Getting the Raspberry Pi 4 GPU and 7-inch Touch Display 2 working was
quite challenging. Several kernel drivers are needed, beyond the
obvious VC4 and V3D, like voltage regulators and backlight controls.
Even with all the drivers enabled, I still had trouble getting
`/dev/dri/card1` (the display device, as opposed to `/dev/dri/card0`,
the 3D rendering device) to appear until I explicitly enabled the
`vc4-kms-dsi-ili9881-7inch` device tree overlay. I am not entirely sure
why this is necessary, since `display_auto_detect` supposedly should
have added this overlay automatically. I am also not sure how it would
work if I wanted to use an HDMI monitor instead of the DSI panel, but
fortunately, for this project, that's not necessary.
Dustin
6212c04f6b