Hello again,
I would like to add a sensor to I2C line and according to 4DPi-24HAT specification this bus is used by touchscreen controller. As far as I know I2C this shall be not a big deal to add another slave device on the bus. Hence I have some questions:

1. What is "bus load" made by the touchscreen controller? I do not have any osciloscope to check it
2. Shall I use extra pull up? I guess touch screen already pulls SDA line up. I expect that wire will have 20-50cm.
3. Are there any limiations in regards to I2C with your kernel?

1. First question stays.
2. I added extra pullup and it is working fine - I did not try without it.
3. Third question stays as well.