Public bug reported:

**Problem description**

The integrated Fibocom L860-GL (Intel XMM7560) LTE modem in my Lenovo
ThinkPad P15 Gen 1 works under Windows 11 Pro but fails to initialize
under Linux Mint 22.1 Cinnamon.

The Linux kernel detects the PCIe modem and binds the `iosm` driver.
WWAN device nodes are created, but ModemManager cannot initialize the
modem.

**System information**

- Laptop: Lenovo ThinkPad P15 Gen 1
- OS: Linux Mint 22.1 Cinnamon (Ubuntu-based)
- Tested kernels: 6.8.0-146-generic and 7.0.0-38-generic
- BIOS: N30ET54W (1.37)
- Modem: Fibocom L860-GL / Intel XMM7560
- PCI ID: 8086:7560
- Subsystem ID: 1cf8:8601
- Kernel driver: iosm
- ModemManager: 1.23.4
- Modem firmware: 18600.5001.00.35.01.57 (obtained under Windows)

**Kernel error**

```
iosm 0000:53:00.0: ch[6]: confused phase 3
```

**ModemManager messages**

```
creating modem with plugin 'Intel' and '4' ports
modem ... successfully created
couldn't start initialization: Transaction timed out
fatal error initializing: Fatal error: modem is unusable
```

**WWAN device nodes**

```
/dev/wwan0at0
/dev/wwan0at1
/dev/wwan0mbim0
```

**Diagnostics performed**

- `mmcli -L` returns `No modems were found`.
- Direct MBIM access fails with an input/output error, including when 
ModemManager is stopped.
- Opening the AT interface fails with an input/output error.
- No active rfkill block was present when checked.
- The PCIe device remains bound to `iosm`.
- No PCIe fatal or non-fatal AER errors were recorded.
- The issue persists with both tested kernels.
- Rebooting from Windows into Linux with Windows mobile broadband enabled or 
disabled did not resolve the issue.

**Expected result**

ModemManager should successfully initialize the integrated LTE modem and
make it available for mobile broadband connections.

**Actual result**

Modem initialization times out, and the modem is reported as unusable.

**Request**

Could the kernel maintainers investigate whether this is a known `iosm`
driver issue affecting Intel XMM7560 devices?

Please advise whether a fix or patch is available and which additional
diagnostic logs would be useful.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "PCI device identification and kernel driver information 
for the integrated Fibocom L860-GL (Intel XMM7560) LTE modem."
   
https://bugs.launchpad.net/bugs/2171011/+attachment/6009515/+files/fibocom-lte.log

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https://bugs.launchpad.net/bugs/2171011

Title:
  Fibocom L860-GL (Intel XMM7560): iosm "confused phase 3", modem
  initialization times out

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