I’ve used little Raspberry Pi screen hats for various projects in the past – they are almost always a genuine pain to set up, especially if touch support needs to be calibrated, but they’re generally not more than a 30 minute job.

Except this year.

I had an old, but still on the market 3.5″ display that a student wanted to use for their project (lots of Pepper’s ghosts this year). It just would not behave with the latest Raspberry Pi OS running on a Pi 4B.

After trying the usual suspects changes: faffing about with various almost identical drivers from Waveshare and GoodTFT (I ended up deciding that our particular hardware is the knockoff one from GoodTFT, rather than the Waveshare original), tweaking various settings in /boot/config.txt and raspi-config, I stumbled upon this post.

Long story short, the old dtoverlay setting for these displays was this:

dtoverlay=tft35a:rotate=90

But that’s apparently not supported in the new Raspberry Pi OS – you need to use this:

dtoverlay=piscreen,drm

Next challenge: to get the desktop displaying. It’ll show me a terminal login (ctrl-alt-F2), but X will not start :-/