully enabled the modem.
#  mmcli -m 0 --simple-connect="apn="
error: couldn't connect the modem: 'GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Unsupported: Cannot disable multiplex support'

I managed to make the MHI driver handle the modem but I’m struggling with MM, anyone has a clue of what’s going on? 
If you need more information or trace, just let me know.

Best regards,
Vincent