I tried to get the 4 inch display working with my raspberry pi 3 (Waveshare Raspberry Pi 4 Inch Touch Screen TFT LCD(A) 320*480 for Raspberry Pi RPi Model B/Raspberry Pi 2 Model B/Raspberry Pi 3 Model B).
I always had a white screen until I found "Bim"s solution in this question (How to install Waveshare SpotPear 4 inch LCD in RaspberryPI 2?). I followed his answer step for step and it changed the color of the display to black.
What I know now:
the driver is already part of the raspbian kernel so I don't have to install it
I have to copy the waveshare overlay for the 4 inch display from https://github.com/swkim01/waveshare-dtoverlays (I used the overlay for linux kernel > 4.4) to /boot/overlays/
modify the /boot/config.txt by adding dtoverlay=waveshare35a,speed=14000000
someone another idea what I have to do to get this display working?