Linux 5.14 Mainline Should Work With The Raspberry Pi 400
The Raspberry Pi 400 for $100 USD gets you the keyboard with the Raspberry Pi built-in that offers 4GB of RAM, 1.8GHz quad-core Broadcom processor, 16GB storage, and related peripherals to have a fully-working computer and not needing any extras besides a display.
Making the Raspberry Pi 400 even more attractive is that the mainline kernel support will be here with Linux 5.14.
Queued into the SoC/SoC "for-next" branch last week was the DeviceTree addition for the Raspberry Pi 400. No kernel driver changes were needed since it's basically very close to the Raspberry Pi 4 but the updated DTS configuration is needed for the 1.8GHz clock rate, a different WiFi chip, power off handling via GPIO, and no ACT LED on the 400 model.
So thanks to the bits now queued into SoC's for-next Git branch ahead of the Linux 5.14 kernel, the Raspberry Pi 400 support should now be good to go. It's a bit unfortunate though it took so many months for this relatively straight-forward addition to be ready to go for mainline especially given the popularity of the Raspberry Pi hardware.