so you get
- SpiDeviceDisplay
   Supports writing only, but works on top of SpiDevice, so you can use it on Linux with kernel-managed CS or userspace-managed CS.

- ExclusiveDisplay, RefCellDisplay, CriticalSectionDisplay, MutexDisplay
   Supports reading and writing, but can't go through SpiDevice. It takes an SpiBus instead. Can be used on Linux, but only with userspace-managed CS.