Example of writing a platform driver from scratch

This section will try to summarize as far as possible the knowledge that has been acquired so far throughout the chapter. Now, let's imagine a platform device that is memory-mapped and that the memory range through which it can be controlled starts at 0x02008000 and is 0x4000 in size. Then, let's say this platform device can interrupt the CPU upon completion of its jobs and that this interrupt line number is 31. To keep things simple, let's not require any other resource for this device (we could have imagined clocks, DMAs, regulators, and so on).

To start with, let's instantiate this platform device from the device tree. If you remember, for a node to be registered as a platform device by the platform core, the direct parent of this node must have simple-bus in its compatible string list, and this is what is implemented here:

demo {
    compatible = "simple-bus";
  ...