On my Lenovo ThinkPad L13 Yoga Gen 2 AMD, the hotkey_gmms_get_tablet_mode function in thinkpad_acpi module shows the following warning in dmesg: Unknown/reserved multi mode value 0x0000 for type 4, please report this to ibm-acpi-devel@lists.sourceforge.net Furthermore, tablet mode detection does not work at all. Since I have the hardware here and want it to work, let me know if I can provide any more information or test a patch.
Update: I spent the last day or so inserting printk statements at various points throughout the driver, as well as using acpica to see if/when the hotkey logic in the driver runs. As far as I can tell, this devices' tablet switch does not get recognized at all by the driver, turning the screen around does not trigger anything in the driver. There are no calls to acpi_evalf, the hotkey_notify function does not recognize the event, and I can't see any ACPI_EVENTS through /sys/module/acpi/debug_layer. hotkey_gmms_get_tablet_mode only gets run on boot, resume or when reading /sys/bus/platform/devices/thinkpad_acpi/hotkey_tablet_mode. I have Windows 11 installed on the same machine, it works perfectly there. I identified the driver that handles tablet mode is called "Microsoft HID GPIO Laptop or Slate Indicator Driver". If needed, I can provide the information it exposes via device manager. If I can help in any way, please let me know.
I have seen the same message "thinkpad_acpi: Unknown/reserved multi mode value 0x0000 for type 4, please report this to ibm-acpi-devel@lists.sourceforge.net" on RedHat 9.0 5.14.0-70.22.1.el9_0.x86_64 running on a ThinkPad E15, Gen2, but havent seen any issues whatsoever