How do I disable I2C Designware support when it's not built as a module?

After reading kernel sources, I found a function we need to blacklist!

Thanks to Stephen Kitt for the hint about initcall_blacklist.

Add initcall_blacklist=dw_i2c_init_driver to the kernel command line. This works for me on kernel 4.15.0.

For anyone else who'll find this answer. You can do it by editing /etc/default/grub:

1. Run in the terminal: sudo -H gedit /etc/default/grub.
2. Append blacklist string to the GRUB_CMDLINE_LINUX_DEFAULT: GRUB_CMDLINE_LINUX_DEFAULT="… initcall_blacklist=dw_i2c_init_driver".
3. Save the file, close the editor.
4. Run in the terminal: sudo update-grub.
5. Reboot and test!

Adding initcall_blacklist=i2c_dw_init_master to the kernel command-line should stop the Designware driver from initialising during boot, and avoid the issue altogether.

See the kernel parameters for a very brief description of initcall_blacklist, and the thread around the patch for more useful background information.