More info from the tech team:
The XPS 13 9343 utilizes the Microsoft Precision Touchpad specification in I2C mode. The specific feature within the Microsoft Precision Touchpad specification is the “Confidence” feature:
Confidence is used to indicate that the contact does not have any dimensions (height or width) > 25mm that implies that it is not an unintended contact. Windows Precision Touchpads should not reject any contacts in firmware processing, but should forward all contacts to the host and indicate the confidence. After a device has deemed a contact to be unintentional, it shall clear the confidence bit for that contact report and all subsequent reports. Until a contact has been deemed unintentional, the device shall set the confidence bit for that contact being reported.
With that feature correctly implemented, palm rejection in I2C mode should work.
Driver feature development is something we work with our vendors on ensuring they develop, though in this case they won’t since the Microsoft Precision Touchpad specification is a feature that falls outside of vendor-specific needs. Synaptics (or any other touchpad vendor) is unlikely to implement this feature in the Linux i2c_hid driver because it’s not vendor-specific but instead a Microsoft specification.
Microsoft Precision Touchpad specification:
Pau for now…