On a PS4, I have a ps4 controller as the donor controller connected to A1 and connect my 2nd ps4 controller via wireless using the P2 button.
I just loaded up Gran Turismo Sport to test, the game seems to respond to both the donor and the active controllers accelerometer input, is this usual? This makes it awkward to control as any movement on the donor controller interferes with the main wireless controller.
It actually makes the game unplayable using accelerometer input, as the zero point is constantly shifting, the passthrough controller needs constantly moving to a new rotation to provide zero input.